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Vitamin A and Bone Health—What’s the Connection?

Vitamin A and Bone Health—What’s the Connection?

Healthnotes Newswire (September 30, 2004)—Getting too much or too little vitamin A can increase a woman’s chance of breaking a hip, according to a study published in the American Journal of Medicine (2004;117:169–74).

Osteoporosis, a state of diminished bone mass, occurs commonly in postmenopausal women and increases their risk of fracture, particularly at the hips, spine, and wrists. A number of nutritional factors seem to affect loss of bone mass, such as adequate intake of calcium and vitamin D. In addition, a number of other nutrients influence the body’s use of calcium. Recently, the role of vitamin A in calcium metabolism and bone health has been the subject of much research.

Vitamin A is a fat-soluble vitamin found in high amounts in liver, dairy foods, and cod liver oil. It can also be manufactured in the body from beta-carotene, a substance found in many colorful vegetables. Vitamin A deficiency is marked by poor night vision, dry skin, and increased risk of infections and some cancers. Deficiency is also known to cause poor mineralization of bones and high risk of fracture. Recent research has also suggested a link between high vitamin A intake and low bone density. It appears that excess vitamin A in the blood can interfere with the normal depositing of calcium in bone.

The current study examined the data from 2,799 women who answered surveys periodically over as much as 21 years. Blood levels of vitamin A and general use of vitamin supplements were determined initially, and hip fractures were monitored during the study. The women were divided into five categories (quintiles) based on their blood levels of vitamin A. The women in the middle quintile had the fewest hip fractures; women in both the lowest and highest quintiles had nearly twice as many hip fractures as the women in the middle quintile. The percentages of women in each quintile, from lowest to highest, who experienced hip fractures during the study were 7.0%, 5.5%, 4.4%, 6.3%, and 7.9%. Women who used vitamin supplements were more likely to be in the highest blood vitamin A quintile than women who did not.

The results of this study are consistent with those from several other studies that have found a negative effect of both low and high intakes of vitamin A on bone density and risk of fracture. One large study found that women ingesting 10,000 IU (3,000 mcg) of vitamin A per day from food and supplements had a significantly higher risk of hip fracture than women getting 4,166 IU (1,250 mcg) each day. These findings suggest that there is an optimal, moderate level of intake of vitamin A, and intakes both too great and too little might have negative consequences. Not all studies have found that supplementing with vitamin A causes bone loss (see Healthnotes Newswire, September 26, 2002).

It is important to note that none of the studies to date have adequately considered the effects of other dietary factors, including the negative effects of other components of foods rich in vitamin A, on bone mass. (For more on this point see Healthnotes Newswire, January 31, 2002.) For this reason there remains controversy concerning the importance of the findings in the current study. Future research should attempt to clearly distinguish between the effects of vitamin A and other dietary factors, and identify the role of supplemental vitamin A, on changes in bone mass.

Maureen Williams, ND, received her bachelor’s degree from the University of Pennsylvania and her Doctorate of Naturopathic Medicine from Bastyr University in Seattle, WA. She has a private practice in Quechee, VT, and does extensive work with traditional herbal medicine in Guatemala and Honduras. Dr. Williams is a regular contributor to Healthnotes Newswire.

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