Shining Light on Vitamin D

Australian Doctor, 30 March 2007

Some experts now believe that one in four Australians may have sub-optimal levels of vitamin D. Australian studies also suggest vitamin D deficiency mat effect 80% of dark-skinned women during pregnancy and up to 76% of elderly people in institutions

But although there is no dispute the problem exists, the question of what to do about it remains vexed, not least because studies suggest 80 – 100% of vitamin D comes not from diet but from UV exposure.

Professor Rebecca Mason, professor of physiology at the Bosch Institute at the University of Sydney, says discussing the possible benefits of sun light can be tricky for health professionals, given concerns about the dangers of sun exposure.

“We don’t want the majority of people to increase their sun exposure or we will undo 20 years of really good work by the Cancer Council,” she says.

Professor Mason who is also a board member of Osteoporosis Australia is one of the experts who contributed to a multidisciplinary position statement on the risks and benefits of sun exposure first released in 2005, with a revised version expected soon.

“Constant deliberate sun exposure without any form of sun protection when the UV index is above three is not recommended, even for those diagnosed with vitamin |D deficiency,” the statement says. “The small amount of sunlight received on the face, hands, arms or legs during normal outdoor daily activities is usually all that is required to absorb appropriate levels of ultraviolet radiation.

“Where there is vitamin D deficiency, oral vitamin D supplementation, rather than relying on sun exposure, may be necessary.”

Professor Mason says the recommendations have been formulated on the best advice available, but many questions remain. For a start the is no certainty about the optimal level of circulating vitamin D. Australia currently advices 50nmol/L but the US is suggesting closer to 80nmol/L, Professor Mason says.

And there isn’t as good data as we would like on how much sunlight we need to maintain adequate vitamin D levels” she says. “There have been precious few studies that we have had to extrapolate from to work out what we are recommending.”

Recommendations also need to vary depending on a person’s skin tone, the season, time of the day and the latitude at which they live.

The obvious alternative to sunlight is adding vitamin D supplements or fortified foods to the diet, but even here Professor Mason says there are problems. The vitamin D supplements available in Australia are of a relatively low dose and need to be taken regularly, which creates problems with compliance. And although very high doses are needed before risking toxicity, the long term safety is unknown, she says.

“It’s probably not a good idea to mass medicate and the other argument is that we can not exclude the possibility there are beneficial effects of sunlight that are not made up for by giving vitamin D; we just don’t know.”

Adding to this complex picture is emerging evidence suggesting the benefits of vitamin D extend beyond preventing rickets, osteomalacia and osteoporosis.

Professor Mason and colleagues are researching suggestions that vitamin D produced in the skin may actually protect against DNA damage from UV radiation.

Professor Bruce Armstrong, professor of public health at the University of Sydney and director of research at the Sydney Cancer Centre, says there is some evidence to suggest vitamin D has a protective effect against cancer, auto-immune disorders such as multiple sclerosis and type 1 diabetes, and possibly hypertension.

The first clear evidence demonstrating the antineoplastic effects of vitamin D emerged in the early 1980’s he says. His own research shows increased sun exposure has a protective effect against non-Hodgkin’s lymphoma, and that patients diagnosed with melanoma have a better outcome if they are diagnosed during summer rather than winter. While many questions remain about the effects of vitamin D and whether sunlight itself gives additional health benefits, Professor Armstrong says one thing is clear – the entire issue is much more complex then previously thought.

“I think our biggest problem at the moment is seriously being sure we know the balance of risks and benefits with respect to sun exposure. How much sun exposure you can get and gain net benefit rather than net harm,” he says.

“We need a much better process for working out how you reconcile the balance between the beneficial effects of vitamin D and the harmful effects of sun exposure. Even when we have done that, we still face the problem of how can we effectively communicate to people so we can feel that they are safe.”

The Australasian College of Dermatologists, which contributed to the sunlight position statement, last year issued two press releases criticizing media coverage of the sunlight debate for encouraging increased UV exposure among the general population. Australians have the highest rate of skin cancer in the world, the college said.

Honorary secretary Dr Stephen Shumack suggests the key message in the revised position statement will remain the same; that a few minutes sun exposure outside of the midday period may not be harmful, unless an individual has skin cancer risk factors. Although he acknowledges the suggestion sunlight itself may provide health benefits, Dr Shumack says supplementation appears to be the safest remedy for vitamin D deficiency.

“There is not hard evidence to suggest that vitamin D supplementation is any less effective than sun exposure,” he says.

The Cancer Council has also been involved with both the original and revised position statements and its CEO Professor Ian Olver, says the organization wants to ensure its Sun

Smart message remains sound in the face of the emerging vitamin D evidence. The council doesn’t want the Slip Slop Slap message to be interpreted as meaning any sun exposure is bad.

“But the first thing to say is that most Australians will get enough sun exposure for vitamin D production just in their normal activities,” he says.