Researchers say dietary supplementation and physical activity is unlikely to protect against cognitive decline.
The two randomized controlled studies published in the journal JAMA have tested the influence of lifestyle interventions on cognitive outcomes, with over 5,800 people taking part.
While they "failed to demonstrate significant cognitive benefits, these results should not lead to nihilism involving lifestyle factors in older adults," concludes an editorial accompanying the studies in the same issue of the journal.
The diet study concludes: "Among older persons with age-related macular degeneration, oral supplementation with long-chain polyunsaturated fatty acids or lutein/zeaxanthin had no statistically significant effect on cognitive function."
The exercise study concludes: "Among sedentary older adults, a 24-month moderate-intensity physical activity program compared with a health education program did not result in improvements in global or domain-specific cognitive function."
The editorial article, written by Drs. Sudeep Gill and Dallas Seitz, both from the Queen's University in Ontario, Canada, offers caution:
"It is still likely that lifestyle factors such as diet and physical activity have important roles in the prevention of cognitive decline, dementia, and performance of the activities of daily living."
In the study examining exercise - the Lifestyle Interventions and Independence for Elders (LIFE) study - Dr. Kaycee Sink, of the Wake Forest School of Medicine in Winston-Salem, NC, and colleagues compared a 24-month physical activity program against a health education program to see if it would result in better cognitive function, lower risk of mild cognitive impairment (MCI) or dementia, or both.
Some 1,635 participants aged 70-89 years were randomly assigned to a structured, moderate-intensity physical activity program or a health education program of educational workshops and upper-extremity stretching. The structured exercise involved:
- Resistance training
- Flexibility exercises.
All the older people were sedentary and at risk of mobility disability but able to walk about a quarter of a mile. Measures of cognitive function and incidences of MCI or dementia were determined at 24 months.
The researchers found that the moderate-intensity physical activity did not result in better cognition compared with the health education program.
A significant difference was also lacking between the groups in the incidence of MCI or dementia, although this outcome had limited statistical power. The authors say:
"Cognitive function remained stable over 2 years for all participants. We cannot rule out that both interventions were successful at maintaining cognitive function."
Specifically analyzing the physical activity group aged 80 years or older and those with poorer baseline physical performance, there were better changes in executive function composite scores compared with the health education group.
"This finding is important," say the authors, "because executive function is the most sensitive cognitive domain to exercise interventions, and preserving it is required for independence in instrumental activities of daily living."
Dietary effects may take years
The other study testing the effects of oral supplementation on cognitive function was run by Dr. Emily Chew, from the National Eye Institute at the National Institutes of Health in Bethesda, MD, and colleagues.
Background information from the authors says epidemiological studies have suggested that diets high in omega-3 long-chain polyunsaturated fatty acids (LCPUFAs) have a protective role in maintaining cognitive function. However, numerous randomized clinical trials have failed to show these to be effective in treating dementia.
Participants in the Age-Related Eye Disease Study 2 (AREDS2), who were at risk for developing late age-related macular degeneration (AMD), were randomly assigned to LCPUFAs (1 g) and/or the dietary supplements lutein (10 mg)/zeaxanthin (2 mg) versus placebo.
In addition to annual eye examinations, several cognitive function tests were conducted over the phone at the start and every 2 years of the 5-year study.
There were no statistically significant differences in cognitive function for participants randomized to either group.
The authors speculate that the lack of effect of the supplements was because they were started too late in the aging process and that supplementation over 5 years may not be long enough. They say:
"The process of cognitive decline may occur over decades, thus a short-term supplementation given too late in the disease may not be effective."
Over 4,000 participants underwent cognitive testing and the average age of the participants was 73 years.