Dietary Iron Positively Influences Bone Mineral Density in Postmenopausal Women on Hormone Replacement Therapy

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Abstract
The associations of dietary intakes of iron and calcium on change in bone mineral density (BMD) were examined over 1 y in healthy nonsmoking postmenopausal women (mean age 55.6 ± 4.6 y) stratified by hormone replacement therapy (HRT) use (HRT, n = 116; no HRT, n = 112). BMD was measured at lumbar spine L2–L4, trochanter, femur neck, Ward's triangle, and total body using dual-energy X-ray absorptiometry at baseline and 1 y. Mean nutrient intakes were assessed using 8-d diet records. All women received 800 mg/d of supplemental elemental calcium. Regression analyses examined the effects of iron and calcium intakes on BMD change adjusting for years past menopause, baseline BMD, weight change, exercise, and energy intake. The interaction of iron with calcium on BMD change was assessed using tertiles of iron and calcium intake and estimated marginal mean change in BMD. Iron was associated (P ≤ 0.05) with greater positive BMD change at the trochanter and Ward's triangle in women using HRT. Calcium was associated (P ≤ 0.05) with BMD change at the trochanter and femur neck for women not using HRT. In women using HRT in the lowest tertile of calcium intake, change in femur neck BMD increased linearly as iron intake increased. In women not using HRT, BMD increased in the women in the highest tertile of calcium intake. We conclude that HRT use appears to influence the associations of iron and calcium on change in BMD.