24 August 2016 - PubMed - Low vitamin D during pregnancy linked with learning disabilities

Writing in the American Journal of Epidemiology, the research team found that 8.9% of children conceived between January and March had learning disabilities. This compared to 7.6% of children conceived between July and September.

The team from the Universities of Glasgow and Cambridge point toward the lack of sunlight in the UK during the first three months of the year as the most plausible explanation.

Sunlight is a primary source of vitamin D and during these months sunlight doesn't contain enough UVB radiation for the skin to make vitamin D.

Here vitamin D is primarily obtained from food sources including fortified foods and supplements. Pregnant and breastfeeding women in particular are advised to take a daily 10 μg vitamin D supplement.

Seasonal variations

Lead by Professor Jill Pell, director at the University of Glasgow's Institute of Health and Wellbeing, the team looked at 801,592 children attending Scottish schools between 2006 and 2011.

Children’s birth months were recorded and correlated to the educational needs of the children.

The number of children that received extra assistance in school was at its highest among children conceived in the first quarter of January to March and lowest in the third quarter of July to September at 8.9% and 7.6%, respectively.

Seasonal variations also remained a significant factor to other neurological conditions such as autistic spectrum disorder, intellectual disabilities and learning difficulties such as dyslexia.

However, the team found the month of birth had no bearing on sensory or motor/physical impairments and mental, physical or communication problems.  

In total, seasonal variations accounted for 11.4% of all cases.

“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,” said Professor Gordon Smith, head of the Department of Obstetrics and Gynaecology at the Cambridge University and co-author of the study.

“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."