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    Sunscreen: What science says about ingredient safety

    September 02, 2019

    Sunscreen is essential for staying protected in the Sun – but recent research suggests some of the ingredients could be improved. BBC Future analyses the evidence.

    By Jessica Brown
    23 July 2019
    Melanoma is one of the deadliest cancers. It’s also one that – while still the least common form of skin cancer – is rising in prevalence around the world. Since the early 1990s, rates of melanoma in the UK have increased among every age group. Rates of non-melanoma have increased too. In the US alone, cases of non-melanoma skin cancers have grown by around 77% over the past two decades.

    Exposure to UV radiation is the main cause of the most common forms of skin cancer. And one of the most effective ways to avoid it, of course, is sunscreen.

    “Any conversation on sunscreen must start with acknowledging that there is robust evidence that it prevents skin cancer,” says Richard Weller, honorary consultant dermatologist at the University of Edinburgh.

    This is why, although skin cancer is rising in some countries, it’s decreasing in others – particularly those that have raised the most awareness around the importance of using sunscreen. “Skin cancer rates are increasing among older generations – they’re carrying damage from decades earlier in their lives, because things have changed now,” says Adele Green, senior scientist of the cancer and population studies group at QIMR Berghofer Medical Research Institute in Australia. “Countries where rates are falling have had the biggest investments in communicating awareness, such as New Zealand, Denmark, the US and Australia.”

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    • Should everyone be taking vitamin D?
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    But some researchers have raised concerns that, despite being an undeniably important tool in our fight against skin cancer, the formulation of sunscreen may need to be improved to contain safer ingredients – and, at worst, some sunscreens could be damaging our health.

    The FDA removed 14 of the 16 chemicals found in sunscreens from its ‘generally accepted as safe and effective’ category

    Earlier this year the US Food and Drug Administration (FDA) – one of the two main global regulators of sunscreen ingredients around the world alongside the European Commission – removed 14 of the 16 chemicals found in sunscreens from its GRASE (generally accepted as safe and effective) category.

    So what is the reality?

    Double filter

    Two types of UV filters can be used for sunscreen. The most commonly used are known as organic filters, which absorb UV radiation and convert it into safer radiation. Inorganic UV filters like titanium dioxide and zinc oxide – which are broadly considered safe – reflect and scatter UV radiation away from the skin.

    It’s long been established that some organic filters are absorbed through the skin and into the bloodstream. This alone doesn’t mean sunscreen is unsafe, but there is growing focus on the potential adverse effects of the most common UV filter worldwide: oxybenzone.

    “Little is known about systemic exposure for most active ingredients” in sunscreens, the FDA stated in its report, referring to the effects of large volumes of sunscreen absorbed through the skin and into the body.

    FDA scientists authored a paper focusing on four ingredients found in sunscreen into the skin, including oxybenzone, and concluded that absorption of sunscreen into the body may be more than a theoretical concern. However, the trial was very small – involving only 24 people.

    Some lab and mice studies have found that some organic UV filters, including oxybenzone, as well as ingredients including parabens and phthalates, which can be found even in sunscreens that use inorganic UV filters, are suspected endocrine disrupters: chemicals that interfere with our hormones. But no research on humans has backed this up.

    Laura Vandenberg, associate professor at the University of Massachusetts Amherst's School of Public Health and Health Sciences, says most endocrine disrupters affect male foetuses and embryos.

    High-level exposure to phthalates has been found to disrupt development of male genitals

    High-level exposure to phthalates, in particular, has been found to disrupt development of male genitals. This could lead to problems later in life, such as reduced sperm count or increased risk of testicular cancer. However, this effect has only been found in very high doses.

    These compounds aren’t just in sunscreens, either. Phthalates also can be found in various other cosmetics, including some soaps, shampoos, nail polishes and hair sprays, and parabens are in many hair care and make-up products

    Meanwhile, Vandenberg has found through her research that oxybenzone can affect the size of mice’s mammary glands. Oxybenzone also has been detected in breast milk. That means it could also be in the breast tissue, Vandenberg says, which could affect its development, function and health.

    However, we should always be cautious when applying the findings of mice studies to humans, says David Leffell, professor of dermatology and surgery at Yale School of Medicine, who was not involved in the research.

    Critics also say research showing adverse effects of UV filters on rodents typically involved much higher levels of UV filters than human use.

    For example, in 2011, a group of researchers writing in the journal Environmental Health Perspectives put into perspective the findings of one study from 2001. In that study, researchers observed that feeding oxybenzone to young rats caused their uteruses to grow by 23%.

    The 2011 researchers calculated that to achieve the same cumulative amount of oxybenzone that was administered to the rats, the average US woman would have to apply sunscreen daily for anywhere from 34 to 277 years, depending on how many times they applied sunscreen per day.

    Male partners with higher concentrations of organic UV filter benzophenone had a 30% lower chance of conceiving

    Even so, some research has found that organic UV filters may affect humans too. In one study from 2015, researchers studied 500 couples who were trying to conceive and found that male partners with higher concentrations of benzophenone-type UV filters had a 30% lower chance of conceiving each menstrual cycle.

    “The longer time to pregnancy may be influenced by subtle changes in semen quality,” says the study’s author Germaine Louis, professor of global and community health at George Mason University in Virginia, US.

    While this is an important finding, the study does have limitations, Leffell notes, which Louis acknowledges in the paper. These limitations include reliance on only one urine measurement, and the possible variability of the concentration of UV filters measured, as their concentration lowers quickly when in the body.

    While it’s reasonable to be concerned about the clinical impact of certain benzophenones, regardless of their source, Leffell adds that the study doesn’t draw any definite conclusions.

    Vitamin D

    Aside from any one precise ingredient, there are concerns that sunscreen prevents the human body from making vitamin D, which we mostly get from Sun exposure. After all, vitamin D deficiency might be more prevalent than we think – could sunscreen use be to blame?

    It shouldn’t be a major cause, says Rachel Neale, associate professor at QIMR Berghofer. “The mechanism of sunburn is different to vitamin D production, and there is a weight of evidence suggesting that applying sunscreen doesn’t seem to influence vitamin D levels much,” says Neale.

    “We’re very good at making vitamin D. And sunscreen isn’t like being inside a room – it screens the Sun out and still lets some through.”

    A panel of 13 leading experts from around the world met in 2018 to discuss the balance of vitamin D and Sun protection and concluded that sunscreens are unlikely to affect the vitamin D status of healthy adults.

    For those concerned about getting enough vitamin D, Neale still advises wearing sunscreen every day for those living in places where there’s strong sunshine all year round, like Australia. But in places where the Sun isn’t so strong, like the UK, she says it’s easy to get vitamin D from Sun exposure because sunscreen usually is only needed when you’re outdoors for an extended period of time.

    Concerns around sunscreen blocking vitamin D production also may be overstated because so few people use sunscreen correctly, according to Weller. It’s advised we apply two mg/cm2 to our skin, around six teaspoons, which is the amount used to determine a products’ Sun protection factor (SPF). Most people apply around a quarter of that, he says.

    But could Sun exposure provide benefits other than vitamin D?

    It’s important to note that any argument emphasising the Sun’s health benefits, rather than risks, remains a controversial theory – and it doesn’t negate the warning that exposure increases the risk of skin cancer however we’re exposed to it.

    Still, one such benefit could be that UV radiation releases nitric oxide, a molecule produced in the body that dilates blood vessels and lowers blood pressure, which suggests that sunscreen may prevent these benefits, according to Weller.

    It might be that sunscreen prevents the heart benefits of Sun exposure – Richard Weller

    “A growing body of evidence suggests [nitric oxide] is important for cardiovascular health and probably reduces cardiovascular disease, which is more important than preventing skin cancer,” he says.

    Weller argues reducing the risk of cardiovascular disease is more important than reducing rates of skin cancer because, while rates of both are rising globally, heart disease kills a much larger proportion of people. Cardiovascular disease is the number one cause of death globally – 17.9 million people died from the disease in 2016, while between two and three million non-melanoma skin cancers and 132,000 melanoma skin cancers are diagnosed each year. Melanoma, the more aggressive of the two, has an estimated average survival rate of around 92%, and experts say death from non-melanoma cancers is rare.

    However, Weller acknowledges that his argument is controversial, and that the strongest body of evidence we have clearly points to sunscreen being beneficial to our health.

    Meanwhile, some argue that the confidence sunscreen gives us could be one reason why skin cancer rates are rising, particularly among older generations. Sunscreen emboldens us to spend longer in the Sun than we would otherwise, says Leffell.

    “Talking to patients, it seems people tend to not reapply sunscreen regularly when outdoors, which we need to do. The chemicals act as a sink for UV energy, and they’re not inexhaustible,” he says.

    Animal planet

    It’s not just human health that scientists are investigating. Dozens of studies have demonstrated that UV filters pose a risk to marine life. Many of these chemicals can contaminate marine mammals, sea birds, fish and corals.And while even inorganic filters, like titanium dioxide, can have an effect, one of the most toxic culprits is oxybenzone – one reason why some destinations, like Mexico’s ecological park Xcaret and Xel-Ha, have enforced a policy whereby visitors must trade in their sunscreen for one which is more biodegradable.Oxybenzone can act as endocrine disruptors and cause sex change in fish, reduced growth or egg output – Cheryl Woodley
    “Chemicals like oxybenzone can act as endocrine disruptors and cause sex change in fish, reduced growth or egg output,” says Cheryl Woodley, research scientist at the US National Oceanic and Atmospheric Administration.“Pollution in the environment from chemical sunscreens can result in a reduced resilience to climate change events, and even contribute to reproductively impaired organisms, including coral and fish, that can go locally extinct in a matter of generations by inducing sterility and reproductive failure.”In one study looking at coral communities in Hong Kong waters, researchers found higher levels of sunscreen when there is increased human activity on the coast. Some coral samples contained levels high enough to cause deformities and death in immature corals.So what should someone concerned about their health, or that of the seascape, do?Until there is definitive research on the potential effects of UV filters absorbed into our bodies, or alternatives that don’t contain ingredients associated with health risks, the consensus among experts is that we need to shield ourselves whenever we’re exposed to the Sun.The healthiest way to do so – for both ourselves and for wildlife – is with clothing, finding shade and avoiding midday Sun. But for times that isn’t possible, we should both wear sunscreen and must apply it properly.For those concerned about potential effects of UV filters being absorbed into your skin or by wildlife, a sunscreen containing inorganic filters may be the better option.That may sound simple enough. But rising skin cancer rates suggest the message has been lost.
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    The ‘silent killer’ of Africa’s albinos
    Albinos in Tanzania live in fear of witch doctors who prize their body parts, but they face a far greater threat just by spending time outdoors.

    By Ross Velton
    25 April 2017
    On stage, Sixmond Mdeka goes by the name Ras Six. He is a successful reggae singer in his homeland of Tanzania, yet despite his fame, he is haunted by another name – East Africa Yellow Man.

    Mdeka has albinism – his skin, hair and eyes lack melanin, the pigment that gives skin its colour and helps to protect it from damage by ultraviolet light from the Sun. It is a genetic disorder inherited from parents who both carry a faulty gene that prevents the skin from making melanin properly.

    Tanzania has a dark relationship with albinism. Witch doctors hunt those suffering from the condition for their body parts, which are used in potions to bring good luck and wealth. Victims can be kidnapped and then dismembered by hired killers, or even sold by unscrupulous family members, with body parts fetching up to $75,000 (£60,000). The UN estimates around 80 people with albinism in Tanzania have been murdered since 2000.

    But these brutal attacks are not the greatest threat to people with albinism in Africa. They face a slower death from a disease known as the “silent killer”. Without melanin to protect them, they have a much higher risk of getting skin cancer.

    “When you have no melanin, no protection, you’re just getting dinged, these insults from the UV radiation, you’re getting it all the time. It’s not just when you’re at the beach,” says Dr Marc Glashofer, a fellow of the American Academy of Dermatology.

    “The closer to the equator you are, the stronger the Sun, the stronger the rays, the more risk of skin cancer.”

    Albinism groups say more than 90% of people with the condition in Africa die before they reach 40-years-old. Mdeka is that age now – and the clock is ticking on his life. Last September the singer needed an operation to remove a melanoma near his left ear. "Sun is our number one enemy," he says.

    Sun is our number one enemy – Sixmond Mdeka

    But in the shadow of Africa’s highest mountain, there is an attempt to give a lifeline to people like Mdeka. Kilimanjaro Suncare, or “Kilisun”, is a sunscreen that has been specially designed for people with albinism. However, getting it to the right people – and encouraging them to use it – is far from straightforward.

    The Kilimanjaro Sunscreen Production Unit, based in Moshi on the lower slopes of Kilimanjaro, produced 15,000 jars of Kilisun last year, says Mafalda Soto Valdes, the Spanish pharmacist who developed Kilisun with Tanzania’s Regional Dermatology Training Centre.

    Wiping some of the cream on her hand, Soto Valdes explains how Kilisun is thicker than normal consumer products while also being more resistant to water and heat. It has an SPF (sun protection factor) of 30+, and the pharmacist says people with albinism need to put two milligrams per square inch of skin, twice a day.

    That’s like a “tequila shot” of sunscreen for the exposed parts of the body says Glashofer, who thinks SPF 30+ is the minimum needed to protect people with albinism in Africa.

    But using so much sunscreen so often is beyond the means of most people. "In Tanzania we’re talking about a country where 80% of the population lives with less than $1.50 a day,” says Soto Valdes. “And the cost of sunscreen is around $10, $15.”

    That’s for a bottle of normal consumer sunscreen that lasts two months. Soto Valdes says a bottle giving the kind of protection people with albinism need can be as much as $20.

    Most sunscreens in Africa are imported or donated. The continent’s largely black population has less need for protection because dark skin – which has more melanin – doesn’t burn as quickly.

    The sunscreen industry in Tanzania, however, is growing to protect its albino population, which is greater than in most other parts of the continent. Although there have been no wide-ranging studies, it’s generally thought that around one in 1,400 people have albinism in Tanzania, while in most other parts of Africa it occurs in one in every 5,000 to 15,000 people. With a population of around 50 million people, that makes albinism a major public health issue in Tanzania. In Europe and North America, by comparison, albinism is estimated to only affect between one in 17,000 and one in 20,000 of the population.

    When Kilisun came out in 2012 it was used to help 25 children. Now it’s given free to 2,800 people at clinics that take place every four months. Over half of those receiving the cream are children.

    Mdeka’s family rejected him because of his white skin – he was seen as a curse and spent his childhood living on the streets

    Mdeka can tell you that beating skin cancer starts when you’re young. His family rejected him because of his white skin – he was seen as a curse and spent his childhood living on the streets.

    ”I used to go all around the town without protective clothing,” he recalls. “I was burned by the Sun everywhere."

    Life on the streets set Mdeka on a dangerous path, which led to the melanoma on his ear following his battle with the Sun.

    Mdeka was able to get an operation for his melanoma at the Kilimanjaro Christian Medical Centre in Moshi, which is a general hospital. The only specialised hospital for cancer treatment in Tanzania is the Ocean Road Cancer Institute in the capital Dar es Salaam.

    Children with albinism, and their parents, often don't know about the importance of wearing hats, sunglasses, long sleeves and sunscreen, says Peter Ash, a Canadian with albinism whose charity Under the Same Sun helped raise funds for the Kilisun factory in Moshi.

    “We’ve actually had some parents who will take their children with albinism and put them out in the Sun to darken them up,” says Ash. “They’re trying to cause them to blend in and make them look normal. So they get all these dark-coloured lesions and they [the parents] think, ‘Oh good, they’re improving,’ when actually they’re getting skin cancer.”

    The Kilisun team is trying to address this by spending time and funds educating sunscreen users and their families. They are also trying to teach health workers and teachers about the risks of skin cancer and the best way to protect against it, says Soto Valdes, as she continues her Kilisun demonstration.

    The cream she wipes on her hand during her demonstration leaves a white smear – the robust formula, a water in oil emulsion, isn’t designed to look good and blend into the skin like most sunscreens.

    That might limit Kilisun’s appeal in some parts of the world, says Dr Andrew Birnie, a dermatologist at East Kent Hospitals in the UK, but in Africa, “the mentality is that they want to be able to see and feel that they have something on.”

    Kilisun doesn’t reach all parts of Tanzania – and finding funds to care for more people is one of Kilisun’s ongoing challenges. Mdeka uses his music to raise money to buy cream, hats and sunglasses for those who can’t afford them.

    Skin cancer has killed most of the important people in the singer’s life: his mother, father, sister – and last year, his brother. “He knew how to protect himself,” says Mdeka. “But it’s very hard to sit in the shaded places waiting while [he didn’t] have anything to eat. He was not employed.”

    Poverty trapped Mdeka’s brother in a vicious circle, as it does many people living with albinism in Africa

    Poverty trapped Mdeka’s brother in a vicious circle, as it does many people living with albinism in Africa. “They end up working outside, peddling or trading or farming,” says Ikponwosa Ero, the UN Independent Expert on albinism. “And that exposes them to skin cancer.”

    At the moment, Kilisun relies on donations from big corporations and international NGOs to continue providing cream to those who need it. The Tanzanian government also helps by providing staff.

    Kilisun’s work is part of a growing understanding around Africa about the dangers of the Sun. In 2015, the government in neighbouring Kenya said it would spend around $1.5 million (£1.2 million) to provide free Sun care products to over 3,000 people with albinism. And earlier last year it was reported that a Senegal-based company had produced 5,000 sample bottles of a new sunscreen.

    But having enough of the product and being able to distribute it to those in need are not the only challenges. Even if sunscreen were available all across Africa at an affordable price, some people with albinism might not use it.

    Twenty-two-year old Ismaili Ally from Dar es Salaam could be one of those people. At the moment he prefers to visit a traditional healer, believing oils and ointments made from plants and trees are the best way to fend off skin cancer.

    That’s where Vicky Ntetema, who runs Under the Same Sun in Tanzania, sees another vicious circle involving skin cancer. “It’s ironic that witch doctors are after them [people with albinism] and they will still go to witch doctors to find the cure for cancer,” she says.

    Ally’s healer Abdul Aziz insists there’s a big difference between his traditional remedies and witchcraft. Ally uses the products to treat the damage the Sun has already done to his skin. “The medicines are good,” he says. “When I use them, the rashes and wounds dry up within one week.”

    Soto Valdes, however, insists that prevention is always going to be better than a cure. She hopes the Tanzanian government will start buying Kilisun so the cream can reach all parts of the country. She also plans to take Kilisun to another African country – Malawi is one being considered – and bringing out a stronger cream with SPF 50+.

    Gradually, albinism’s silent killer is starting to be heard.
    Should everyone be taking vitamin D?
    Vitamin D is said to help stave off fatigue, depression and even cancer. But some experts argue that for people with healthy levels, supplements are not helpful. What’s the reality?

    By Jessica Brown
    10 October 2018
    As the days get shorter in the Northern hemisphere, concerns tend to arise about the lack of sunlight – and possible vitamin D deficiency. For many, a go-to fix is to take supplements.

    The supplement, after all, has been touted as a near-miracle. Both vitamin D2 and D3 supplements are available over-the-counter without a prescription and have been linked to improving immunity, tiredness and muscle weakness, bone pain, and depression. They’ve also been said to help stave off cancer and the consequences of ageing.

    It may be little wonder that, according to research by market analysis company Mintel, a third of adults in the UK who take vitamin supplements count vitamin D among them.

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    But the debate over whether all adults need to take vitamin D supplements is contentious.

    One study estimates that around 20% of the population in the UK has a profound vitamin D deficiency

    Few doubt the role that vitamin D plays in our bone health to regulate calcium and phosphate in the body, which is why those who have a vitamin D deficiency are particularly encouraged to address it. And that may be more people than you think: one study estimates that around 20% of the population in the UK has a profound vitamin D deficiency, for example.

    But some experts say that people with healthy levels have no need of vitamin D supplements – which would be most people. In other words, they argue that in healthy people, vitamin D is not, as some have hoped, a way to prevent disease.

    So what’s the reality?

    The basics

    Despite its name, vitamin D is not a vitamin. Instead, it is a hormone that promotes the absorption of calcium in the body. The challenge is that, aside from a few foods like oily fish, vitamin D is hard to find in the average diet. But in the presence of ‘ultraviolet B’ rays, our skin can produce its own from a common cholesterol.

    There are two main types of D. The first is vitamin D3, which is found in animals including fish and is the kind the skin makes when exposed to sunlight. The second is vitamin D2, which comes from plant-based foods including mushrooms. Studies have found that D3 is more effective, and the conclusions of a 2012 meta-analysis argue that D3 is the preferred choice for supplementation.

    Today, the UK’s Public Health England (PHE) recommends every adult takes a 10-microgram supplement in autumn and winter, when the angle of the sunlight hitting the earth prevents as many UVB rays from penetrating the atmosphere. The government body also recommends that those at risk of lower vitamin D levels, including people with darker skin, take a supplement year-round.

    Other countries follow similar guidelines. In Canada, adults are advised to get 15 micrograms of vitamin D and have two servings of vitamin-D fortified milk or soy alternatives every day, while cow's milk and margarine must be fortified with vitamin D by law. In the US, adults also are advised to get 15 micrograms, while much of the country’s milk, breakfast cereals, margarine, yogurts and orange juice is fortified, too.

    Those guidelines and fortification efforts came about largely in an attempt to fight rickets in the mid-20th Century. We know that low vitamin D levels reduce the body’s levels of calcium, which leads to a decrease in bone density and can cause rickets, particularly in babies and children.

    We also know that low vitamin D may cause muscle weakness and fatigue. One study found that low vitamin D was high among people with fatigue and that their symptoms improved after five weeks of vitamin D supplements, while a small study from Newcastle University found that low vitamin D could cause fatigue as low levels cause mitochondria, the ‘power stations’ in every cell of the body, to be less efficient. Studies of cancer patients have found similar effects. Vitamin D may also help bolster and regulate the immune system by clearing bacteria.

    Broken bones

    But vitamin D’s importance doesn’t necessarily mean people with healthy levels of vitamin D require supplements. Consider one of the most common reasons for supplementation: bone growth and maintenance.

    The current guidelines on how much vitamin D to take were informed by research involving the elderly population living in care homes, who don’t get as much exposure to the sun and are more prone to fractures and osteoporosis than the general population. But Tim Spector, professor of genetic epidemiology at King's College London, has argued that such studies are “probably flawed”.

    It’s true that the evidence isn’t clear-cut. One meta-analysis published in August 2018 concluded that increasing the levels of vitamin D in the general population is unlikely to decrease the risk of bone fractures in healthy people. And a meta-analysis of 81 studies found that vitamin D supplementation doesn’t prevent fractures or falls, or improve bone mineral density. The researchers concluded that guidelines should be updated to reflect this.

    But Sarah Leyland, osteoporosis nurse consultant at the National Osteoporosis Society, says vitamin D supplements may be useful for at-risk groups who don’t get any sunlight exposure. According to the NHS, people only need to be outside for a short period of time, with hands and forearms uncovered and without sunscreen, to get enough vitamin D between March and October.

    Healthy people won’t reduce their fracture risk by taking calcium and vitamin D supplements – Sarah Leyland

    “We know that healthy people living in the community won’t reduce their fracture risk by taking calcium and vitamin D supplements,” Leyland says. “However, people who may not be getting enough – such as those who are housebound or live in sheltered accommodation – can benefit from these supplements.”

    Still, researchers haven’t found clear evidence of that, either. One meta-analysis examining the prevention of fractures in community, nursing home and hospital inpatient populations concluded that vitamin D alone is unlikely to prevent fractures in the doses and formulations tested so far in older people. And some evidence suggests that high doses can actually result in an increased number of fractures and falls. One randomised study found that high-dose monthly vitamin D supplements increased the risk of falls among the elderly population by 20-30% compared to those on a lower dose.

    D for disease

    There is also conflicting research on the relationship between vitamin D and other diseases, even ageing.

    One main claim is that vitamin D supplements will boost the immune system. Adrian Martineau, professor of respiratory infection and immunity at The London School of Medicine and Dentistry, Queen Mary University of London, who leads a research group on the effects of vitamin D on health, has found that vitamin D plays a role in improving respiratory infections.

    When his team analysed raw data from 25 clinical trials involving 11,000 patients from 14 countries, they found a small benefit to taking daily or weekly vitamin D supplements to reduce the risk of respiratory infections, asthma attacks and bronchitis. Although the paper soon attracted robust criticism, Martineau points out that the reduction of risk, while slight, is still significant and comparable to the effects of other health measures: to prevent a single respiratory infection, you’d have to give 33 people vitamin D supplements – compared to, for example, giving a flu vaccination to 40 people to prevent a single case of flu.

    Or take ageing. One paper looking at the link between vitamin D and life expectancy found that vitamin D3 can help with protein homeostasis – the process by which proteins are regulated within cells to maintain their health. “Our observation that D3 improves protein homeostasis and slows ageing highlights the importance of maintaining appropriate vitamin D serum levels,” the researchers write.

    But other studies have been less conclusive. One meta-analysis concluded that more research is needed to clarify the effect of vitamin D on mortality. The link between cardiovascular disease and vitamin D also has yet been properly established: the link could mean that heart disease is causing low vitamin D levels, not the other way around.

    Correlation or causation?

    This is an issue with nearly all of the studies that link low D to diseases.

    If you take any group of patients with almost any disease, their vitamin D levels will be lower than in a healthy individual – Ian Reid

    Ian Reid, professor in medicine at the University of Auckland, believes that diseases cause low vitamin D levels, as being unwell often leads to spending less time outdoors exposed to sunlight, rather than vice versa. “If you take any group of patients with almost any disease, their vitamin D levels will be lower than in a healthy individual. This has led some to hypothesise it’s low vitamin D developing the disease, but there’s no evidence to prove it,” he says.

    Researchers have found that higher vitamin D levels are associated with a lower risk of colorectal cancer – it plays a role in stemming the formation of new blood vessels and stimulating better communication between cells. Vitamin D also has been found to help maintain normal levels of calcium in the colon, which slows growth of non-cancerous but high-risk cells.

    Other studies, including of the link between vitamin D and liver cancer, breast cancer and prostate cancer, suggest there is good reason to think that low vitamin D plays a part in the spread of cancer cells. But taking supplements would then, surely, help stave off cancer – and a recent meta-analysis failed to find that supplementation reduced cancer risk.

    “This is likely to be a two-way street, with cancer causing vitamin D deficiency by affecting vitamin D metabolism, dietary intake and sun exposure, and vice versa via anti-proliferative effects of vitamin D. The two hypotheses are not mutually exclusive,” says Martineau.

    D for depression

    Another oft-discussed condition is seasonal affective disorder (SAD), a mood disorder caused by the seasonal drop in exposure to sunlight. The link between light exposure and SAD is long-established. But again, a direct link to vitamin D has been difficult to prove.

    Vitamin D is associated with levels of both serotonin, important for mood regulation, and melatonin, which regulates our sleep

    Evidence suggests there may be a relationship since vitamin D is associated with levels of both serotonin, important for mood regulation, and melatonin, which regulates our sleep. Low levels of either hormone could contribute to SAD symptoms. Researchers have yet to carry out a definitive randomised control trial, however, and the exact mechanism by which vitamin D bolsters the hormones is unknown. One theory is that vitamin D receptors – which are found in many parts of the brain and concentrated in the hypothalamus, a region involved in our circadian timing – play a part in controlling the body’s hormone levels.

    Research has found that vitamin D plays a wider role in our mental health, from depression to schizophrenia, as well as in brain development, but how it plays a role also remains unclear. A meta-analysis published earlier this year found that while there is a correlation between lower vitamin D levels and depression, that didn’t necessarily mean D caused depression.

    Again, perhaps depressed people just went out less and got less sunlight.

    Sunshine serum

    If studies are inconclusive, though, perhaps that doesn’t reflect on the importance of vitamin D. Perhaps it’s the fact that most of them are based on supplements, not sunshine.

    Some scientists argue that getting vitamin D from supplements isn’t as effective as getting it straight from the sun, as the process that happens before the body makes vitamin D from sun exposure is more beneficial. More conclusive research around this is currently underway.

    Even so, most experts generally agree that even vitamin D supplements can benefit those who have very low levels. Martineau says his research found that those with low levels of vitamin D tend to see the most benefits of supplementation preventing respiratory infections, whereas the effects are a lot more modest when levels are moderately low.

    Reid says his studies have also shown benefits in those with low levels. But as most people have vitamin D levels above that threshold, they wouldn’t see benefits from supplementing.

    The trouble is that it can be difficult to predict who is at a highest risk of suffering from low vitamin D. As medical historian Roberta Bivins of the University of Warwick points out, the amount of vitamin D a person stores, and therefore requires over winter, isn’t just dependent on skin tone and the amount of time a person spend outdoors.

    It’s very individual how much sun exposure a person needs – Roberta Bivins

    “It’s very individual how much sun exposure a person needs during summer, depending on the pigment in the skin to the amount of fat in the body and how quickly your body makes new bone. It’s incredibly complicated,” she says.

    That’s why the best way to determine if you have low vitamin D is not by symptoms alone, but with a blood test arranged through your medic.

    Supplement levels

    Then there is the question of exactly what level of supplementation people need. Reid says there’s “no danger” in taking over-the-counter vitamin D of less than 25 nanomols per day.

    But with supplements offering doses as high as 62.5 micrograms available over the counter, there are concerns around the risk of excessive vitamin D levels, which can, in rare cases, cause side effects, including nausea and vomiting. In the long term, some studies suggest too much vitamin D can increase risk of cardiovascular disease, although the research isn’t conclusive.

    But others argue that even more vitamin D is needed.

    In 2012, chief medical officer Sally Davies wrote a letter to GPs urging them to recommend vitamin D supplements to all at-risk groups, writing that a “significant proportion” of people in the UK probably have inadequate levels of vitamin D. In June 2018, researchers from the University of Birmingham's Institute of Metabolism and Systems Research wrote that the death of a baby from complications of heart failure caused by severe vitamin D deficiency, and the serious health complications of two others, was just the “tip of the iceberg” in vitamin D deficiencies among those at risk

     

    How to spot misleading health news
    Follow this 10-step guide to navigating medical headlines, says Claudia Hammond, and you’ll soon weed out the flaky science and dangerous claims.

    By Claudia Hammond
    9 February 2017
    When the UK newspaper, the Independent, analysed the 20 most shared stories in the past year with cancer in the headline, more than half included claims which health authorities or doctors had discredited. Yet many millions of people had considered them interesting enough to share on social media.

    If fake news stories about politics can influence voting patterns, then could health stories about unproven treatments result in people eschewing their current medical treatment in favour of the latest recommendation in an article they see? Some fear these articles could be dangerous.

    How are people supposed to know whether something they see on Facebook or Twitter is based on good science?

    People need to be wary of what they read, but how are they supposed to know whether something they see on Facebook or Twitter is based on good science? Every day I get dozens of emails from PR companies, sometimes about very good research, sometimes about nonsense. Like other health journalists, I spend time working out how to spot which is which.

    I wondered whether the only way to be sure of the quality of what you’re reading, is to start employing the same tactics. So for the BBC’s radio series Health Check, I turned to three experienced health journalists for their tips – Sarah Boseley, the health editor of The Guardian, James Gallagher, BBC Science and Health reporter and Ivan Oransky, Watchdog Columnist at Stat News and Distinguished writer in residence at New York University. I also added a few of my own.

    1. First, look for the source of the article. Check that it’s from a newspaper, website or broadcasting organisation with a good reputation.

    2. Ask yourself whether this finding is really plausible. If it looks too good to be true, it probably is.

    3. If it’s described as “the secret that even doctors won’t tell you” then be wary. Doctors have little to gain by keeping effective treatments a secret. They want to cure people. That’s what they’re there for.

    4. The bigger the claim, the more evidence you need to see that it’s true. If this really is a massive breakthrough (and of course massive breakthroughs do happen) it will have been tested on thousands of patients, published in medical journals and covered by the biggest media around the world. If it is something so new that just one doctor is recommending it, you would do well to wait for some more evidence before following any health advice.

    5. If the article says the research has been published in a particular journal, do a quick search online to check that the journal is peer-reviewed. This means that before an article can be published, it is sent out for scrutiny by scientists working in the same field. Occasionally even peer-reviewed papers have to be retracted if the results are later discovered to be fraudulent, but the vast majority do stand. If the research has not been published in a peer-reviewed journal, be more sceptical.

    6. Has the wonder treatment been tried in humans yet? Or only in a test-tube, or in mice? If human trials haven’t taken place, the treatment could still be interesting scientifically and it could show promise, but it’s too early to say whether it will ever be a viable treatment for people.

    7. The web can save you a lot of time. Check it out on a website that reviews media coverage of news such as Health News Review, and you might find they’ve done the hard work for you.

    8. If not, search for the journalist’s name to see what they usually write about. If they regularly write about science or health they’re more likely to know the right questions to ask about a new treatment.

    9. Do an online search for the story’s details, plus the word “myth” or “hoax”. You might find it’s already been critiqued elsewhere.

    10. Finally, once you’ve established that a health story isn’t fake and has been published in a reputable journal, you might still want check the methodology of the research. NHS Behind the Headlines looks at studies in detail, discussing how they were done and whether they’ve been reported correctly in the press.

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