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samedi 30 novembre 2013

Veiled sun, vitamin D production and MS

Nichols EK, Khatib IM, Aburto NJ, Sullivan KM, Scanlon KS, Wirth JP, Serdula MK. Vitamin D status and determinants of deficiency among non-pregnant Jordanian women of reproductive age. Eur J Clin Nutr. 2012 Mar 14.

It seems that sun per se do have beneficial effects on the brain of MS patients

J Neurol Neurosurg Psychiatry 84:e2 doi:10.1136/jnnp-2013-306573.185
  • Association of British Neurologists (ABN) joint meeting with the Royal College of Physicians (RCP), London, 23–24 October 2013
  • 185


  1. Sreeram Ramagopalan
-Author Affiliations
  1. University of Oxford; Barts and the London School of Medicine and Dentistry


    Multiple Sclerosis (MS) is a complex neurological disorder most likely caused by gene–environment interactions. There is a latitudinal gradient of MS prevalence and vitamin D deficiency has been strongly implicated in MS aetiology. Iran is a country of high levels of sunshine which has previously been considered a low–risk MS region. However, Iran has recently observed an 8.3–fold rise in the incidence of MS between 1989–2006.1 Previous studies have indicated a genetic predisposition to MS in the Iranian population but genetic changes are unlikely to account for the substantial rise in MS over the last few decades. Thus, we aimed to develop a novel hypothesis to explain the identification of Iran as a high–risk MS region. We believe that the influence of decreased sunshine exposure and vitamin D levels on MS risk needs to be strongly considered in the context of Iran's history. In 1979 the Iranian Revolution took place and a country previously under great Western influences became an Islamic republic. It became a government requirement for women to wear loose–fitting clothing and the veil in public; it has previously been shown that veiled women have lower vitamin D levels compared to unveiled women. This significant cultural shift would not only potentially explain the observed increase in MS but notably, it would account for the increasing female preponderance of MS in Iran. Given that the average age of MS onset is 30 years old and that MS incidence in Iran just over 30 years following the revolution is the highest so far recorded, an association with the Iranian revolution and reduced subsequent vitamin D levels in particularly pregnant women is likely. Lifestyle changes such as urbanization and use of sunscreen may to some extent have contributed to increased vitamin D deficiency, but these are unlikely to contribute to the particularly high increase in MS observed in Iran as these changes occurred across the developed world and there is no evidence to suggest that they were particularly great in Iran. A similar high incidence of MS has been observed among Iranian immigrants in countries at high latitude such as Sweden where Iranian immigrants have a reported greater prevalence of MS compared to the general population, despite wearing a veil not being a requirement. Instead it is well–known that UVB exposure is lower in countries at high latitude and thus, a similar effect of increased MS incidence due to vitamin D deficiency may be observed among those in Iran wearing the veil and those resident in countries at high latitude, even if they are not wearing the veil. Therefore, vitamin D repletion is a critical public health issue for Iranians both within and outside Iran, and could help prevent an emerging MS epidemic in this population. More generally, this region is highly interesting for MS research and highlights that regions of exception to the latitudinal gradient of MS prevalence are an under–appreciated and very useful resource in evaluating MS aetiology.

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