This led to the suggestion that the mother’s vitamin D status during pregnancy may affect a person’s risk of developing MS later in life.
In humans, the majority of vitamin D required by the body is synthesised in the skin in response to ultra-violet light. Only a small proportion of vitamin D is obtained from the diet, in foods such as dairy and oily fish. Hence vitamin D levels in the blood are generally much lower towards the end of winter.
Despite the data suggesting that the month of birth affects MS risk, until now no study has directly assessed the relationship between vitamin D levels at birth and MS risk.
Blood spots have been taken from new born babies in many countries since the 1970s for the identification of certain genetic disorders such as phenylketonuria (PKU).
Danish researchers have now taken advantage of this resource to examine the vitamin D levels in the blood spots taken at birth from 459 people with MS and 663 control individuals without MS.
The results, published in Annals of Neurology earlier this month, showed that there was no difference in vitamin D levels at birth in the people who went on to develop MS compared to those who did not.
There was a clear season of birth effect in levels of vitamin D in the blood spots, but this did not correlate with risk of MS.
Questionnaires completed by the people with MS and control individuals also collected data on potential factors from early life or adulthood that might have affected the results including whether they were breastfed, month of birth, latitude of birth, adult vitamin D intake from dairy and fish, smoking, body mass index and socioeconomic status.
When all of these factors were taken into account, the results did not change – there was still no association between blood spot vitamin D levels and risk of MS.
A large number of studies have strongly linked low vitamin D levels and low sun exposure with a higher risk of MS, but there has been some disagreement among scientists as to what point in a person’s life these factors have the most impact on MS risk.
Several studies, including the pivotal Australian Ausimmune study which was supported by MS Research Australia, have shown that vitamin D deficiency is more commonly present in people presenting with their first MS attack compared to the healthy population. This new Danish study adds weight to the argument that it is vitamin D and/or sun exposure levels in later life that more strongly influence the risk of MS.
MS Research Australia is currently funding and co-ordinating the PrevANZ clinical trial which is testing whether oral vitamin D supplementation can prevent or delay a diagnosis of MS in people who have experienced a first demyelinating event. The results of this trial are expected in 2017 and will provide vital information on the efficacy and optimal dose of D.
People with MS concerned about their vitamin D levels should consult their GP or neurologist for further information and advice.