Children with higher levels of two types of 25-hydroxyvitamin D (25(OH)D) do not appear to fare better in school, researchers found.

Increased levels of 25(OH)D3 were not associated with any academic outcomes at ages 13 to 14 or 15 to 16, according to Debbie Lawlor, MBChB, PhD, of the University of Bristol in England, and colleagues.

And higher levels of 25(OH)D2 unexpectedly were associated with worse academic performance at both ages, although that could have been a chance finding, the researchers reported online in the Journal of Epidemiology & Community Health.

“The increasing number of association studies suggesting that low levels of vitamin D are related to a wide range of health outcomes, including cognitive function, have resulted in calls for changes to public health guidance regarding extreme protection against UV exposure,” they wrote.

“However,” they continued, “our results suggest that protection of children from UVB exposure, which has been associated with low levels of vitamin D, but which protects against skin damage and skin cancer, is unlikely to have any detrimental effect on academic achievement.”

Most studies in adults have identified a positive relationship between serum levels of 25(OH)D and cognitive function, whereas two studies in children have not supported such an association. There remains some question about whether the different forms of 25(OH)D are interchangeable when doing studies such as these.

To explore the issue, Lawlor and colleagues turned to the Avon Longitudinal Study of Parents and Children (ALSPAC). The current analysis included 3,171 children who had measures of 25(OH)D3 and 25(OH)D2 taken at an average age of 9.8.

Academic performance at age 13 to 14 was based on total scores in English, math, and science. At age 15 to 16, the assessment was based on performance on General Certificates of Education exams in a range of subjects.

Consistent with the two previous studies in children, which used data from the National Health and Nutrition Examination Survey (NHANES), serum 25(OH)D3 concentrations were not associated with any academic outcomes.

“It is possible that the positive association of 25(OH)D with cognitive function seen in adults does not emerge until later in life or that the results from previous cross-sectional adult studies are due to reverse causality,” the authors wrote.

Higher serum 25(OH)D2 concentrations were associated with worse performance in English at age 13 to 14, as well as a lower likelihood of achieving at least 5 A to C grades at age 15 to 16 (OR 0.91, 95% CI 0.82 to 1.00).

Those findings were unexpected and should be validated in future studies, according to the researchers.

“This association was consistent with the associations of indicators of lower socioeconomic position (e.g., eligibility for free school meals, lower parental education, and socioeconomic position) with lower educational attainment and higher 25(OH)D2 concentrations,” they wrote. “It is therefore possible that it represents residual confounding.”

The authors acknowledged that the study was limited by the uncertain generalizability to populations with different dietary intakes or UVB exposures, the use of academic performance rather than standardized tests of cognitive function, and the use of single measurements of 25(OH)D levels.

Primary source: Journal of Epidemiology & Community Health

Source reference: Tolppanen A-M, et al “Association of serum 25-hydroxyvitamin D3 and D2 with academic performance in childhood: findings from a prospective birth cohort” J Epidemiol Community Health 2012; DOI: 10.1136/jech-2011-200114.