Sweet potatoes, squash, pumpkin, carrots … beta-carotene is easily identified in the rich oranges of fall vegetables -- and is certainly a good force against the evils of free radicals.
Like other antioxidants, beta-carotene has been credited as having disease-preventing powers. Antioxidants destroy harmful free radicals, a natural by-product of the body's metabolic processes.
Cigarette smoking, pollutants, and other chemicals are thought to bump up the number of free radicals, possibly causing some normal cells to turn cancerous. Beta-carotene and other antioxidants are said to "mop up" these free radicals, thus protecting cells and DNA from free-radical damage.
Exactly how beta-carotene supplements could boost cancer risk is not clearly understood. In high-dose supplements, beta-carotene is thought to "convert" from its antioxidant role; instead of destroying free radicals, it may actually increase their production.
Rulings Against Supplements
But don't get confused: Beta-carotene from food sources is outstanding for your health, Susan Taylor Mayne, PhD, professor of epidemiology and public health at Yale University School of Medicine in New Haven, Conn., tells WebMD.
The nutritional supplements, however, are a different matter.
In recent years, some clinical trials have shown that at high doses the supplements may actually increase cancer risk, says Mayne, who helped write the National Academy of Sciences report on Dietary Antioxidants and Related Compounds in 2000.
That committee's ruling: "Based upon current scientific evidence, there was no clear evidence of benefit from beta-carotene supplements -- and that there was even some evidence of adverse effects, particularly in smokers and possibly in drinkers as well," Mayne tells WebMD.
The U.S. Preventive Services Task Force has looked at the top studies and also found no evidence that beta-carotene [supplements] protects against heart disease and cancer -- specifically lung, prostate, colon, breast, or nonmelanoma skin cancer in middle-aged and older adults.
In fact, the Task Force warned against taking beta-carotene nutritional supplements to prevent heart disease and cancer.
Some of the evidence:
Heart disease and stroke: The Cleveland Clinic researchers compiled data from eight trials with follow-up ranging from one to 12 years. Those who took beta-carotene supplements had a small but significant increase in deaths from all causes, including heart disease and stroke. The findings were published June 2003 in The Lancet.
Lung cancer: A study of nearly 29,000 male smokers in Finland showed that those who took a daily beta-carotene nutritional supplement had an 18% higher rate of lung cancer. That study was published in The Journal of the American Medical Association in July 2003.
A study of more than 120,000 people showed that in a 10-year period those who ate the most fruits and vegetables had a 20%-25% lower risk of lung cancer. That study was published in the American Journal of Clinical Nutrition.
Colon Polyps: In a study of 700 people who had a benign polyp removed, those who took beta-carotene nutritional supplements -- and who didn't smoke or drink -- had a marked decrease in colon polyps within the four-year follow-up period.
However, those who smoked or drank alcohol -- and took beta-carotene nutritional supplements -- had a modest increase in recurrence of colon polyps. If they smoked and drank more than one alcoholic drink per day, beta-carotene doubled their risk of polyp recurrence. That study appeared in the May 2003 Journal of the National Cancer Institute.
It may be that at a lower dose, beta-carotene nutritional supplements may have benefits -- that only higher doses are dangerous, says Mayne.
But a better strategy is to eat beta-carotene-rich foods -- such as carrots, oranges, sweet potatoes, squash, yams, apricots, collards, spinach, and mustard greens, she notes.
"Possibly, beta-carotene and other compounds found naturally in food work together to enhance the effectiveness of each other," she tells WebMD.