In Reply: We agree with Dr Hathcock that dietary
guidance must be based on collected evidence from various scientific sources.
With this in mind, we analyzed data from the Nurses' Health Study after a
Swedish study reported that retinol intake was positively associated with
risk of hip fracture and inversely associated with femoral bone mineral density
in women.1 Our finding of a significant
increase in risk of hip fracture with higher retinol intakes in postmenopausal
women was very similar to that observed in the Swedish study. Although we
recognize the inherent limitations of observational research, laboratory data
come with their own strengths and weaknesses. An analysis of data from NHANES
III showed no association between serum retinyl esters and bone mineral density,2 although this finding is difficult to interpret
because there was a single measurement of blood retinyl esters without evidence
that this reflects long-term retinol intake. Also, although bone mineral density
is a major factor in osteoporotic fracture, it is not synonymous with fracture,
which is the outcome of public health concern. The small Icelandic study that
Hathcock cites3 also assessed bone mineral
density rather than fracture and did not control for vitamin D intake, which
confounds the observed effects of retinol.
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