Deeper Dive: Can regular exercise and a good diet attenuate age-associated cognitive decline?

Cognition is a combination of processes in the brain involved with the ability to learn, remember, and make judgements. Health and well being are affected when cognition is impaired. A decline in cognition can range from mild impairment to dementia, which is a form of decline in abilities that is severe enough to interfere with daily activities. The most common form of dementia is Alzheimer’s disease, which affects nearly 6 million people in the United States. Age is the primary risk factor^[1] for cognitive decline. Other risk factors include genetics and lifestyle factors.

There is some scientific evidence^[2] indicating that healthy behaviors may help prevent cognitive decline, although there is not sufficient evidence^[3] to justify encouraging people to adopt specific behaviors for the sole purpose of preventing dementia and cognitive decline. Studies^[4] suggest that aerobic exercise^[5] and resistance exercises^[6] can lessen cognitive decline associated with aging. There are also studies^[7] showing that a healthy diet may help prevent cognitive decline associated with aging. A couple of intervention studies have looked at the combined effects of exercise and a healthy diet on cognition. One study^[8] involving many components, including exercise and a healthy diet, showed that these measures attenuated cognitive decline in middle-aged and older adults with an increased risk of dementia. Another study^[4] showed that aerobic and resistance training alone and combined with a calorie-controlled diet improved cognition in older, obese, frail, and sedentary individuals.

The authors of the study under review point to several systematic reviews and meta-analyses, such as a study looking at aerobic exercise^[9] intended to improve cognitive function in older people without cognitive impairment, a study looking at physical activity^[10] interventions for preventing cognitive decline and Alzheimer-type dementia, and a study looking at the impact of exercise^[11] on the cognitive function of healthy older adults. These reviews concluded that there is a need for long-term randomized controlled trials conducted with large numbers of participants on the effects of aerobic and resistance exercise and a healthy diet on cognitive function. Such information could provide evidence-based recommendations for the general population in an effort to help prevent cognitive decline. To address this gap in the research, the authors conducted this four-year randomized controlled trial to examine whether aerobic or resistance exercise, a healthy diet alone, or combinations of exercise and diet can lessen age-related cognitive decline in a general population of middle-aged and older people.

The risk of cognitive decline increases with aging. It may be possible to decrease this risk through aerobic and/or resistance exercise, a healthy diet, or a combination of these lifestyle factors. This study examined the effects of interventions using these factors on cognitive decline in middle-aged and older people over the course of four years.

The Dose-Response to Exercise Training (DR’s EXTRA) study was a four-year randomized controlled trial examining the health effects of consistent physical exercise and a healthy diet in a random sample of men and women, ages 55–74, living in Kuopio, Finland in 2002. Excluded from the study were people with medical or other conditions that prohibited participation in an exercise intervention, those who could not speak Finnish (and thus were unable to fill out questionnaires), and those with missing data on the Consortium to Establish a Registry for Alzheimer’s Disease^[12] (CERAD). This left 1,401 participants in the study, with 1,199 completing the trial. Data was analyzed using the intention-to-treat principle (i.e., even the participants who dropped out of the study were included in the analysis). Baseline measurements were taken in 2005–2006, two-year measurements were taken between May 2007 and December 2008, and four-year measurements were taken between October 2009 and March 2011. This study was not preregistered.

Figure 1 presents the groups evaluated in this study and a general description of the interventions.

Figure 2: Finnish Nutrition Recommendations in a nutshell

The primary outcome in this study was the four-year change in global cognition as measured by the total score (TS) of the CERAD neuropsychological test (CERAD-TS), including the Mini-Mental State Examination (MMSE). Participants were assessed for cognitive function at baseline, two years, and four years, compliance with exercise over the final 12 months, and/or diet intervention using a one-time four-day food record. All interventions and their possible interactions were analyzed while adjusting for age, gender, years of education, depression symptoms, and waist circumference.

A four-year randomized controlled trial was conducted with 1,401 men and women 57–78 years old. Participants were assigned to one of five groups: resistance exercise, aerobic exercise, diet, combined resistance exercise and diet, combined aerobic exercise and diet, or control group. The exercise goals were at least more than five and two sessions per week of aerobic and resistance exercise, respectively. The dietary goals were in line with Finnish nutrition recommendations and included specific amounts of vegetables, fruits, berries, fish, fiber, and limited saturated fat. The primary outcome was the change in CERAD-TS.

The average participant age was 66.5 years and the mean CERAD-TS and MMSE scores were 82.5 and 27.6 points at baseline, respectively. At baseline, about half of the participants were doing moderate-intensity aerobic exercise for at least 150 minutes per week and most were doing resistance exercise. About 40–54% of the participants reached the recommended intake for fruits, vegetables, berries, fish, and fiber and about 33% ate less than 10% of their diet as saturated fat. In addition, 15% of the participants dropped out during the four-year follow up, with no differences between groups.

Changes in physical exercise included a small increase in frequency of resistance exercise in the resistance exercise group (1.3 times per week) and combined resistance exercise/diet group (1.1 times per week) from baseline to four years; an increase in the duration (47 minutes per week) and volume of aerobic exercise (2.7 MWR-hours per week) in the aerobic exercise group from baseline to four years, and an increase in the duration (31.2 minutes per week) and volume (1.7 MET-hours/week) of exercise in the combined aerobic exercise/diet group from baseline to four years. Participants in all groups involving the diet intervention reached, on average, at least three of their four dietary goals. Participants in the control group either maintained or increased exercise and diet quality. Mean compliance ranged from 47% to 85%. The lowest compliance was observed in the context of resistance exercise in the resistance exercise/diet group and the highest compliance was in diet in the aerobic exercise and diet group. The changes in exercise and nutrition for each group are depicted in Figure 3.

Figure 3: Changes in exercise and nutrition for each group after four years

Aerobic exercise, resistance exercise, or diet alone had no effect on CERAD-TS over the four-year intervention period. The adjusted effects, which were very small, were 0.2 points, 0.5 points, and 0.7 points, respectively. Diet did not potentiate the effect of either of the exercise regimens on CERAD-TS. In the combined aerobic exercise/diet group, there was an increase in CERAD-TS compared to control, where the net increase was 1.4 points with a 95% confidence interval of 0.1–2.7. However, this increase was determined to be statistically insignificant after the authors adjusted for multiple comparisons. There was no effect on CERAD-TS during the first two intervention years from any of the individual interventions and none of the combination interventions had an effect larger than the sum of their individual effects. There were no differences in the changes in subtests of CERAD-TS between any intervention group and the control group. In other words, the interventions did not differ significantly in their generally small effect sizes.

Figure 4: Changes in CERAD-TS over four years compared to control group (with 95% confidence intervals)

Compliance with the interventions ranges from 47% to 85%. There was a trend toward better CERAD-TS over the four-year period in the aerobic exercise/diet group compared to the control group, but the effect was not significant. CERAD-TS changes did not differ across any of the intervention groups. Diet did not potentiate the effect of either of the exercise regimens on CERAD-TS.

This was the first longer term randomized controlled trial to look at a combination of diet and types of exercise on cognition. The main finding of this study was that the combination of a healthy diet (including fruits, vegetables, berries, fish, and fiber and limited saturated fat) and moderate intensity aerobic exercise at least four times per week for 30–60 minutes per session for four years may have led to a small improvement in cognition in middle and older age adults in this study. However, this effect was not quite statistically significant after the authors adjusted for multiple comparisons.

It is important to note that at the baseline of the study, 54% of all participants already reached the current recommendation for at least moderate intensity aerobic exercise of at least 150 minutes per week and about 40–50% of all participants achieved the current recommendation for the consumption of healthy foods. About half the participants complied with the diet and exercise regimens. The combinations of diet/resistance exercise and diet/aerobic exercise, resistance exercise, or diet alone did not affect cognition and there were no significant differences between the effects of the interventions.

Although randomized controlled trials have shown that aerobic exercise alone may be able to improve cognition^[13][14] in older adults, this study did not show a clear change in cognition. The difference in the results of the study may have to do with the duration of the study, supervision-based exercise versus non-supervised exercise in this study, or the fact that more than half of the participants in this study were already physically active and were close to the recommended Finnish diet at the start of the study.

In contrast to the predominantly positive results from studies using aerobic exercise, the results of studies looking at resistance exercise have not been consistent. A 2008 systematic review^[15] concluded that, although beneficial effects of various exercise programs on aspects of cognition have been observed in studies among participants with and without cognitive decline, the majority of the studies did not find any effect. A meta-analysis^[13] conducted in 2017 showed that resistance training, particularly in women, has a positive effect on cognition. Inconsistent findings may be due to different measures of global cognition, compliance, and differences in study populations.

The study under review showed that adherence to the Finnish Nutrition Recommendations showed a 1.2 point increase in CERAD-TS in the diet group over four years. However, this increase was not significantly different from the changes that were observed in the control group. The putative advantages would, however, be in line with observational research on other, more commonly investigated diets: A 2019 review^[7] concluded that current scientific evidence suggests that higher adherence to the Mediterranean, DASH, or MIND diets is associated with less cognitive decline and a lower risk of Alzheimer’s disease, with the strongest associations observed for the MIND^[16] diet. It is possible that dietary patterns (i.e., quantities, varieties, and combinations of foods and beverages) versus intakes of specific food groups or nutrients may be responsible for the beneficial effects on cognition. Although there was no literature found regarding typical cognitive decline specifically over a four-year period, there is some good information^[1] on the effects of aging on cognition.

The strengths of this study included the long duration of intervention (four years) and the large number of participants, as well as the high real-world significance and generalizability of the results due to the inclusion of a sample representing the general population with an age range spanning both middle and older age. Using an intention-to-treat analysis, the authors were able to predict outcomes based on the initial treatment assignment and not on whether the treatment actually took place. Furthermore, the CERAD test, used to assess global cognition, has been shown to have good interrater and test-retest^[12] reliability, which increases confidence in the meaningfulness of the primary outcome.

Limitations of this study include the fact that about half of the participants already engaged in the recommended amount of aerobic exercise at the beginning of the study and about as many of the participants met the dietary recommendations at the beginning of the study. The health-conscious nature of this sample may be one reason why the benefits associated with exercise and consuming a healthy diet on cognition did not clearly manifest. Dietary intake was assessed using a one-time four-day food record, introducing the possibilities of under or over reporting, inaccurate recall, and non-representative samples. Physical activity was assessed using a questionnaire, in which the participants recorded aspects of their physical activity per month during the past 12 months, which introduces the same inaccuracies as those mentioned for the food records.

While at first glance this study seems to deliver disappointing results in regard to the efficacy of diet and exercise interventions, both the trend of the effect on cognition as well as the fact that the study participants had healthy lifestyles to begin with still add some credence to the usefulness of a healthy diet and adequate exercise for preventing cognitive decline. Thus, these results may help motivate people who want to minimize cognitive decline by exercising (at least aerobically) and adhering to a healthy diet.

This study showed that a combination of moderate intensity aerobic exercise in conjunction with a healthy diet may help prevent cognitive decline in middle and older adults without existing dementia. The effects of the interventions were very small, but this may be explained by the healthy baseline lifestyles of the participants.

Q. I have heard that there are specific foods that may help with cognition. Is that true and if so, what are those foods?

According to the National Institute of Health’s National Institute on Aging, to date there is no evidence that a specific food can prevent cognitive decline. However, a study found that, based on older adults’ reporting of their diet, eating a daily serving of leafy green vegetables like spinach and kale was associated with slower age-related cognitive decline. A systematic review of cohort studies showed that increased intake of vegetables is associated with a lower risk of dementia and slower rates of cognitive decline in older age. Studies have also shown that eating a diet that regularly includes fish is associated with slower age-based cognitive decline.

Q. Aren’t there other lifestyle factors besides diet and exercise that are important for preventing cognitive decline?

Yes. There is evidence to support the idea that keeping your mind active, maintaining social connections, managing high blood pressure and stress, and getting enough sleep may help prevent age-related cognitive decline, although the evidence is not currently strong. A systematic review and meta-analysis showed that lower educational attainment and decreased physical activities are strong predictors of Alzheimer’s disease.

Q. Are there any supplements that can help prevent age-related cognitive decline?

Studies^[17] have shown either mixed or negative results regarding the prevention of cognitive decline with the aid of various supplements. Some formulas focus on vitamin E, B vitamins, omega 3 fatty acids, or combinations of these. This is probably because there is good evidence to suggest that the Mediterranean, DASH, and MIND diets may improve cognitive function and these compounds are present in good amounts in these diets. However, it is not known whether it is the amount of the nutrients, combination of the nutrients, or even the nutrients themselves that are beneficial. Until more is known, it is probably best to stick with a healthy diet and exercise.

This study was designed to evaluate the effects of aerobic exercise, resistance exercise, and healthy diet alone and in combination on Finnish men and women ages 57–78. The only intervention that had even a trend toward improved cognition was the combination of aerobic exercise and diet. The overall healthy lifestyles of the participants included high volumes of physical activity and a surprisingly high adherence to Finnish nutrition recommendations, which may be a reason why the study did not find significant benefits. This does not, however, negate the putative benefits of corresponding exercise and diet-based lifestyle interventions. On the contrary, it should encourage everyone to make regular exercise and a healthy dietary pattern an integral part of their everyday lives.

There is currently no treatment that prevents or cures diseases associated with cognitive decline. However, some factors, such as exercise and certain dietary patterns, may help prevent cognitive decline. It is likely that a combination of healthy lifestyle behaviors, including eating healthy foods, exercising, keeping one’s mind active, maintaining social connections, managing high blood pressure, managing stress, and getting adequate sleep may reduce the risk of cognitive decline.