Low vitamin D levels in pregnant women could be linked to some learning disabilities in children, research suggests.
Glasgow University scientists found that more children conceived between January and March had conditions such as autism and dyslexia than those conceived during summer months, after examining more than 800,000 Scottish children.
The first three months of pregnancy are important for brain development, yet there is not enough sunlight in the UK between January and March for pregnant mothers to produce vitamin D.
Previous experiments have shown that a lack of vitamin D can impair brain development.
Lead author Professor Jill Pell said lack of vitamin D is “the most plausible explanation for the trend” and urged women to take supplements when they were trying to get pregnant.
She said: “The results of this study show that if we could get rid of the seasonal variation, we could prevent 11 per cent of cases of learning disabilities.
“It is important that pregnant women follow the advice to take vitamin D supplements and also that they start supplements as early in pregnancy as possible; ideally when they are trying to get pregnant.”
The children in this study were born before the 2012 guidelines suggesting that all pregnant women should take vitamin D supplements.
Professor Gordon Smith, head of the Department of Obstetrics and Gynaecology at Cambridge University, said: “If vitamin D levels do indeed explain the seasonal fluctuations observed in this study, we would hope that widespread compliance with the advice would lead to loss of this variation, and would have a downward effect on overall rates of special educational needs.
“Although the current study did not directly measure vitamin D, it remains perhaps the most plausible explanation for the trend.
“Hence, these findings underline the importance of health professionals recommending vitamin D, and the importance of women complying with the treatment to optimise their chances of a healthy child.”
The authors noted that an increased risk of flu infections early in pregnancy could also be a factor in the statistical variation, as January to March are the peak months for flu.