The range of vitamin D intakes required to ensure maintenance of wintertime vitamin D status [as defined by incremental cutoffs of serum 25(OH)D] in the vast majority (>97.5%) of 20-40-y-old adults, considering a variety of sun exposure preferences, is between 7.2 and 41.1 microg/d.

To ensure that the vitamin D requirement is met by the vast majority (>97.5%) of adults aged >/=64 y during winter, between 7.9 and 42.8 microg vitamin D/d is required, depending on summer sun exposure and the threshold of adequacy of 25(OH)D. This trial was registered at http://www.controlled-trials.com/ISRCTN20236112 as ISRCTN registration no. ISRCTN20236112.

should be used to assess vitamin D status, as it reflects combined dietary supply and dermal production upon exposure to UV blue (UVB) sunlight (2) . Notwithstanding the importance of on-going discussions with respect to thresholds for serum 25(OH)D that represent adequacy/insufficiency, there is widespread acknowledgement of the presence of vitamin D deficiency in the community and the pressing need to address this deficiency (3) .Taking indicators of bone health, including rickets and osteomalacia, bone mineral density and Ca absorption, for which there was sufficient evidence to provide a reasonable and supportable basis for dietary reference intake (DRI) development, the North American Institute of Medicine (IOM)'s DRI committee for Ca and vitamin D proposed a serum 25(OH)D concentration of 40 nmol/l as the median value above which approximately half the population might meet its vitamin D requirement (and below which half might not) and 50 nmol/l as its estimate of the serum 25(OH)D concentration that would meet the requirement of nearly all (i.e. 97·5 %) normal healthy persons (4) . These serum 25(OH)D concentrations were used to specify estimated average requirement (EAR) values for vitamin D intakes of 400 IU/d (10·0 mg/d) in all age and sex subgroups in the population for more than 1 year, assuming minimal UVB sunlight exposure, and from which RDA values were derived for application to individuals (600 and 800 IU/d (15·0 and 20·0 mg/d) of vitamin D for those aged 1 -70 and 70þ