Antenatal Solar Radiation Associated with Learning Disabilities in Offspring

by | Jun 16, 2020 | 2019, Infant and Children's Health

Written by Joyce Smith, BS. This study suggests that low ultraviolet (UV) B exposure in winter months may be contributing to the seasonal patterning of learning disabilities seen in children.

infants and childrenLearning disabilities not only profoundly impact the affected child but also have enormous consequences for the families and for society as a whole. The estimated lifetime cost of raising an affected child has been estimated to be in excess of 51 billion dollars 1. During the antenatal period, the fetus undergoes rapid development and growth, making it susceptible to environmental exposures and their potential long-term consequences. One study suggested that low exposure to UV radiation may be responsible for the higher incidence of autism in high latitude countries, urban areas, and dark-skinned people 2. A previous study by Hastie and colleagues demonstrated that 11.4% of all learning disabilities were associated with the month of conception 2.  Identifying and addressing modifiable risk factors could potentially reduce the financial burden of health care to parents, families and communities 3. Studies have shown that people living in high latitude countries are very often vitamin D deficient because of lack of sufficient sunlight 4. Pregnant mothers must have adequate levels of serum vitamin D for normal fetal brain development 3 and exposure to UVB radiation is necessary for vitamin D production. Therefore, the Hastie team hypothesized 5 that the seasonal variation in maternal vitamin D levels over the critical period of brain development may account for the seasonal patterning of learning disabilities seen in  children.

The team compared the 2007–2016 Scottish School Pupil Censuses to Scottish maternity records and to the number of hours of sunshine hours as determined by weather stations and the amount of antenatal UVA and UVB radiation exposure as determined by satellites. They used logistic regression analyses to explore the associations between sunlight, then UVB exposure, and learning disabilities seen in children. After adjusting for the potential confounding effects of month of conception and sex, they found that of the 422,512 eligible, single birth school children born at term in Scotland, 79,616 (18.8%) had a learning disability: 49,770 (23.1%) were boys and 29,846 (14.4%) were girls. There was a dose-related statistically significant inverse association between the risk of learning disabilities and the total antenatal sunshine hours (P<0.001) and between risk of learning disabilities and UVB exposure over the entire length of pregnancy (P<0.001). The UVB exposure was independent of UVA exposure. The percentage of children with learning disabilities varied by month of conception, ranging from 16.5% among children conceived in July, to 21.0% among those conceived in February, March and April.

Boys have a different seasonal pattern to conception from girls; with male conceptions peaking in autumn and female conceptions in spring 6. Boys are also more prone to some types of learning disability, such as autism and attention deficit hyperactivity disorder 7,8. Therefore, adjustment for the child’s sex was a strength of the study. However, calculations of UV exposure were accurate only if women lived in Scotland for the full duration of their pregnancies. There was no available data to account for changes in UV exposure due to holidays and trips abroad or for individual differences in UV exposure due to varying times spent outdoors, use of sunblock, or choice of clothing.

Low maternal exposure to UVB radiation may play a role in the seasonal patterning of learning disabilities. Further studies are required to validate the present findings and to determine a potential role for Vitamin D supplementation in the prevention of learning disabilities.

Source: Hastie, Claire E., Daniel F. Mackay, Tom L. Clemens, Mark PC Cherrie, Albert King, Chris Dibben, and Jill P. Pell. “Antenatal exposure to solar radiation and learning disabilities: Population cohort study of 422,512 children.” Scientific reports 9, no. 1 (2019): 1-6.

© Open Access licensed under a Creative Commons Attribution 4.0 International License http://creativecommons.org/licenses/by/4.0/.

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Posted June 16, 2020.

Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from  the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.

References:

  1. Honeycutt AA, Grosse SD, Dunlap LJ, et al. Economic costs of mental retardation, cerebral palsy, hearing loss, and vision impairment. Using survey data to study disability: Results from the National Health Interview Survey on Disability. 2003;3:207-228.
  2. Cannell JJ. Autism and vitamin D. Medical hypotheses. 2008;70(4):750-759.
  3. Mackay DF, Smith GC, Cooper SA, et al. Month of Conception and Learning Disabilities: A Record-Linkage Study of 801,592 Children. Am J Epidemiol. 2016;184(7):485-493.
  4. Holick MF. The vitamin D deficiency pandemic and consequences for nonskeletal health: mechanisms of action. Mol Aspects Med. 2008;29(6):361-368.
  5. Hastie CE, Mackay DF, Clemens TL, et al. Antenatal exposure to solar radiation and learning disabilities: Population cohort study of 422,512 children. Sci Rep. 2019;9(1):9356.
  6. Cagnacci A, Renzi A, Arangino S, Alessandrini C, Volpe A. The male disadvantage and the seasonal rhythm of sex ratio at the time of conception. Human reproduction (Oxford, England). 2003;18(4):885-887.
  7. Rhee SH, Waldman ID. Etiology of sex differences in the prevalence of ADHD: an examination of inattention and hyperactivity-impulsivity. American journal of medical genetics Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics. 2004;127b(1):60-64.
  8. Baio J, Wiggins L, Christensen DL, et al. Prevalence of Autism Spectrum Disorder Among Children Aged 8 Years – Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2014. Morbidity and mortality weekly report Surveillance summaries (Washington, DC : 2002). 2018;67(6):1-23.