The current European Community recommended daily amount (EC RDA) of vitamin D is 5µg/d. However, evidence suggests that the current recommendations for vitamin D intake are too low and that as a result large numbers of people have poor vitamin D status. Deficiency of 25-hydroxyvitamin D [25(OH)D], the established biomarker for vitamin D, is known to cause rickets in children and osteomalacia in adults, but longer-term less severe deficiency is now associated with diabetes, obesity, cancer and multiple sclerosis. The plasma levels of 25(OH)D should be above ≈40nmol/L in order to prevent vitamin D insufficiency, but optimal levels may be even higher. The deleterious effects of low vitamin D status are particularly apparent during the winter months in high latitude countries, and this problem is exacerbated in those individuals with darker skin, and those who remain indoors for long periods of time during the summer.
Because of the uncertainty about the current recommended intakes of vitamin D, researchers1 have investigated the intake necessary to maintain sufficient 25(OH)D. In a randomised double-blind placebo controlled study, Finnish and Danish girls with a mean age of 11.3y and vitamin D intake of 3.7µg/d were supplemented with 0, 5 or 10µg/d in order to assess levels that were necessary to maintain plasma levels of 25(OH)D above 25, 37.5, 40 and 50nmol/L. The results showed that incremental improvements in plasma 25(OH)D were seen with increased vitamin D intakes, and following winter, the slope of the relationship was 2.43nmol/L per 1µg intake of vitamin D. The vitamin D intake required to maintain plasma levels of 25(OH)D at >25, >37.5, >40 and >50nmol/L in 97.5% of the sample was 8.3, 13.5, 14.5 and 18.6µg/d, and in 50% of the sample was 0.2, 5.3, 6.3 and 10.4µg/d, respectively.
This study shows that in order to maintain a plasma levels of 25(OH)D above ≈40nmol/L by the end of the winter months, intakes of vitamin D of 14.5 µg/d (580iu) are required. This is over 3 times the current EC RDA, and suggests that vitamin D recommendations are inadequate for adolescent girls. Further, the National Diet and Nutritional Survey in the United Kingdom showed that 21% of 11 to 18 year olds had winter serum 25(OH)D levels below 25nmol/L, a level that would put them at risk of developing bone abnormalities. The current recommendations for vitamin D intake are based on obsolete research involving children taking cod liver oil to prevent rickets and therefore the relevance of this research is questionable. Because vitamin D is difficult to obtain in high enough amounts from food, supplements are recommended for those at risk of deficiency.
RdB
