TUESDAY, Sept. 20, 2005 (HealthDay News) -- Whether individuals should take a beta-carotene supplement may depend largely on whether they've ever smoked.
New research confirms findings from past studies that indicate people who have ever smoked -- which means current and former smokers -- who take beta carotene supplements are at an increased risk of tobacco-related cancers.
Conversely, lifetime non-smokers who take beta-carotene supplements enjoy the opposite effect: their cancer risk is lowered.
"We think that the most important finding [of our study] is a lower rate of cancer with increasing beta-carotene consumption in never-smokers, and the highest rate is observed with high beta-carotene in ever-smokers," said study author Dr. Marie-Christine Boutron-Ruault, research director at the Institut national de la sante et de la recherche medicale (INSERM) in France.
"This should encourage people never to start smoking, and if unfortunately, they have smoked, to avoid taking beta-carotene supplements," she said.
Results of the study appear in the Sept. 21 issue of the Journal of the National Cancer Institute.
Beta-carotene is a nutrient found in plants that the body uses to make vitamin A. It's found mainly in deeply colored fruits and vegetables, such as carrots, squash, yams, peaches, apricots, spinach, collard or mustard greens, and broccoli, according to the National Cancer Institute.
Several previous studies have concluded that in smokers, beta-carotene supplements can actually increase the risk of lung cancer.
The new study looked at the incidence of lung cancer, as well as other tobacco-related cancers, such as colorectal, thyroid, ovarian and cervical cancers.
From a group of more than 60,000 French women studied for an average of 7.4 years, 700 women developed cancer known to be associated with smoking. During the study period, the women had been asked about their diets, their use of supplements and their smoking history. Only 2 percent of the women in the study used beta-carotene supplements.
For those with a history of tobacco use, rates of cancer were 368.3 per 10,000 women who had a high intake of beta-carotene, compared to 174 cases per 10,000 for those with a low intake of beta-carotene.
In women who had never smoked, those with the highest intake of beta-carotene enjoyed the lowest risk: 81.7 cases per 10,000, while those with the lowest intake had nearly 182 cases per 10,000 women, according to the study.
Boutron-Ruault said this study didn't look at the reasons why beta-carotene can seemingly protect non-smokers but increase the cancer risk in smokers. However, she said the way cells act in the presence of high levels of beta-carotene may change when tobacco smoke is also present.
Anyone who has smoked in the past should avoid taking beta-carotene supplements, which may also be found in some multi-vitamins, the study authors pointed out. But they don't believe that former or current smokers should be concerned about beta-carotene consumption from their diets.
"Although beta-carotene may act as a carcinogen, there is no evidence that smokers should avoid consuming beta-carotene rich foods such as fruits and vegetables, in which other components, such as vitamin C and E, may counteract a potentially deleterious interaction of beta-carotene with smoking," the authors wrote.
Karen Collins, a registered dietician and nutrition advisor to the American Institute for Cancer Research, agreed that anyone who has ever smoked should continue to eat a varied diet that includes fruits and vegetables containing beta-carotene.
"You don't absorb anywhere near the amount of beta-carotene from food that you do from supplements," Collins said.
"I would strongly encourage everyone to eat an abundance of fruits and vegetables," she added.
And for those who've never smoked, Collins said you can get plenty of beta -naturally by consuming the recommended five to nine servings of fruits and vegetables daily.
"Seven, eight, nine servings a day substantially lowers the risk of cancer without jumping to supplements," she said. If you're not getting that much from your diet, Collins added, "you need to look at supplements and their potential benefit for non-smokers."
To learn more about earlier trials on beta carotene in smokers, visit the National Cancer Institute.