Vitamin A intake and the risk of hip fracture in postmenopausal women: the Iowa Women’s Health Study

Prospective cohort study (Iowa Women's Health Study). 34,703 postmenopausal women aged 55–69 at baseline; predominantly white; baseline questionnaire in 1986; follow-up through 1997; self-reported hip and nonhip fractures; vitamin A exposure assessed from foods and supplements via semiquantitative FFQ.

Vitamin A-containing dietary supplements; baseline exposure; intake from supplements categorized as <5,000 IU, 5,000–9,999 IU, or ≥10,000 IU; taken orally; follow-up duration about 9.5 years.

Supplement users had a 1.18-fold higher risk of incident hip fracture vs nonusers after adjustment (RR 1.18, 95% CI 0.99–1.41); no increased risk of all fractures (RR 1.00, 95% CI 0.95–1.05). No dose–response relationship for vitamin A or retinol from supplements; no association between total vitamin A or retinol intake and hip or all fractures. Among nonusers, higher intake of food-derived vitamin A was associated with fewer all fractures (p for trend = 0.01). Conclusion: little evidence that higher vitamin A or retinol intake increases hip or all fracture risk in this cohort; any observed increase with supplements is small and not dose-responsive.

Vitamin A intake measured only at baseline with a semiquantitative FFQ; high intraindividual variation and possible exposure misclassification; dietary changes over time not captured; fracture outcomes self-reported; inability to distinguish traumatic vs osteoporotic hip fractures; generalizability limited to predominantly white, older women; potential biases due to loss to follow-up and censoring.