Older women who consume too much vitamin A in food or dietary supplements may be putting themselves at risk for hip fractures.
The 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.
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 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 researchers reviewed dietary information and vitamin use among women enrolled in the Nurses' Health Study, most of whom were white, and divided them into five groups based on their vitamin A intake. Over the next 18 years, women who consumed at least 3,000 mcg/d were 48% more likely to suffer a hip fracture than those who consumed less than 1,250 mcg/d.
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 findings provide further evidence that chronic intake of excessive vitamin A, particularly from retinol, may contribute to the development of osteoporotic hip fractures in women. The amounts of retinol in fortified foods and vitamin supplements may need to be reassessed since these add significantly to total retinol consumption in the United States.
Indeed, the study found that multivitamins were the primary source of retinol 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.
This study serves as a reminder that vitamins are potent, essential nutrients which have effects that can precipitate harm as well as provide benefit. The optimal source is from the foods in our diets, not the dietary supplements often taken to simplify our complex world.
JAMA January 2, 2002;287:47-54, 102-103
In contrast to Dr. Willet's article supporting the use of supplements, there is a flip side.
This study clearly shows that there are potential problems with vitamin supplements. It appears that vitamin A from multivitamin supplements is not very good for bone density.
Vitamin A is the third most common nutrient deficiency in the world. Vitamin A is a family of essential fat soluble dietary compounds that are required for vision, growth, optimized immune function, and cell reproduction.
I strongly suspect this is related to the fact that the vitamin A is in the trans form which is the most potent form of vitamin A but it does not seem to help vision.
Krispin Sullivan, author of a forthcoming book, Naked at Noon, a full chapter on fat soluble vitamins A, D and K related to bone and general health, writes that the reason cod liver oil does not cause a problem is that it contains both A and D. Vitamin A is only safe when vitamin D is adquate and the worldwide insufficiency of vitamin D makes all supplemental vitamin A problematic. One study (J Bone Miner Res 2001 Oct;16(10):1899-905) shows that with sufficient vitamin D no problems with calcium are observed.
Vitamin A is naturally present in the fat of only a few foods, the most concentrated sources are liver, fish liver oils, eggs and whole milk dairy products.
The most important source of dietary vitamin A is liver. Despite its infrequent consumption, liver contributes as much vitamin A to the US diet as that contributed by whole milk and eggs combined. A 3 ounce slice of liver contains 100 times the vitamin A in a glass of whole milk, 116 times that in an egg and 200 times that in a pat of butter. About two thirds of our retinol intake comes from these sources.
The other third comes from the vitamin A precursor, beta-carotene. The most common sources are carrots, tomatoes, vegetable soups, greens, cantaloupe and spinach.
The vitamin A that is in cod liver oil is in the cis form and it is my belief that this is not associated with toxicity. The cis configuration refers to a very specific 3D orientation of the molecule in space. Vitamins are very specific and precise and if the orientation of the molecular bonding is not perfect it will not work.
Take home message:
Most of us should avoid all-purpose multivitamins unless you are guided by an expert in natural health and are using an excellent brand.
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