January 5, 2017 | News | MS Research

Some (guilt-free) sun may help MS

The official line from health officials for the past few decades has been to avoid sun exposure because of the risk of melanoma skin cancer. However, some researchers are now saying that too little time in the sun has become a major public health problem, especially in northern countries such as Canada (Hoel and colleagues. Dermatoendocrinol 2016;8:e1248325; Grant and colleagues. Dermato-Endocrinology 2016;8:e1248324). The health problems caused by too little sun, the authors say, far outweigh the risk of skin cancers.

It hasn’t been determined if low sun exposure has contributed to the increasing frequency of multiple sclerosis, but researchers have speculated about the link between sunlight and MS for decades. The prevalence figures for show a “latitude effect” – MS is increasingly common as you move farther away from the equator.

The most obvious link between sunlight and MS is vitamin D – a hormone produced by our bodies when our skin is exposed to the sun. If there is too little sun exposure, we can develop a vitamin D deficiency. For example, in the Canadian Health Measures survey, 6% of the population were deficient in vitamin D, and another 25% had low vitamin D levels. During the winter months, over one-half of the Canadian population has low vitamin D levels.

In the U.S., about 40% of people have low vitamin D levels (Looker et al. NCHS Data Brief, No. 59, March 2011). So an estimated 150 million people in North America alone have inadequate levels of vitamin D.

One of the more severe health consequences of vitamin D deficiency is rickets, which has largely been eliminated by adding vitamin D supplements to foods, such as milk and bread. But even vitamin D insufficiency, a less severe form, can have an impact on how well the immune system functions. In MS, low vitamin D levels have been shown to increase the risk of developing MS in people with early neurological symptoms (Martinelli and colleagues. Mult Scler 2014;20:147-155). People with MS have more inflammatory activity in the brain, more relapses, faster progression, and more disability over the longer term (Ascherio and colleagues. JAMA Neurol 2014;71:306-314; Thouvenot and colleagues. Eur J Neurol 2015;22:564-569).

That said, clinical trials to date have posted somewhat disappointing results when people with MS were given vitamin D supplements to boost their blood levels (Kampman and colleagues. Mult Scler 2012;18:1144-1151; Stein and colleagues. Neurology 2011;77:1611-1618). The best findings have been when people take vitamin D along with an interferon (Rebif, Avonex, Betaseron); MRIs showed that the combination reduced brain inflammation (Loken-Amsrud and colleagues. Neurology 2012;79:267-273; Soilu-Hanninen and colleagues. J Neurol Neurosurg Psychiatry 2012;83:565-571; Smolders and colleagues. ECTRIMS 2016; abstract 166).

More recently, researchers in Boston compared vitamin D taken with different MS medications (Rotstein and colleagues. Neurol Neuroimmunol Neuroinflamm 2015;2: e167). They found that people taking an interferon had fewer relapses and fewer new lesions with vitamin D compared to an interferon alone. There was also a benefit when people took vitamin D with Gilenya: they had fewer relapses and developed new lesions more slowly. Interestingly, there was no benefit to combining vitamin D with Copaxone, for reasons that aren’t immediately apparent. Other MS medications weren’t tested in this study.

Vitamin D supplements may only be part of the answer. It is likely that the benefits of sun exposure occur, in part, through mechanisms that don’t involve vitamin D. This was seen in an Australian study, which showed that the benefits of sun exposure were independent of those of vitamin D in people with MS (Lucas et al. Neurology 2011;76:540-548).

The key to healthy sun exposure is to avoid a sunburn, which damages the skin and increases the risk of skin cancer. In fact, one study found that people with greater non-burning sun exposure had a lower risk of melanoma (Gandini and colleagues. Eur J Cancer 2005;41:45-60).

The amount of time you can safely expose yourself will depend on many factors, such as the amount of pigment in your skin (which acts as a natural sunblock), the intensity of the sunlight (more intense as you approach the equator), time of year, time of day, and so on. But even fair-skinned people can benefit if they don’t overdo it.

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