Vitamin A, Vitamin D and Osteoporosis Reprise

Chris Masterjohn just pointed out a new study that examined the relationship of vitamin A to osteoporosis in the context of vitamin D intake. The study is part of the massive Women's Health Initiative, which involved over 75,000 women. The conclusion:

No association between vitamin A or retinol intake and the risk of hip or total fractures was observed in postmenopausal women. Only a modest increase in total fracture risk with high vitamin A and retinol intakes was observed in the low vitamin D-intake group.

In other words, only women with a low vitamin D intake (less than 440 IU per day) had an increased likelihood of fracture at high vitamin A intakes (more than 8,000 IU per day). This is consistent with the hypothesis that an above-average intake of vitamin A only increases the risk of osteoporosis in the presence of low vitamin D, and that vitamin D deficiency, not vitamin A excess, is the true problem. Hop over to Chris's post for more details.

Vitamin A on Trial: Does Vitamin A Cause Osteoporosis?
Is Vitamin A Toxicity a Concern?