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UK adolescents lack vitamin D, study shows

Adolescents need between 10 and 30 µg/day vitamin D

Ingrid Torjesen

Thursday, 20 October 2016

High levels of vitamin D insufficiency have been shown in UK adolescents, by a study,* published in the American Journal of Clinical Nutrition, which has for the first time identified the intake needed by adolescents in order to maintain adequate serum vitamin D levels during the winter.

Adolescents are particularly vulnerable to vitamin D insufficiency, and previous studies have shown that vitamin D levels decrease during puberty. Adolescents are less likely to spend time outdoors than younger children, so experience less exposure to the sun, which is how we naturally obtain vitamin D. Since most rapid bone growth occurs during the adolescent years, it is vital that teenagers have sufficient levels of vitamin D in order to achieve peak bone mass by late adolescence. This is thought to help reduce age-related bone loss in later life.

For the study, conducted by researchers from the University of Surrey's Department of Nutritional Sciences in collaboration with the University of Copenhagen and University College Cork, 110 white male and female adolescents were given varying levels of vitamin D supplements, while some were given a placebo supplement, for a 20-week period during winter.

The results showed that mean ± SD serum 25(OH)D concentrations increased from 49.2 ± 12.0 to 56.6 ± 12.4 nmol/L and from 51.7 ± 13.4 to 63.9 ± 10.6 nmol/L in the 10- and 20-μg/d groups, respectively, and decreased in the placebo group from 46.8 ± 11.4 to 30.7 ± 8.6 nmol/L.

Vitamin D intakes required to maintain 25(OH)D concentrations >25 and >30 nmol/L in 97.5% of adolescents were estimated to be 10.1 and 13.1 μg/d, respectively, and 6.6 μg/d to maintain 50% of adolescents at concentrations >40 nmol/L. Because the response of 25(OH)D reached a plateau at 46 nmol/L, there is uncertainty in estimating the vitamin D intake required to maintain 25(OH)D concentrations >50 nmol/L in 97.5% of adolescents, but it exceeded 30 μg/d.

The researchers concluded that vitamin D intakes of between 10 and approximately 30 µg/day are required to maintain an adequate level of vitamin D and avoid vitamin D deficiency.

The study forms part of a four-year EU-funded project, ODIN, which aims to investigate safe and effective ways of improving dietary vitamin D intakes through food fortification and bio-fortification.

Researcher Dr Taryn Smith said: "The research has found that adolescence, the time when bone growth is most important in laying down the foundations for later life, is a time when vitamin D levels are inadequate. The ODIN project is investigating ways of improving vitamin D intake through the diet - and since it is difficult to obtain vitamin D intakes of over 10 ug/day from food sources alone, it is looking at ways of fortifying our food to improve the vitamin D levels of the UK population as a whole."

* Smith T J, et al. Estimation of the dietary requirement for vitamin D in adolescents aged 14–18 y: a dose-response, double-blind, randomized placebo-controlled trial. Am J Clin Nutr ajcn138065; First published online September 21, 2016. doi: 10.3945/​ajcn.116.138065

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