Babies conceived at the end of summer have a higher risk of developing multiple sclerosis later in life than those conceived at the end of winter, a study has found.
The reason is thought to be linked to their mothers' vitamin D levels during the early stages of pregnancy. Vitamin D is created in the body by the action of the sun on the skin.
Women whose early pregnacy coincides with the summer months have higher levels of vitamin D, which may help to protect their unborn babies against multiple sclerosis. Those pregnant during winter months have lower levels of the vitamin and their babies are consequently at a higher risk.
The study, carried out in Australia, found that exposure to sunlight in the first trimester (three months) of pregnancy and the early part of the second trimester played a key role.
The chance of developing multiple sclerosis was 32% higher for children born in the early summer months at the end of a long winter than if they were born in early winter after a long summer.
In Australia, early summer falls in November and December and the researchers compared babies born at that time with those born in the early winter months of May and June.
The research, published by the British Medical Journal, reinforces previous British studies which suggested that babies born in late April or May in the UK could have an increased risk of multiple sclerosis in later life.