The antioxidant β-carotene does not improve cognitive performance among healthy older men in the short term, according to a subgroup analysis of data from a longitudinal study.
These findings add to the growing list of study results concluding that counteracting long-term oxidative stress with antioxidants doesn't appear to protect against cognitive decline. However, it is still possible that long-term treatment with β-carotene may confer “modest” neuroprotection, reported Francine Grodstein, Sc.D., and her associates in the Physicians' Health Study (PHS) II.
The PHS II is an ancillary study of the Physicians' Health Study, a randomized clinical trial assessing whether vitamin supplements prevent cancer and cardiovascular disease. Cognitive evaluations were added to the trial to assess any cognitive impact of supplementation. The PHS II study extended the follow-up on a subgroup of 7,641 male physicians (average age 73 years) from 1997 through 2003, and also added 7,000 new recruits aged 55 and older in 1998–2001.
Dr. Grodstein and her coinvestigators assessed cognitive outcomes for 2,989 subjects who took placebo and 2,967 subjects who took β-carotene for various durations that ranged from 2 months to 20 years. Verbal memory, immediate and delayed recall, category fluency, and mental state were assessed.
β-Carotene yielded no cognitive benefits in subjects who had taken it for 3 years or less, according to Dr. Grodstein of Harvard School of Public Health, Boston, and her associates.
However, subjects who had taken β-carotene for at least 15 years showed better scores on several cognitive measures than did those who had taken placebo. “In general, the effect of long-term beta carotene treatment was comparable to delaying cognitive aging by 1 to 1.5 years,” the researchers said (Arch. Intern. Med. 2007;167:2184–90).
Nevertheless, in a subset of 4,074 subjects who had further cognitive assessments 2–4 years later, these differences were found to be not statistically significant.
Regarding this last finding, Dr. Kristine Yaffe of the University of California, San Francisco, said in an editorial accompanying this report, “it is curious that the authors minimize the results for approximately 4,000 men who had repeated cognitive testing.”
Dr. Yaffe noted that “several trials have examined relatively long durations of antioxidant exposure (up to 10 years) and failed to find an effect of treatment on cognitive outcomes” (Arch. Intern. Med. 2007;167:2167–8).
“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. Furthermore, there is new concern that high-dose antioxidant supplementation, including beta carotene, may have adverse health consequences including mortality,” Dr. Yaffe said.
β-Carotene had no benefit for those taking it less than 3 years. ©photo-Dave/Fotolia.com