calcium. The exception is Trivedi et al. (2003), which examined vitamin D supplementation and fracture risk in a population of men and women of average age 75 years. In any case, interpretation of these data is complicated by the unknowns surrounding the background intake of vitamin D over and above the supplemented dose.
The large study (n = 2,686) carried out by Trivedi et al. (2003) included more men than women (suggesting that the included population was actually at lower risk for fracture than would have been the case if the study had focused predominantly on women) and was longitudinal (5 years), including repeat measures on the same individual. The amount of vitamin D used for treatment was the equivalent of 800 IU/day, although it was administered as a 100,000 IU dose every 4 months for the duration of the study. Although this may limit somewhat the applicability of the study for DRI purposes, it is not as large as the 500,000 IU dose once yearly used by others (e.g., Sanders et al., 2010). Under these circumstances, the work of Trivedi et al. (2003) is helpful in taking uncertainty into account.
The reason not to dismiss the effect of 800 IU of vitamin D per day as an aberration because of a lack of dose–response data, even in the face of data generally not supportive of an effect of vitamin D alone regarding reduced fracture risk for the oldest adults, is that persons more than 70 years are a very diverse group. This group is undergoing a number of physiological changes with aging that could have an impact on and increase the variability around an average requirement, particularly in light of the known and high variability of these physiological changes among aging individuals. If this is assumed to be the case, then it is likely that the