A new study carried out by scientists from the Universities of London and Oxford may provide clues as to why the risk of developing multiple sclerosis (MS) is influenced by month of birth - it seems that vitamin D levels and immune system development vary according to month of birth in newborn babies.

MS is a disabling neurological condition which happens when the body's own immune system attacks and damages the central nervous system. This interferes with the transmission of electrical messages between the brain and the rest of the body - leading to problems with vision, muscle control, hearing and memory.

Previous population studies already indicate that month of birth can influence risk of getting MS. This effect is particularly evident in England, where MS risk peaks in individuals born in May and drops in those born in November. As vitamin D is formed by the skin when it is exposed to sunlight, this effect may support a prenatal role for vitamin D in MS risk.

In this new study, blood was extracted from the umbilical cord of 50 newborn babies and analyzed to measure levels of vitamin D and autoreactive T-cells. Autoreactive T-cells are specialized immune cells whose role is to identify and destroy infectious agents such as viruses.

However, for some reason, some of these T-cells start attacking the body's own cells, triggering autoimmune diseases such as MS. Normally such self-harming T-cells should be eliminated by the immune system during its development by the thymus, a specialized organ in the immune system.

Study results showed that babies born in May had significantly lower vitamin D levels (around 20% lower than those born in November), along with nearly double the number of autoreactive T-cells compared to November babies.

In other words, lower levels of vitamin D in May babies are associated with twice the levels of autoreactive T-cells, which naturally increase the risk of damage to the central nervous system.

In the future, long-term studies are needed to understand whether vitamin D supplementation in pregnant women can impact immune system development and lower risk of MS and other autoimmune diseases.