The findings, provide a biological basis as to why an individual's risk of developing the neurological condition multiple sclerosis (MS) is influenced by their month of birth, and also supports the need for further research into potential benefits of vitamin D supplementation during pregnancy, say the researchers behind the study.
Led by researchers at the University of London and the University of Oxford, UK, the study investigated the relationship between the month of birth, vitamin D status, and immune development in 100 UK-born babies.
"By showing that month of birth has a measurable impact on in utero immune system development, this study provides a potential biological explanation for the widely observed "month of birth" effect in MS," said study co-author Dr Sreeram Ramagopalan.
"Higher levels of autoreactive T-cells, which have the ability to turn on the body, could explain why babies born in May are at a higher risk of developing MS."
"The correlation with vitamin D suggests this could be the driver of this effect," he said. "There is a need for long-term studies to assess the effect of vitamin D supplementation in pregnant women and the subsequent impact on immune system development and risk of MS and other autoimmune diseases."
In the new research, samples of cord blood –extracted from a newborn baby's umbilical cord – were taken from 50 babies born in November and 50 born in May between 2009 and 2010 in London. The blood was analysed to measure levels of vitamin D and levels of autoreactive T-cells.
T-cells are white blood cells that play a crucial role in the body's immune response by identifying and destroying infectious agents, such as viruses. However some T-cells are 'autoreactive' and capable of attacking the body's own cells, triggering autoimmune diseases, and should be eliminated by the immune system during its development.
The results showed that babies born in May had significantly lower levels of vitamin D (around 20% lower than those born in November) and significantly higher levels (approximately double) of potentially harmful autoreactive T-cells, compared to the sample of November babies.