Newborn babies’ immune systems and vitamin D levels vary, depending on which month of the year they are born.

These findings come from scientists at Queen Mary, University of London and the University of Oxford and were published in the journal JAMA Neurology.

The study gives a possible biological platform as to why a person’s risk of developing the neurological condition multiple sclerosis (MS) is impacted by the month they were born in. Additionally, it identifies the need for more research into the possible advantages of vitamin D supplementation during pregnancy.

Previous studies have indicated that low doses of vitamin D are linked to harmful outcomes during pregnancy. Low levels of vitamin D during pregnancy can result in gestational diabetes and preeclampsia, as well as low birth weight in newborns.

A separate study published in the journal Neurology last year revealed that elevated levels of vitamin D during pregnancy could later prevent multiple sclerosis in the mothers.

Close to 100,000 people in the UK have MS – a neurological condition in which the body’s own immune system harms the central nervous system. This obstructs the passing of messages between the brain and other areas of the body and can result in issues with:

  • memory
  • hearing
  • muscle control
  • vision

A complicated interaction between the environment and genes is thought to lead to the development of MS.

Several population studies have indicated that the month you are born can impact your risk of developing MS. This “birth month effect” is especially apparent in England, where the risk of MS is most prevalent in people born in May and reduces in those born in November.

Similar to the way vitamin D is produced by the skin when it is exposed to sunlight – the birth month effect has been understood as evidence of a prenatal role for the vitamin in the risk of MS.

In the current study, samples of cord blood – blood taken from a newborn baby’s umbilical cord – were collected from 50 babies born in November and 50 born in May between 2009 and 2010 in London.

The blood was examined to obtain levels of vitamin D and levels of autoreactive T-cells. T-cells are the white blood cells that aid the body’s immune response by seeking out and eliminating infectious agents like viruses.

However, some T-cells are “autoreactive”, meaning they may harm the body’s own healthy cells, which can cause autoimmune diseases, and need to be expelled by the immune system during its development. This function of breaking down T-cells is done by the thymus – a specialized organ in the immune system found in the upper chest cavity.

The blood tests showed that the May babies had much lower levels of vitamin D (about 20% lower), and significantly higher levels (almost double) of these autoreactive T-cells, compared with the sample of babies from November.

Co-author Dr Sreeram Ramagopalan, a lecturer in neuroscience at Barts and The London School of Medicine and Dentistry, part of Queen Mary, concluded:

“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. 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. 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.”

Written by Kelly Fitzgerald