To the Editor: Dr McTiernan and colleagues1 of the Women's Health Initiative (WHI) reported
that increased physical activity was associated with a 14% decrease in the
risk of breast cancer in postmenopausal women. These results were not based
on a randomized trial of exercise vs no exercise, but rather were from observational
data. An earlier randomized WHI study2 of
estrogen plus progesterone therapy vs placebo demonstrated that the prior
observational studies that had demonstrated a cardiovascular benefit for hormone
therapy were incorrect. It was clear that there was a strong bias in the prior
observational studies toward showing a cardiovascular benefit in the women
who had selected the hormone replacement therapy intervention. Thus, it is
possible that a similar bias occurred in this study as well.
Burke HB. Increasing Rates of Forearm Fractures in Children—Reply. JAMA. 2003;290(24):3193. doi:10.1001/jama.290.24.3193-a
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