By Rob Winwood
A 20-week intervention trial (1) of vitamin D has been carried out over the winter months with 110 British adolescents aged 14–18 years as part of the pan-European ODIN (Optimal vitamin D) project. These older teenagers were randomly supplemented with placebo, 10 µg or 20 µg vitamin D per day. These can be considered reasonable levels as the European Food Safety Authority (EFSA) advises 100 µg/d as a tolerable upper intake level for 11 to 17 year olds (2).
Prolonged vitamin D deficiency is known to be detrimental to bone health and leads to rickets and osteomalacia (bone softening) in adults and children respectively (3). Low vitamin D status has been widely reported among people living in the northern latitudes of Europe, particularly during the winter months. It is suggested that adolescents are at risk of low vitamin D levels because they are less likely to be exposed to sunlight than children. This is of concern as bone growth occurs rapidly during teenage years. Vitamin D is essential in ensuring that sufficient calcium is absorbed by bones to enable them to reach peak bone mass. Failure to do so could put them at risk of age-related bone density loss later in life.
Following the intervention, the mean serum 25(OH)D concentrations increased from 49 nmol/L to 52 and 64 nmol/L for the 10.1 µg/d and 20 µg/d groups, respectively. The study authors used this data to calculate that vitamin D intakes of between 10 and 30 µg per day are required during the winter months to maintain serum concentrations above 25 or 50 nmol/L (depending on the threshold level chosen). This agrees well with the UK Scientific Advisory Committee on Nutrition (SACN) recommendation of a requirement of an intake of 10 µg/d to maintain a minimum 25 nmol/L mean serum 25(OH)D concentration (4). The authors believe their study will assist in the ongoing refinement of vitamin D requirements for adolescents (1).