Beta-carotene is the most widely used supplement in the treatment of leukoplakia. In a clinical trial of betel nut chewers with leukoplakia, supplementation with 150,000 IU of beta-carotene twice per week for six months significantly increased the remission rate compared with placebo (14.8% vs. 3.0%). The effectiveness of beta-carotene for treating leukoplakia was also confirmed in a double-blind trial that used 100,000 IU per day for six months. In one trial, supplementation with 33, 333 IU of beta-carotene per day, alone or combined with 50 IU of vitamin E, was reported not to reduce the incidence of leukoplakia. These results have also been observed in smaller trials.
Drug therapy with a synthetic, prescription form of vitamin A (known as Accutane, isotretinoin, and 13-cis retinoic acid) has been reported to be more effective than treatment with 50,000 IU per day of beta-carotene. However, because of the potential toxicity of the vitamin A-like drug, it may be preferable to treat leukoplakia with beta-carotene, which is much safer.
Before the research on beta-carotene was published, vitamin A was used to treat leukoplakia. One group of researchers reported that vitamin A (28,500 IU per day) was more effective than beta-carotene in treating people with leukoplakia. Another trial found that the combination of 150,000 IU per week of beta-carotene plus 100,000 IU per week of vitamin A led to a significant increase in remission time compared to beta carotene alone in betel nut chewers. Women who are or who could become pregnant should not take 100,000 IU of vitamin A per week without medical supervision.
Lung Cancer in Nonsmokers
In double-blind trials, synthetic beta-carotene supplementation has led to an increased risk of lung cancer in smokers, though not in groups consisting primarily of nonsmokers. Smokers should avoid synthetic beta-carotene supplements, including the relatively small amounts found in many multivitamins.
The researchers who conducted the lung cancer trials have been criticized for not having used the natural form of beta-carotene. Preliminary evidence suggests that natural beta-carotene supplementation results in better antioxidant activity and anticancer activity in humans than does supplementation with synthetic beta-carotene. Nonetheless, much less is known about natural beta-carotene and questions remain about its potential efficacy. The effect of natural beta-carotene supplementation on lung cancer risk has yet to be studied.
The strong association between increased intake of beta-carotene from food and a reduced risk of lung cancer does not necessarily mean that supplementation with natural beta-carotene supplements would reduce the risk of lung cancer. Dietary beta-carotene may be a marker for diets high in certain fruits and vegetables that contain other anticancer substances that may be responsible for the protective effects. Until more is known, some doctors advise smokers to avoid all forms of beta-carotene supplementation—even natural beta-carotene.
Night blindness may be an early sign of vitamin A deficiency. Such a deficiency may result from diets low in animal foods (the main source of vitamin A), such as eggs, dairy products, organ meats, and some fish. Low intake of fruits and vegetables containing beta-carotene, which the body converts into vitamin A, may also contribute to a vitamin A deficiency. Doctors often recommend 10,000 to 25,000 IU of vitamin A per day to correct a deficiency. Beta-carotene is less effective at correcting vitamin A deficiency than is vitamin A itself, because it is not absorbed as well and is only slowly converted by the body into vitamin A.
Years ago, researchers theorized that beta-carotene in skin might help protect against sensitivity to ultraviolet light from the sun. Large amounts of beta-carotene (up to 300,000 IU per day for at least several months) have allowed people with photosensitivity to stay out in the sun several times longer than they otherwise could tolerate. The protective effect appears to result from beta-carotene’s ability to protect against free-radical damage caused by sunlight.
Caution: Synthetic beta-carotene has been linked to increased risk of lung cancer in smokers. Until more is known, smokers should avoid all beta-carotene supplements.