MS relapses most common in the spring
A new study in Germany has reported that MS relapses are most likely to occur in the months of March and April (Hartl and colleagues. J Neurol Sci 2017;375:160-164). The risk of having a relapse was lowest in autumn.
This seasonal effect is attributed to sun exposure. Your skin uses the energy from sunlight to manufacture vitamin D, which helps to regulate the function of the immune system. Low vitamin D levels have been associated with increases in inflammatory activity in people with multiple sclerosis.
For the present study, researchers compared vitamin D levels in the blood with relapse activity in 415 people with MS. As expected, vitamin D levels were lowest during January and February, and highest in July and August. Relapse activity corresponded to seasonal changes in sun exposure with a two-month lag: relapses were most common in March/April, and least common in September/October.
A number of other groups have reported similar findings. A study in Poland found that vitamin D levels were lower in people with relapses compared to those without relapses (Brola and colleagues. Eur J Clin Nutr 2016;70:995-999). In addition, relapses were most severe in people with the lowest levels of vitamin D.
In the southern hemisphere, the lowest relapse rate was seen in February (late summer); relapses were twice as common during winter (Tremlett and colleagues. Neuroepidemiology 2008;31:271-279). The time lag between low vitamin D and higher relapse risk was 1-2 months.
Sunlight is the main source of vitamin D, but it can also be obtained from vitamin D-fortified milk products, cod liver oil and oily fish. In fact, several studies have found that people who routinely eat fatty fish have a lower risk of developing MS (Baarnhielm and colleagues. Mult Scler 2014;20:726-732). This helps to explain the low incidence of MS in people living north of the Arctic Circle, a place with little sun exposure for much of the year (Kampman and colleagues. J Neurol 2007;254:471-477). Regular consumption of fatty fish may also reduce the risk of disability progression (D’hooghe and colleagues. Eur J Neurol 2012;19:616-624). Much of this effect is due to vitamin D, but the oils may also have an impact on the beneficial bacteria in your gastrointestinal tract (much of your immune response originates in the GI tract).
Many people with MS now take vitamin D supplements every day. The usual recommended dose is 400 mg, however, your doctor may prescribe much higher doses (2,000 to 3,000 mg per day) to try to boost the levels of vitamin D in your bloodstream. This is because of studies that have shown that as vitamin D levels go up, there is a corresponding decline in the risk of having a relapse (Simpson and colleagues. Ann Neurol 2010;68:193-203).
Vitamin D supplements may be less important with the onset of summer. Several studies have found that sun exposure is beneficial – and not just because of a boost in vitamin D. (See Some (guilt-free) sun may help MS, MSology, January 5, 2017). Sun exposure is healthy in moderation – the key is not to burn the skin!
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