To go out in the sun to get the vitamin D essential for good health or to stay in the shade to avoid skin cancer? Ruth Laugesen tries to make sense of an increasingly controversial dilemma.
An oddity of human disease first piqued epidemiologist Robert Scragg's interest back in the early 1980s. No one's sure why, but winter is the killing season for cardiovascular disease. In most countries, 30-40% more people die from heart disease and strokes in winter than in summer.
For Scragg, it was the start of a decades-long interest in the role of vitamin D in protecting the body against a range of illnesses. Scragg and many other researchers had a hunch that lower vitamin D levels in the body during winter could be the reason for higher mortality from cardiovascular disease. The major source of vitamin D is the sun, with very little coming from diet.
"Each winter, vitamin D levels in the body go way down, and that's due to the sun's rays not being as strong in winter as they are in summer," says Scragg, associate professor at the School of Population Health at the University of Auckland.
The study of vitamin D in the body and its role in protecting against a wide range of chronic illnesses has become a boom area in medical research. It was already well established that low vitamin D is critical for maintaining optimum bone and muscle function, and preventing rickets and bone fragility.
But a tantalising new wave of research has found low levels of vitamin D are also associated with an astonishing array of serious conditions: internal cancers, diabetes, strokes, heart disease, multiple sclerosis, tuberculosis, osteoporosis and respiratory infections.
In New Zealand, the Health Research Council has joined the rush of research interest, putting $10 million into vitamin D research in the past five years.
The enthusiasm over the role this vitamin may play in disease protection has led to a flurry of health advice that people need to get at least some sun, particularly those with darker skins. Several months ago, the Cancer Society issued detailed advice on minimum sun exposure, putting a table on its website detailing how many minutes of sun a day are needed in summer and winter to generate adequate vitamin D levels.
But now concerns are growing that a move towards deliberate sunning, even for a few minutes a day, is too much too soon in one of the most dangerous countries in the world for melanoma. With our high UV intensity, the stakes are particularly high for getting public advice on sun exposure exactly right. Melanoma rates appear to have increased slightly in the decade to 2007, with the cancer killing about 300 people a year. (By comparison traffic accidents killed 360 in the past year.)
Some public-health experts fear that publicity over vitamin D is diluting the sun-protection message, and will lead more people to chase the sun's rays and risk damaging radiation.
Cancer epidemiologist Brian Cox, an associate professor at the University of Otago's School of Medicine, says no one should be deliberately seeking out the sun until much more evidence is in on vitamin D. It's one thing to show an association between low vitamin D and certain diseases, he says, but quite another to suggest one causes the other.
"The onus is really on showing that these claimed low levels or deficiency of vitamin D produce disease. I'm not sure that's actually shown yet. Before we get into major messages to the general public, then the evidence has to be stronger than it currently is, because there is a great potential for doing considerable harm if we get it wrong."
Scragg agrees we are at a "tipping point" - five or six years away from a clear finding on whether vitamin D is a wonder substance that protects against multiple diseases, "or fool's gold". But he says the evidence is already "compelling" for a link between low vitamin D and colorectal cancer.
Cox doesn't buy this. "There are all sorts of reasons that people would wish to believe that low vitamin D exposure is associated with colorectal cancer and that we should spend more time in the sun. I don't have any particular push in trying to obtain research funds through such claims. I've always worried that blowing up an issue will divert research funds into dead ends." He says the $10 million the Health Research Council has put into vitamin D research is "a big gamble".
Scragg responds that Cox's is only one opinion, and that he has never sought to blow up the issue by seeking publicity. He has only responded to reporters' inquiries.
In early October, after questions from the Listener, doubts at the Cancer Society over just what to advise the public led it to retract the table on its website that gave guidelines on minimum sun exposure. Skin-cancer control adviser Dr Judith Galtry says the society decided it should not be too specific about recommending exact amounts of sun exposure until more is known.
"There is no exact science on this. We are in the position of having to provide a broad-based message, and as yet there is nothing broad-based about what is known about vitamin D," says Galtry.
The table suggested that in summer, fair-skinned to olive-skinned people get "a few minutes of sun exposure to the face, arms and hands before 11am or after 4pm on most days of the week". In the winter months, they should get "approximately two to three hours of sun exposure to the face, arms and hands during the noon period across the week". For dark-skinned people, the guideline was for three to six times that amount of sun exposure, which would mean somewhere between six and 18 hours of sun a week in winter.
However, just before the Listener went to print, the Cancer Society changed its position again, saying it would "tweak" the table and reinstate it. The new table, titled "How do I take a balanced approach to sun exposure in New Zealand?" (see page 22), emphasises sun protection more strongly, and is more tentative about how much sun exposure is "sufficient" for "adequate" vitamin D in summer. In winter, the new advice is for more sun exposure: 30 minutes a day at noon. The overall effect is to re-emphasise the need for caution in summer.
Galtry says the difficulty in framing accurate advice is that the sun exposure each person needs to generate adequate vitamin D varies hugely. Whereas fair-skinned people need to keep out of the sun most of the time, dark-skinned people need more sun to manufacture vitamin D, and may at times need to seek out the sun. How much time in the sun is needed also varies by how fierce the sun is - which means taking into account latitude, time of day and season. And if that isn't enough, hidden genetic factors mean vitamin D production varies hugely from person to person.
Public interest in vitamin D has put the Cancer Society in a difficult position, says Galtry. "Vitamin D is the biggest underminer of the sun-safe message. With our very high UV levels, we find the argument for more sun very problematic until we have more evidence to support particular individual advice.
"People are using it as a justification to go out in the sun far more. A lot of people are worrying, especially epidemiologists and policy makers, that this is going to result in an increase in rates of skin cancer."
It doesn't help that the experts advising the Cancer Society are themselves poles apart in their opinions. At one end, dermatologists say no deliberate sunning is necessary at all to keep up vitamin D levels, while at the other end Scragg, the country's top researcher on vitamin D, thinks 15 minutes a day at noon in summer is desirable.
Galtry says the Cancer Society feels stuck in the crossfire. "Of all the areas the Cancer Society has been involved in, it's been a total no-win. Every way we move we get beaten up." If the society advocates any sun exposure, dermatologists call them "irresponsible", but a failure to advocate some sun exposure brings attacks from vitamin D researchers like Scragg.
The result is that the Cancer Society's current 18-page position statement on vitamin D "is as clear as mud", says Galtry. Written in 2008, it was the product of "a forum of experts arguing for a whole year. We had one expert saying you need 15 minutes minimum of sun at midday in summer, and another saying that's ridiculous, that's DNA damage."
Across the Tasman, evidence is trickling in that publicity about vitamin D means some people are being less careful about the sun. A 2009 survey of 2000 Queenslanders found reductions in sun protection by 21% of adults and 14% of children. A third of those surveyed believed fair-skinned adults and children needed to be out in the sun for at least half an hour a day in the summer sun to maintain vitamin D levels.
The authors said their research "provides evidence of reductions in sun-protection practices in a population living in a high UV environment".
Here in New Zealand, there is evidence of a change in practice for a small number of people. The Health Sponsorship Council's 2010 sun exposure survey of 1250 people asked people what they had done the previous weekend. Of those who had spent at least 15 minutes outdoors, 4% said they had spent time outdoors in the sun to improve their vitamin D levels.
Although the Cancer Society is retreating from suggestions people should deliberately expose themselves to the sun, Scragg is pushing for more sun. His position is "go out in the sun, just don't get sunburnt".
"Telling people to avoid sun exposure in the middle of the day - I don't agree with that. If you have people who are busy, there's no point in them going out at the beginning of the day or the end of the day to get sun exposure to boost their vitamin D levels, because they won't make much vitamin D at that point in time. But I think there could be a relaxing of our policy around midday sun exposure for brief periods of 10-15 minutes at time."
For its part, the Cancer Society says Scragg's advocacy of 15 minutes at midday is "irresponsible". Dermatologists, who deal with the effects of sun damage every day, are adamant that we can get all the vitamin D we need through incidental exposure.
Dr Louise Reiche represented the New Zealand Dermatological Society on the Cancer Society working group on vitamin D. Reiche, who is fair-skinned and wears sunblock every day of the year, says she gets all the vitamin D she needs from the sun in the course of outdoor activity while sun-protected, and through a diet rich in fish and omega-3 oils. She knows, because she has had her vitamin D blood levels checked.
Is there any time of the year that she would deliberately expose herself to the sun without sun protection? "No, not typically. In August and September, when the UV is starting to climb, I could allow myself five minutes if I'm hanging out the washing and I knew it wasn't going to be any longer. I know that would enable me to not get any signs of redness.
"I know even when I'm putting the sunscreen on that the sun does get through, and I will manufacture some vitamin D through that. The optimal level to generate the best vitamin D is actually a tiny amount of sunshine, so that's even less than you would be able to see - any minimal redness on the skin. It's way less than any sign of sunburn."
"We see day in and day out people with skin cancers. Sometimes with the scars they have from their skin cancers they may not be able to move their arms and limbs freely, they may lose part of their ears."
And she says research is showing that people exercising outdoors can achieve a higher vitamin D level than somebody who is sunbathing, because of the way the body processes vitamin D. The best way to optimise vitamin D while also protecting the skin from damage is "encouraging New Zealanders to be physically active outdoors, but at the same time covering up".
And she says sunning yourself in winter, when vitamin D levels in the body drop, is pointless. "We get very low levels of UV in our winter, so even if you were brave enough to stand naked in the midday sun in the winter, you would not be able to generate vitamin D from the sun at all." (However, Richard McKenzie, principal scientist in atmospheric processes with Niwa, says this is in contention.)
A leading international researcher on vitamin D, Professor Rebecca Mason of Sydney University, says there is no doubt sun protection or sun avoidance is required if you are out for more than a few minutes in summer. "As it turns out, vitamin D is best made by short frequent exposures."
Her advice on the right exposure for vitamin D is this: in summer, at morning or afternoon tea time, six to eight minutes exposure of the face, arms and hands. You're trying to get about a third of the UV exposure that would produce faint redness.
If the experts are scrapping over vitamin D, it's partly because the holes in the knowledge are massive. One gap is in the relationship between sun exposure and vitamin D levels in the body. (Scragg received a $1.7 million grant for research on this in 2007 but has yet to produce his findings.) Second, more needs to be known about the relationship between low vitamin D levels and a range of diseases. Third, does protection from disease have to be delivered via the sun, or can vitamin D supplements do the trick? And fourth, is vitamin D the magic ingredient affecting disease rates, or might there be something else at work? For example, those with good vitamin D levels might be doing other things right, such as getting lots of exercise. Their vitamin D levels might be high because of exercise outdoors.
There's even a scrap over what rates of vitamin D count as deficient. "There's a big global bunfight about this," says Mason.
The Ministry of Health says a level of 17.5 nanomoles per litre of blood counts as deficient, and on that basis 3% of the New Zealand population are deficient. But many local researchers are pushing for much higher levels to count as deficient. Mason says there is solid evidence that 50-60nmol/L is optimal for maintaining bone and muscle function. But it is at 70-80nmol/L that some of the exciting protective associations have been found with cardiovascular disease, cancer and diabetes. At that level, the great majority of the New Zealand population is deficient. In 1997, 84% of the adult population had less than 80nmol/L. The mean adult level was 50nmol/L, with 42 for Maori and 37 for Pasifika people.
If 80nmol/L does turn out to be a benchmark for good health, public health experts will either be pushing for New Zealanders to get a lot more sun, or to be mass-medicated, either through supplements or food fortification.
Could vitamin D be a magical ingredient that influences health status across a huge range of illnesses? Mason laughs. "I have a problem with snake-oil salesmen. There is a possibility that it does contribute in a small way to a number of things."
Scragg sympathises with the Cancer Society's dilemma over what to advise the public on vitamin D. But he says the Ministry of Health should be driving policy.
"The Cancer Society does have a conflict of interest when it comes to setting health policy. On the one hand, it's telling people to stay out of the sun and also to use its sunscreen products, and on the other hand it's making money out of these sunscreen products."
For its part, Galtry says the Cancer Society no longer wants to solely carry the load in vitamin D policy making. In fact, the Ministry of Health is gearing up its interest in vitamin D, with a discussion paper on it due out in December.
"The ministry is reviewing the evidence, including the health effects of vitamin D deficiency and insufficiency, the current situation in New Zealand, the identification of factors affecting vitamin D status, and the policy options/approaches," says a statement from public health medicine specialist at the ministry Dr Harriette Carr.
Asked what policy options were under consideration, Carr said: "Policy options must consider the ways that vitamin D levels can be increased. Vitamin D levels can be increased through sun exposure, dietary vitamin D intake, vitamin D supplementation and/or fortification."
Meanwhile, there are also signs of activity at the body responsible for food fortification, the New Zealand Food Safety Association. It's running an experts' roundtable on vitamin D this month "to get a clear perspective from scientific and technical experts what actions, if any, NZFSA should be considering in this area".
In the US, vitamin D fortification of milk and many other foods is mandatory, as it is for butter and margarine in the UK. In Australia, fortification of edible oil spreads is mandatory; these are now a major dietary source of vitamin D. But any attempts to fortify food here will come up against the lobbying power of the New Zealand Food and Grocery Council, which vigorously fought against mandatory folic acid in bread, and had its introduction delayed until 2012.
The quest to find whether vitamin D has a major role in protecting against illness has now moved into a more decisive phase, with a series of clinical trials to compare the health of those who take vitamin D supplements with those who don't.
Scragg is leading a $5 million project, involving more than 4000 Aucklanders over 50. Half will take monthly vitamin D supplements, and half will take a placebo for four years, with researchers tracking how many in each group develop cardiovascular disease or respiratory problems. Cox describes the research as another "big gamble and I don't think it's likely to come to anything".
Scragg replies: "One of the main reasons many researchers support this research is that vitamin D is incredibly cheap. The cost of a year's supply for one person could be as low as $1. That's why we need to do clinical trials to find out whether it is beneficial or not. The implications for public health are immense if it is."
And until the research becomes a lot clearer, there's one thing the experts do agree on about New Zealand's sun: be careful out there.