Based on new research, smokers may want to check the beta-carotene content of any multivitamin supplements they are taking, especially if these supplements are promoted as being beneficial for eye health.

There’s strong evidence that high dose beta-carotene can boost smokers’ lung cancer risk, but many multivitamins that contain large amounts of the nutrient carry no warning, Drs. Tawee Tanvetyanon and Gerold Bepler of the H. Lee Moffitt Cancer Center and Research Institute at the University of South Florida in Tampa report in the journal Cancer.

“We need to make the public more aware of this problem,” Tanvetyanon told Reuters Health.

Tanvetyanon and Bepler reviewed all studies of high-dose beta-carotene supplementation and lung cancer risk in the medical literature, and also evaluated the amount of beta-carotene found in dozens of supplements.

Their pooled analysis showed that smokers who took high-dose beta-carotene (from 20 to 30 milligrams daily) had a 24 percent increased risk of lung cancer compared to smokers who weren’t taking beta-carotene. However, the nutrient didn’t affect lung cancer risk for ex-smokers.

Most of the 47 multivitamins the researchers looked at contained 0.3 milligrams of beta-carotene, with amounts ranging from zero to 17.2 milligrams. Among another 17 multivitamins promoted as being beneficial to visual health, most provided 3 milligrams of the nutrient per daily dose, with content ranging from zero to 24 milligrams.

People often take several different multivitamins, Tanvetyanon noted, so even though most products contain relatively small amounts of beta carotene they can add up.

Despite the evidence linking beta-carotene to lung cancer risk for smokers, Tanvetyanon added, many of the products had no warnings on their labels.

“The best warning that I have seen says that if you are a smoker or ex-smoker consult your physician before taking this…but it doesn’t say that this may cause lung cancer, which I think is probably an inadequate disclosure,” the researcher said.

SOURCE: Cancer, July 1, 2008