Dr. Elisabeth J. Johnson, Tufts University, US Department of Agriculture Human Nutrition Research Center on Aging, Boston, USA.
" Cognitive decline in the elderly is a significant public health issue. It has been estimated that the incidence of mild cognitive impairment is 19 percent in those younger than 75 years to 29 percent in those older than 85 years. Further, 13 percent of people aged 65 years and older are afflicted with Alzheimer’s disease (1). These figures are likely to increase given that the number of people over 65 years is rising. As with most age-related diseases, the most cost-effective way to combat age-related disease is through prevention. One possible strategy is nutrition intervention.
There is growing evidence that oxidative and inflammatory damage contribute to the development of Alzheimer’s disease as well as mild cognitive impairment and age-related cognitive decline (2). An increase in brain oxidative stress is well documented as one of the leading causes of cognitive impairment (3). Accumulated damage to lipid membranes and DNA by free radicals may disrupt normal cell functioning and lead to neuronal death. Given that dietary carotenoids function as both antioxidants and anti-inflammatory agents, intake of these dietary components may hold promise in cognitive health for the elderly.
Fruits and vegetables are major dietary sources of carotenoids, which have the ability to trap free radicals enabling them to prevent lipid damaging effects (4). Research has shown that patients with mild cognitive impairment had decreased plasma levels of antioxidants, including carotenoids (5). Additionally, a higher carotenoid status has been reported to be related to lower concentrations of markers on inflammation (6).
The results from epidemiological studies on the relationship between beta-carotene and cognitive functioning have been inconsistent. Both dietary intake and serum levels of beta-carotene have been associated with measures of cognitive function in some (7, 8), but not all studies (9). Two randomized clinical trials also found evidence of beta-carotene protection against cognitive decline. In the Physician’s Health Study, men treated with 50 mg of beta-carotene every other day for an average of 18 years had higher global cognitive and verbal memory scores compared with men on placebo. However, there was no effect in men receiving just one year of supplementation (10). In a randomized trial of women with cardiovascular disease, there was no effect on cognitive decline after 10 years of beta-carotene treatment, although beta-carotene supplementation was effective in slowing cognitive decline in a subgroup of women who had low dietary intakes of beta-carotene (11). Thus, it appears that beta-carotene supplementation may be protective against cognitive decline but this may be dependent on duration of supplementation and initial beta-carotene status. One possible explanation of the failure to detect an association in the epidemiologic studies is that the dietary assessment methods for beta-carotene intake may not provide sufficiently accurate measures of actual intake over the long-term.
Although much recent work has focused on lutein and zeaxanthin and their role in eye health, lutein and zeaxanthin are also the dominant carotenoids in various brain regions. Both carotenoids are likely to have protective effects in the brain and may also influence interneuronal communication and function via multiple mechanisms. In two large cohort studies, consumption of vegetables—particularly the green leafy variety that are rich sources of lutein and zeaxanthin—was associated with slower rates of cognitive decline (12, 13). Plasma antioxidants, particularly lutein and zeaxanthin, were shown to be related to improved cognitive function in healthy seniors and are depleted in both individuals with mild cognitive impairment (14) and those with Alzheimer’s disease (5). Other evidence suggests that lutein supplementation, alone or in combination with docosahexaenoic acid, may be able to improve certain aspects of cognitive performance in healthy older women (15). While far from conclusive, the idea that lutein and zeaxanthin can influence cognitive function is certainly feasible.
In conclusion, evidence to date suggests that dietary carotenoids may be beneficial in cognitive health. This may be due to their role as antioxidants. Low levels of carotenoids may precede or be a consequence of cognitive impairment. That is, poor carotenoid intake may be a risk factor for poor cognitive performance. The elderly may be at particular risk for poor nutrition. The determination of a role for carotenoids in cognitive health requires longitudinal epidemiological studies and clinical trials with carotenoids supplementation.”
Agro FOOD, 21(4), July 2010