The risk genes for several autoimmune diseases, including multiple sclerosis, are regulated by vitamin D in particular immune cells, new research has found – but that doesn’t mean most Australians need to seek more sunlight or supplement with vitamin D, a skin cancer expert has warned.
With the help of a genetic clue from Multiple Sclerosis studies, researchers from The Westmead Institute for Medical Research’s Centre for Immunology and Allergy Research identified how immune cells are controlled by vitamin D.
They also found that this control would impact other autoimmune diseases, such as Crohn’s disease and rheumatoid arthritis.
According to Professor David Booth, who leads the Institute’s Immunogenetic Research Group, the genetic link indicates how the long-observed increase in the risk of contracting MS among those who live in areas with less sunlight might be mediated.
“It’s long been known that your risk of getting MS depended on where you grew up,” Prof Booth says.
“For example, if you grew up in North Queensland, your risk is tenfold lower than if you grew up in Tasmania. And that’s replicated around the world. The closer you are to the equator when you grow up, the less likely you are to get MS. It’s a very big difference.”
Previous research has focused on the wrong types of immune cells. But using genetic discoveries from the International MS Genetics Consortium (of which the Institute researchers were a part) Prof Booth and his team discovered that three known MS-risk genes which control vitamin D activation are turned on in myeloid cells.
Myeloid cells are a type of immune cell found in the skin and lymph nodes. Until now, nobody has looked at these cells in relation to MS and vitamin D.
With the help of a technique called ChIP-Seq, which analyses protein interactions with DNA, they found that the genes, including the risk genes, are controlled by vitamin D in the myeloid cells.
“That’s a smoking gun,” says Prof Booth. “It suggests that vitamin D controls tolerance through its gene regulation in these skin and lymph node immune cells.
“It tells you how vitamin D matters.”
But Craig Sinclair, chair of the Cancer Council Australia’s Skin Cancer Committee, says “it’s important that Australians don’t use it as an excuse to deliberately seek more sun and put themselves at risk of skin cancer”.
Most Australians get adequate vitamin D from sunlight, he says, citing the Cancer Council’s position statement on sun exposure and vitamin D, which is also approved by is approved by the Australian and New Zealand Bone and Mineral Society, the Australasian College of Dermatologists, Endocrine Society of Australia and Osteoporosis Australia.
“Essentially from the pharmacist’s point of view, the recommendation to their customers is in fact very simple,” Sinclair told the AJP.
“When the UV index is greater than 3, during periods of the year when UV levels are such that they’re likely to add to our risk of skin cancer, pharmacists need to continue to recommend sun protection – the broad suite of sunscreen, hats, protective clothing and so on.
“When we get outside that period and head into say, the winter months in the southern states when UV levels are below 3, we should not be actively promoting sun protection except for those who are outdoors for prolonged periods – people who are working on water, on roofs, on concrete, especially those who are fair-skinned.
“No one is recommending supplementation except for those people who are at high risk of vitamin D deficiency.”
People who are at high risk include dark-skinned people, people who cover up for religious or cultural reasons, the elderly, and people who are in institutions; they can benefit from supplementation possibly just during the winter months, and possibly year-round.
“But for the rest of us, leading a normal healthy lifestyle which involves outdoor activity, the risk of vitamin D deficiency is low. At this time of year, by the time you’ve gone out to the letterbox or brought in your washing, you’ll have had sufficient sun exposure to maintain sufficient vitamin D levels. You don’t have to bake in it.”
Sinclair says the best thing pharmacists can do is give customers good advice on how to protect themselves from the sun during high UV periods.
“For example, we know that people don’t use enough sunscreen, and it can only be useful when it’s an adjunct to other forms of sun protection. It’s only as good as the person applying it.”