Tuesday, 23 April 2013

Research: Month of Birth Effect-Brazil

MS Month of birth effect pans out in Brazil as well. Will  it be due to vD deficiency in pregnancy? #MSBlog #MSResearch

EpubBecker et al. Season of birth as a risk factor for multiple sclerosis in Brazil. J Neurol Sci. 2013 Apr 15. doi:pii: S0022-510X(13)00107-X. 10.1016/j.jns.2013.03.001. 

Background: Risk factors for development of MS are still a matter of debate. Latitude gradient, vitamin D deficiency and season of birth are among the most investigated environmental factors associated with the disease. Several international studies suggest that birth in spring is a substantial risk factor for MS. 

Objectives: We investigated the season of birth as a potential risk for MS in different geographical regions of Brazil. 

Methods: We conducted a cross-sectional retrospective study with 2257 clinically definite MSers enrolled in 13 Brazilian MS clinics in the south, southeast, and northeast regions of Brazil. Demographic and clinical data relating to date of birth and clinical features of the disease were collected and analysed, and subsequently compared with birth date among the general Brazilian population. 

Results: The distribution of date of birth of MSers showed an increase in spring and a decrease in autumn, with no difference being observed in the other seasons. 

Conclusion: In conclusion, season of birth is a probable risk factor for MS in most parts of Brazil. These findings may be related to the role that vitamin D plays in MS pathogenesis.

The idea in the Northern hemisphere is that if you are born in spring you have a higher risk of developing MS. This study supports that view. However this would not be expected if the vitamin D hypothesis was correct. The closer you are to the equator the less likely there would be a month of birth effect. 


  1. Did the researchers collect VitD data, as this could be more pertinent than month of birth?

  2. Interestingly there has also been a long established season of birth effect on the risk of developing schizophrenia, which is also being linked to vitamin D deficiency amongst other factors. I knew my time at the Institute of Psychiatry would come in useful one day!

  3. The farther from the equator in the southern hemisphere should have the opposite calendar effect as the northern hemisphere i.e. MS incidence should be greater for people born in November. Does the data support this in Australia,New Zealand, South Africa and Argentina? Obviously the latitude affect and subsequent vitamin D deficiency in the southern hemisphere is not as great as in the north.

    1. Yes it does, it has the opposite effect in the Southern hemisphere.

  4. On countries on the equator the effect, if it is vitamin d, would come from when there is heavy cloud, or for cities when there is heavy smog. Looking at Brazil it does have a rainy season but it seems to vary between cities.


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