What's Wrong with Beta-Carotene and Vitamin A Supplements?
I do not recommend taking supplements that contain vitamin A or beta-carotene as an isolated carotenoid because there are risks associated with consumption of these nutrients above what we receive in our diet from foods. Ingesting vitamin A or isolated beta-carotene in the form of supplements may interfere with the absorption of other crucially important carotenoids, such as lutein and lycopene, thus potentially increasing cancer risk.1-6
Isolated Beta-Carotene Associated with Increased Cancer Risk
The precursor to vitamin A, beta-carotene was once regarded as a safe and beneficial antioxidant and even recommended as an “anti-cancer vitamin,” but more recently it has been shown to increase the risk of certain cancers when administered as an isolated carotenoid supplement. Scientists now suspect that problems may result when beta-carotene is ingested without other carotenoids that would have been present had it been ingested from real food. Beta-carotene is only one of about 600 carotenoids that exist. Beta-carotene supplements are poor substitutes for the broad assortment of carotenoid compounds found in plants.
Researchers thought that beta-carotene had a powerful anti-cancer effect because they had found that populations with high levels of beta-carotene in their bloodstream had exceedingly low rates of cancer. Recently, it was discovered that the reason these people were protected against cancer was because of hundreds of carotenoids and phytochemicals in the fruits and vegetables they were consuming. It wasn't that beta-carotene alone was responsible for the benefit; it was merely that it had served as a flag or marker for those populations with a high fruit and vegetable intake. Unfortunately, many scientists confused the flag for the ship.
In Finnish trials, using beta-carotene supplements failed to prevent lung cancer, and there was actually an increase in cancer in those who took the supplement. This study was halted when the physician researchers discovered the death rate from lung cancer was 28 percent higher among participants who had taken the high amounts of beta-carotene and vitamin A. The death rate from heart disease was also 17 percent higher in those who had taken the supplements compared to those just given a placebo.2 Another recent study showed similar results, correlating beta-carotene supplementation with an increased occurrence of prostate cancer. Furthermore, a meta-analysis of antioxidant vitamin supplementation found that beta-carotene supplementation was associated with increased all-cause mortality rate.6
As a result of these European studies, as well as similar studies conducted here in the United States, articles in the New England Journal of Medicine,3 the Journal of the National Cancer Institute,4 and the Lancet5 all have advised people to stop taking beta-carotene supplements.
Vitamin A Poses Even Greater Risk
Yes, taking extra vitamin A (retinyl palmitate and retinyl acetate) may be even more risky than taking supplemental beta-carotene. Since beta-carotene gets converted into vitamin A by your body, there is no reason a person eating a reasonably healthy diet should require any extra vitamin A. There is solid research revealing that supplemental vitamin A induces calcium loss in the urine, contributing to osteoporosis. Too much vitamin A is known to be toxic to the liver, and can cause birth defects. The most common effect of toxic doses of vitamin A in animals is spontaneous fracture.
In humans, excess vitamin A is potentially a problem, even in ranges not normally considered toxic.7 One study found that subjects with a vitamin A intake in the range of 1.5 mg had double the hip fracture rate of those with an intake in that range of 0.5 mg.8 For every 1 mg increase in vitamin A consumption, hip fracture rate increased by 68%. Vitamin A supplementation has also been associated with a 16% increase in all-cause mortality in a meta-analysis of many supplementation studies.6
1. Mayne ST: Beta-carotene, carotenoids, and disease prevention in humans. FASEB J 1996;10:690-701.
2. Omenn GS, Goodman GE, Thornquist MD, et al: Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med 1996;334:1150-1155.
3. Hennekens CH, Buring JE, Manson JE, et al: Lack of effect of long-term supplementation with beta carotene on the incidence of malignant neoplasms and cardiovascular disease. N Engl J Med 1996;334:1145-1149.
4. Albanes D, Heinonen OP, Taylor PR, et al: Alpha-Tocopherol and beta-carotene supplements and lung cancer incidence in the alpha-tocopherol, beta-carotene cancer prevention study: effects of base-line characteristics and study compliance. J Natl Cancer Inst 1996;88:1560-1570.
5. Rapola JM, Virtamo J, Ripatti S, et al: Randomised trial of alpha-tocopherol and beta-carotene supplements on incidence of major coronary events in men with previous myocardial infarction. Lancet 1997;349:1715-1720.
6. Bjelakovic G, Nikolova D, Gluud LL, et al: Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev 2008:CD007176.
7. Whiting SJ, Lemke B: Excess retinol intake may explain the high incidence of osteoporosis in northern Europe. Nutr Rev 1999;57:192-195.
8. Melhus H, Michaelsson K, Kindmark A, et al: Excessive dietary intake of vitamin A is associated with reduced bone mineral density and increased risk for hip fracture. Ann Intern Med 1998;129:770-778.