Low vitamin D levels may lead to learning disabilities

03 October 2016
Pregnant woman in the sun

A new study has found that learning disabilities are more common in children conceived in the winter months when there is insufficient sunlight to produce vitamin D.

The University of Glasgow  study, recently published in the American Journal of Epidemiology,  found that nearly 9% of children conceived in the Northern Hemisphere winter (between January and March) had learning disabilities.

In contrast only 7.6% of those conceived between July and September (the Northern Hemisphere Summer/Spring) had learning disabilities.

The overall difference was due to autism, intellectual difficulties and learning difficulties such as dyslexia. There were no seasonal patterns for other causes of learning difficulties, such as visual or hearing problems, or physical illness.

The researchers did not measure Vitamin D levels in this particular study, but suggest that this is “the most plausible explanation for the trend” as there is insufficient sunlight in January to March for pregnant mothers in the UK to produce vitamin D and the first three months of pregnancy are known to be an important time for brain development.

In New Zealand, Vitamin D deficiency has also been raised as an issue as there have been a rising number of cases of rickets in young children due to a deficiency in the crucial vitamin.

Professor Jill Pell, Director of the Institute of Health and Wellbeing, says: “The results of this study show that if we could get rid of the seasonal variation, we could prevent 11% of cases of learning disabilities.”

The research linked health and education data collected routinely from across Scotland in order to study more than 800,000 children who attended Scottish schools between 2006 and 2011.

Professor Gordon Smith, Head, Department of Obstetrics and Gynaecology, Cambridge University, says: "Although the current study did not directly measure vitamin D, it remains the most plausible explanation for the trend. Hence, these findings underline the importance of vitamin D."

The New Zealand Ministry of Health says women need adequate levels of Vitamin D during pregnancy to ensure optimal development for baby.  They advise:

  • Time in the sun
        o Between May and August: around the middle of the day
        o Between September and April: before 10am and after 4pm

  • Eating foods which supply Vitamin D such as oily fish, eggs, milk and yoghurt

  • The following people may be at greater risk of having low vitamin D levels and should consult a doctor if they are concerned:
        o Those who live in the south of the South Island
        o Those with darker skin
        o Those who spend a lot of time inside
        o Those with liver or kidney disease
        o Those who take certain medications, such as anticoagulants.

Find out more about the UK study here.