Link between multiple sclerosis, sun exposure and vitamin D confirmed

New data again shows that the highest prevalence of multiple sclerosis can be found in countries with the least amount of days with sun exposure, which is related to the body’s own vitamin D synthesis.

The study included data on multiple sclerosis (MS) prevalence in 104 countries, covering nearly 80% of the global population (1). The study results showed that MS prevalence increased 10% between 2008 and 2013, now affecting 2.3 million people worldwide. The further away the country was from the equator, the higher the number of inhabitants with MS was. Canada (291 per 100,000 people), Norway (160 per 100,000) and Sweden (189 per 100,000) showed some of the highest prevalence rates in the world. Looking at prevalence within a specific country – where lifestyle habits and genetics are a bit more homogenous than the entire world population – the researchers found the same kind of relationship: the states or provinces closest to the equator have the lowest prevalence of MS.

The researchers commented that these results confirm earlier data which also indicated that: the risk of vitamin D deficiency is elevated in countries with fewer days of sun exposure (due to limited endogenous vitamin D production in the skin), vitamin D deficiency seems to increase the risk of MS (2), and vitamin D supplements may help in slowing disease onset and progression (3, 4). Discrepancies in the new data indi- cate that, in some countries, the prevalence of MS seems to be influenced by other factors aside from sun exposure and/or vitamin D supply: some countries further away from the equator, for instance Russia, show low prevalence, while other countries closer to the equator, for instance Australia, show high prevalence.

MS is a condition where the body’s immune system attacks the nerves in the brain and spinal cord. It is an unpredictable condition that affects each person differently. People with MS may have some or all of the following issues: loss of balance, numbness and weakness, loss of vision, and problems speaking and think- ing. As the disease progresses, these symptoms can force many people into a wheelchair. Some studies have shown that vitamin D helps control the immune system, but the role this may play in multiple sclerosis is not fully understood.

1. Multiple Sclerosis International Federation. Atlas of MS Survey. Published online October 2013.
2. Hayes C. E. et al. Vitamin D and Multiple Sclerosis. In Vitamin D: Third Edition by Feldman, Pike, Adams. Academic Press, 2011.
3. Holmøy T. et al. Vitamin D in multiple sclerosis: implications for assessment and treatment. Expert Rev Neurother. 2012; 12(9):1101-1112.
4. Pozuelo-Moyano B. et al. A Systematic Review of Randomized, Double-Blind, Placebo-Controlled Trials Examining the Clinical Efficacy of Vitamin D in Multiple Sclerosis. Neuroepidemiology. 2012; 40(3):147-153.