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TOO MUCH VITAMIN A CAN BE BAD FOR YOUR BONES

(February 2003)

Three reports, two from the United States and one from Sweden, suggest that excessive intake of vitamin A can result in increased risk of osteoporosis and fractures. This would make sense because vitamin A in high doses can decrease bone formation and increase bone resorption, both of which should lead to increasing bone fragility.

The Swedish investigators enrolled 2,322 men, ages 46 to 53 years, and followed them for an average of twenty-four years. Blood retinol levels were determined at enrollment; retinol is the major constituent of vitamin A. During the followup period, there were 266 fractures. The men were divided into five groups (quintiles) according to retinol levels. Those with the highest retinol levels had a 64 percent increased risk of any fracture and a more than doubled risk of hip fracture. Intake of more than 1.5 milligrams of vitamin A daily(that is about 5,000 international units) about doubled fracture risk.

There was no evidence that high blood levels of beta carotene were related to risk of fracture.

The second study is equally intriguing. It is from the Nurses’ Health Study and focused on vitamin A (retinol) and hip fractures occurring over eighteen years in 72,337 female nurses, ages 34 to 77 years at enrollment. During the followup period, 603 hip fractures occurred. The women were divided into five groups (quintiles) according to vitamin A intake from food and supplements; 21 percent of the women had vitamin A intakes above the maximum acceptable level of 3,000 micrograms, about 10,000 international units [IU] a day. Those in the highest intake from food and supplements had a statistically significant 48 percent increase in hip fractures. When the active component of concern in vitamin A, retinol, was analyzed separately, the results were even more impressive.

Consumption of Beta carotene, some of which gets converted to vitamin A in the body, did not increase the risk of hip fracture. Vitamin A supplement use was associated with increased risk as was use of multivitamins. Interestingly, those women who were taking postmenopausal estrogen replacement treatment had no increased risk of hip fracture related to vitamin A intake. The investigators concluded "our 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 (as vitamin A - ed) in fortified foods and vitamin supplements may need to be reassessed since these add significantly to total retinol consumption in the United States".

In the third study, carried out in California, bone density (a measure of bone strength) was measured in 570 older women and 388 older men. Vitamin A supplements were taken by 50 percent of women and 39 percent of men. Bone strength was reduced significantly in those with the greatest vitamin A intake. The negative effect on bones was related to total vitamin A intake (by both food and supplements).

The investigators concluded "in both sexes, increasing retinol (vitamin A) became negatively associated with skeletal health at intakes not far beyond the recommended daily allowance, intakes reached predominantly by supplement users."

Commentary: What does all this mean? First, it should be noted that two older studies did not find a relationship between vitamin A intake and bone fractures. Nevertheless, these three newer studies, together with one done earlier by one of these groups, are quite impressive and their findings are reasonably convergent. The evidence is strong that excessive vitamin A (retinol), but not the vitamin A precursor beta carotene, is bad for the bones, increases the risk for osteoporosis, and the risk of fractures.

Of major concern, two of the three studies found adverse effects on bone at surprisingly low levels of intake. The current recommendation for vitamin A intake is 0.7 to 0.9 milligrams (7,000 to 9,000 micrograms). Vitamin A in foods or supplements is often expressed as international units (IU); 7,000 to 9,000 micrograms is about 2,300 to 3,000 IU. In the three studies, adverse effects on bones (or increased fracture risk) was found at 5,000 IU (two studies) to 10,000 IU (one study).

Of particular interest is the observation that, if postmenopausal women were taking estrogens, no adverse effects of vitamin A on bone were found. This needs confirmation, but it does suggest that young women, who produce lots of estrogens, may be protected against adverse effects of vitamin A on bones.

Although more studies are needed, these studies strongly suggest that, pending more data, we limit vitamin A intake to, at most, 1.5 milligrams (5,000 IU) a day.

The major sources of vitamin A are: liver, fish; milk; other dairy products, including margarines; multivitamins; vitamin A supplements; cod liver oil; and maybe fish oils. On the basis of current information, there is no absolutely definitive recommendation possible, but here are the Healthful Life common sense recommendations:

Finally, there is the BIG question - what about the multivitamins? If a multivitamin includes vitamin A 5,000 IU (as many do), you have to see what percentage of that is beta carotene and subtract; so if 20 percent is beta carotene, subtract one-fifth, leaving 4,000 as vitamin A (retinol). If 5,000 IU is potentially bad for your bones, that one-a-day providing 4,000 IU does not leave you much leeway; for example, two or three glasses of milk plus other dairy foods or certain fish can readily get you into a vitamin A intake range that is potentially damaging to your bones.

Healthful Life believes that, in our present state of knowledge, a multivitamin should probably not contain more than 2,000 IU of vitamin A (retinol) (0.6 milligrams or 600 micrograms). Besides, it is hard to figure out how any more than that in a multivitamin would do you any good.

Of course, a healthy diet with lots of green and yellow vegetables will provide you with plenty of beta carotene; a modest, but significant, percentage of that will be converted by the body to vitamin A.

Michaelsson, K., et al. Serum retinol levels and risk of fracture. The New England Journal of Medicine. Vol 348 (January 23) Pgs 287-294. 2003.

Feskanich, D., et al. Vitamin A intake and hip fractures among postmenopausal women. Journal of the American Medical Association. Vol 287 (January 2) Pgs 47-54. 2002.

Promislow, J.H.E., et al. Retinol intake and bone mineral density in the elderly. Journal of Bone and Mineral Research. Vol 17 (August) Pgs 1349-1358. 2002.