December 5, 2007
Long-term use of beta-carotene, an antioxidant nutrient found in carrots, sweet potatoes, and cantaloupe, may help to protect the brain against mental decline, a large new study suggests. Men who took high dose beta-carotene supplements for an average of 18 years had modestly sharper memory skills and less cognitive decline than their age-matched peers taking a placebo. The study appeared in the Archives of Internal Medicine, one of the American Medical Association journals.
Long-term cellular damage from "oxidative stress," or exposure to highly reactive oxygen molecules, may be a major factor in cognitive decline. Antioxidants help to fight the effects of oxidation, the same force that turns iron into rust. In the brain, oxidative stress may have a variety of damaging effects, leading to cognitive decline and the eventual onset of Alzheimer's disease.
A number of population studies suggest that a diet rich in antioxidants like vitamin C, vitamin E, and beta-carotene may help to reduce the risk of Alzheimer's. Antioxidant supplements, including beta-carotene, may have additional benefits for the heart and other body systems, some research suggests. However, other studies have been inconclusive.
In the current study, Dr. Francine Grodstein of Brigham and Women's Hospital and Harvard Medical School in Boston, along with colleagues, studied the antioxidant beta-carotene and its effects on cognitive ability in two groups of men. The long-term group included 4,052 men who in 1982 had been randomly assigned to take a dummy placebo pill or 50 milligrams of beta-carotene every other day (equivalent to about 14 times the minimum daily requirement).
Between 1998 and 2001, an additional 1,904 men were randomly assigned to one of the two groups. Both groups were followed through 2003, completing yearly follow-up questionnaires with information about their health and their compliance with taking the pills. The men were assessed by telephone for cognitive function at least once between 1998 and 2002.
The long-term participants had been taking beta-carotene for an average of 18 years, while the short-term group had taken the antioxidant for only a year or so. Men in the short-term group displayed no differences in memory and cognition regardless of whether they took beta-carotene or placebo. But men in the long-term group who took beta-carotene had modestly higher scores on several of the cognitive and memory tests compared with men who took placebo.
"In this generally healthy population, the extent of protection conferred by long-term treatment appeared modest," the authors wrote. "Nonetheless, studies have established that very modest differences in cognition, especially verbal memory, predict substantial differences in eventual risk of dementia."
It must be emphasized, however, that none of the men for whom cognitive testing was reported, in either the beta-carotene or placebo group, were known to have developed Alzheimer's disease or mild cognitive impairment. In other words, the authors studied only the healthy men and did not report whether beta-carotene had any affect on the development of Alzheimer's. This is unfortunate, because one would expect that in the elderly population given cognitive tests, a significant proportion would have developed Alzheimer's.
The authors conclude that, although additional research is needed, the public health impact of long-term beta-carotene use could be large. This is because even small differences in verbal memory may predict risk for later development of Alzheimer's.
Beta carotene is not without risks itself, however. It is highly toxic in large doses. And, it may increase the risk of lung cancer in smokers.
"Thus, the public health value of beta carotene supplementation merits careful evaluation," the authors write. "Moreover, as these data support the possibility of successful interventions at early stages of brain aging in well-functioning subjects, investigations of additional agents that might also provide such neuroprotection should be initiated."
Antioxidant-Rich Fruits and Vegetables
Beta-carotene, a nutrient related to vitamin A, forms the yellow-orange pigment found in fruits and vegetables like carrots and cantaloupe. It belongs to a class of antioxidants known as carotenoids. Green vegetables, such as spinach, broccoli, and lettuce, are also rich in beta-carotene. The darker the green, the higher the beta-carotene content.
Through the years, antioxidants have been held up as a potential preventive against heart disease, cancer, and other ills associated with aging. However, other studies have shown that taking doses that are too high, or focusing on a single nutrient, may potentially promote cancer and have other ill effects.
Given the potential risks of high-dose antioxidant supplements, many nutritional experts recommend that if you take beta-carotene supplements, that it be taken along with other carotenoids, such as lycopene (a possible cancer fighter) and lutein (good for the eyes). Multivitamins and antioxidant mixtures commonly contain beta-carotene along with other antioxidants. A diet rich in colorful fruits and vegetables, such as the Mediterranean diet which also includes fish and heart-healthy fats, may be the best way to get your beta-carotene, some experts say.
"For the clinician, there is no convincing justification to recommend the use of antioxidant dietary supplements to maintain cognitive performance in cognitively normal adults or in those with mild cognitive impairment," writes Dr. Kristine Yaffe, of the University of California, San Francisco, in an editorial accompanying the study. She cites research showing that high doses of beta-carotene or other antioxidants carry risk. However, in the current study, those taking beta-carotene did not have a higher incidence of stroke, heart attack, angina (chest pain) or diabetes. Other diseases were not looked at.
As researchers continue to study the effects of diet and dietary supplements on health and Alzheimer's disease, the best tack may be to eat a varied diet rich in fruits, vegetables, whole grains, and heart-healthy fats. Nuts, fish, and other foods have also all been shown to have brain-boosting benefits. And the earlier you begin to eat a nutrient-rich diet, the better, this and other studies show.
For more on Alzheimer's disease prevention, visit www.ALZinfo.org, the Alzheimer's information site.
Francine Grodstein, ScD; Jae H. Kang, ScD: Robert J. Glynn, PhD; et al: "A Randomized Trial of Beta Carotene Supplementation and Cognitive Function in Men: The Physicians; Health Study II." Archives of Internal Medicine, Volume 167, Number 20, pages 2184-2190.
Kristine Yaffe, MD: "Antioxidants and Prevention of Cognitive Decline: Does Duration of Use Matter?" (editorial). Archives of Internal Medicine, Volume 167, Number 20, pages 2167-2168.