CHILDREN conceived during the winter months are more likely to suffer from learning disabilities, Scottish research has revealed.
It is thought lower levels of sunlight leave pregnant mothers short of vitamin D and this affects the baby's developing brain.
Autism, dyslexia and intellectual difficulties were all higher among children conceived during the darkest months of the year in Scotland with problems peaking among those conceived in February.
The researchers, who looked at birth and educational records for more than 800,000 Scottish children, are urging women to take vitamin D supplements as soon as they start trying to start a family.
Professor Jill Pell, director of the Institute of Health and Wellbeing at Glasgow University which led the study, said: "Vitamin D is very important for brain development in the child and the first three months (after conception) are the critical period when the brain develops. We know from some animal experiments that if you deprive animals of vitamin D there are brain development problems with their offspring and if you give them vitamin D the brain development resolves."
The study, published in the American Journal of Epidemiology, found 8.9 per cent of children who had been conceived between January and March had learning disabilities, compared to 7.6 per cent conceived between July and September.
Children who started life in October, November and December were also more vulnerable to learning issues than those conceived during summer months.
The time of conception for 801,592 children who attended Scottish schools between 2006 and 2011 were calculated for the study, based on their date of birth. School census information was consulted to identify those with a record of special educational needs.
Although the researchers, who worked in collaboration with the Scottish Government and the NHS and Cambridge University, were not able to measure vitamin D levels as part of the study they have suggested it is “the most plausible explanation for the trend”.
Professor Pell 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.”
Other health problems linked to learning difficulties such as visual or hearing problems, or physical illness, did not vary according to date of conception.
The children in the study were born prior to 2012 guidelines suggesting that all pregnant women should take vitamin D supplements in order to prevent other conditions such as rickets.
Last month an extensive scientific review sparked new official advice for everyone to take vitamin D supplements during the autumn and winter.
Professor Pell said: “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.”
Across the UK there is insufficient sunlight from January to March for pregnant mothers to produce vitamin D.
Professor Pell said: "Certainly as you go further north you have less sunlight and vitamin D but in reality, the whole of the UK just does not have enough sunlight. Particularly if you are dark skinned, it is very difficult to produce vitamin D."
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 greater risk of catching flu between January and March could also be a factor in their findings.
Earlier this year the Scottish Government announced plans to give all pregnant women free vitamins to help with their babies’ development. Some women are already entitled to supplements, but this is due to be extended to all by next Spring.
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