Older women who consume too much vitamin A in food or dietary supplements may be putting themselves at risk for hip fractures, US researchers suggest.
Their national study of more than 72,000 women aged 34 to 77 found that retinol, a potent vitamin A compound, was associated with hip fractures in postmenopausal women over nearly two decades.
There was no significant link between a woman's intake of beta-carotene, a compound that is converted to vitamin A in the body, and hip fracture risk.
Women who took a vitamin A supplement were 40% more likely to experience a hip fracture than women who did not, while women who took multivitamins were 32% more likely to fracture a hip, the investigators found.
Women on hormone replacement therapy were somewhat protected against the effects of too much vitamin A on bones, however.
While vitamin A is necessary for vision, growth, reproduction and a healthy immune system, too much vitamin A has been shown to inhibit the formation of new bone and increase the risk of sustaining fractures.
The findings from the Harvard Medical School in Boston, Massachusetts suggest that levels of retinol in foods that are fortified with vitamin A and in dietary supplements should be re-evaluated.
The recommended dietary intake of vitamin A for women is 700 micrograms per day (mcg/d) with an upper limit set at 3,000 mcg/d, the report indicates.
The study found that multivitamins were the primary source of vitamin A and that liver and fortified milk and breakfast cereals were the main food sources.
About one third of women reported using multivitamins when the study began, compared with more than half of women by the end of the investigation 18 years later.
Basd on the findings from this study, and similar results from others, it's prudent to avoid taking high dose vitamin A supplements unless. Choose a multivitamin supplement with less than 5000 IU vitamin A (retinol). Beta-carotene is considered safe.
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