Multiple Sclerosis: risk factors

The causes of multiple sclerosis (MS) are not fully understood. The disease is more common in northern-most and southern-most latitudes (Kurtzke (1997)) and there is evidence that it is more common in the northern than the southern parts of the UK (Kurtzke (1997)Forbes and Swingler (1999)). There is some evidence of temporal and geographical clusters (Kurtzke (1997)Donnan et al (2005)). These findings have been interpreted as suggesting an environmental cause, such as an infectious agent, and some studies have found an association with infection with the Epstein-Barr virus (Lucas (2011)).  Smoking is associated with a substantially increased risk of MS. As well as being more common further away from the equator, the disease is also more common among children born in winter months (Willer et al (2005)). These observations have generated interest in the possible role of vitamin D. A number of observational studies - see reviews by Munger (2011) and Ascherio et al (2010) - have found an association between low levels of vitamin D and an increased risk of multiple sclerosis, but there is a lack of evidence about whether increasing vitamin D intake could prevent or treat MS.