Dietary caffeine acutely increases urinary calcium loss (1), and these losses are not entirely compensated for in the 24 h after caffeine consumption (2). Overall, the evidence indicates that younger individuals can increase their calcium absorption to compensate for the urinary losses, whereas the elderly are less adaptable (3). It is not surprising that most cross-sectional studies of elderly populations showed no association of caffeine consumption with bone loss or bone mineral density because so many genetic and lifestyle factors are now known to affect bone health. Previous prospective studies of elderly populations yielded conflicting results regarding caffeine and bone loss. Although Cummings et al (4) included caffeine consumption among the risk factors for hip fracture, Lloyd et al (5) were unable to find any association of caffeine with bone loss in a 2-y prospective study of 112 postmenopausal women. Similarly, Hannan et al (6) did not find that caffeine (or calcium intake) was associated with bone loss in the Framingham study population.
The interaction of caffeine intake with calcium on bone loss was reported by Harris and Dawson-Hughes (7). These investigators found that bone loss from the spine and total-body bone mineral density occurred only in postmenopausal women who had both low calcium intakes (440–744 mg/d) and high caffeine intakes (450–1120 mg/d). The following year, this same research team showed that response to calcium supplementation is influenced by vitamin D receptor gene (VDR) genotype (8), with the rate of loss at the femoral neck being reduced by calcium only in the BB VDR subgroup. In retrospect, it is probably not surprising that in this issue of the Journal Rapuri et al (9) report that caffeine's effect on bone loss is also associated with VDR genotype.