How can a high intake of preformed vitamin A affect one's bones?

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High intakes of preformed vitamin A may be a health risk for older adults, particularly postmenopausal women at risk of osteoporosis and hip fractures. Preformed vitamin A compounds, whether occurring naturally in foods such as liver or taken as dietary supplements, have been shown to alter bone metabolism. This can lead to bone loss and osteoporosis in humans and laboratory animals. 

Five large-scale population studies in the United States and Sweden found that high dietary intake of vitamin A decreased bone density and increased the risk of hip fracture in both older women and men. These studies prompted the United Kingdom to set a guidance level for vitamin A in adults of 1,500 μg preformed vitamin A per day, half the tolerable upper intake level set for adults. Eating just two snack bars with 50% of the adult daily value of preformed vitamin A would reach this level.

In a long-running study of postmenopausal women 34 to 77 years of age, those who ingested 2,000 micrograms or more of preformed vitamin A per day had nearly twice the rate of hip fractures of those who took less than 500 micrograms a day. Ingesting beta-carotene, a naturally occurring vitamin A precursor, did not contribute significantly to fracture risk.

In animal studies, high dietary intake of vitamin A has been shown to decrease bone mass and lead to bone thinning and spontaneous fractures. Retinoic acid, the active form of vitamin A, inhibits bone formation. Getting enough calcium and vitamin D is important for bone health, but vitamin A counteracts the positive effects of vitamin D.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.