Vitamin A intake and osteoporosis: a clinical review.
If osteoporosis is linked with vitamin A (Vit A) A consumption, millions of people could be affected. A MEDLINE search was performed with keywords retinol, beta-carotene, and osteoporosis. Of 20 clinical studies, 3 were randomized controlled trials (RCTs), 14 were observational studies, and 3 were case reports. Most (8) observational studies were cross-sectional. Oral retinoyl palmitate (RP) in high doses induces fractures and radiographic osteoporosis in animals. Retinol intake from diet or supplements is negatively associated with lumbar, femoral neck, and trochanter bone mineral density (BMD). There is a graded increase in relative risk of hip fracture with increasing retinol intake, attributable primarily to retinol (either from diet or supplements) but not beta-carotene intake. Higher serum retinol levels are associated with higher risk of any fracture and with higher risk of hip fracture, whereas there is no evidence of harm associated with beta-carotene intake. The few RCTs involve serum markers of bone metabolism, not bone density or fracture outcomes. Observational studies are generally consistent in finding harm from either dietary or supplemental retinol intake on BMD and hip fracture risk. Total Vit A intake is more important than source in determining harm. Adverse effects may occur at a level of retinol intake that is only about twice the current recommendation for adult females.
It is not yet possible to set a specific level of retinol intake above which bone health is compromised. Pending further investigation, Vit A supplements should not be used with the express goal of improving bone health.
J Womens Health (Larchmt) Oct 2004
The recommended dietary allowance (RDA) for Vitamin as preformed Vitamin A (Retinol Activity Equivalents) is 700 mcg (or 2,333 IU). This article suggests that twice that, or 4666 IU, increases fracture risk.