The evidence is piling up that too much vitamin A weakens bones and leads to hip fractures. In 2002, Harvard Medical School researchers reported that high vitamin A intake raises the risk for hip fracture in postmenopausal women. The data suggest that the main culprit is retinol, the active form of the vitamin. Retinol is found in supplements, liver, eggs, full-fat dairy products, fish liver oils, and fortified foods such as cereals and skim milk.
Since then, other studies have linked excess retinol to decreased bone strength and greater fracture risk — especially at the hip. The consistency of this evidence suggests that older men and women should consider limiting their retinol-derived vitamin A, particularly from supplements.
A long-term Swedish study found that men with high blood levels of retinol had a risk for hip fracture double that of subjects with average levels. Beta-carotene levels were not associated with increased risk. Also, people whose daily vitamin A consumption was more than 5,000 IU (International Units) per day had a hip fracture risk about double that of participants whose intake was less than 1,666 IU per day.
The study also has meaning for women because they have less bone at midlife and more hip fractures at earlier ages than men do. They also take more supplemental vitamins, the likeliest source of excess vitamin A.
Vitamin A is important for vision, the immune system, and healthy tissues. Although vitamin A deficiency is a leading cause of blindness in developing countries, it's not a major problem in the United States. In this country, health experts worry more about high levels, especially for older people who may have difficulty metabolizing retinol properly.
We know from studies using animals and human cells that excess retinol stimulates cells that break down bone (osteoclasts) and interferes with cells that build new bone (osteoblasts).
Unless you have a health condition involving vitamin A and are under a clinician's care, you may want to take the following precautions:
- Don't take vitamin A supplements.
- When shopping for a multivitamin, look for one that derives part or all of its vitamin A from beta-carotene. If the amounts of retinol and beta-carotene aren't listed on the label, call the manufacturer (many labels display a toll-free number).
- Be aware that the "% Daily Value" of vitamin A listed on food and supplement labels is based on a daily intake of 1,500 mcg (micrograms; 5,000 IU) per day for adults. A scientific panel recently updated the recommended amount, lowering it to 700 mcg (2,330 IU) per day for women. Until we know more, don't exceed 1,500 mcg of retinol from both food and multivitamins.
- Eat lots of colorful vegetables (carrots, spinach, red pepper, tomatoes) and orange fruits (oranges, apricots, peaches). They provide vitamin A from beta-carotene, plus other important nutrients. You can't get too much beta-carotene because it converts to vitamin A only as the body needs it.
New England Journal of Medicine, Jan. 23, 2003
March 2003 update