Short bursts of exercise can lower dementia risk

Just one or two sessions of physical activity at the weekend-;a pattern of exercise dubbed 'weekend warrior'---may be just as likely to lower the risk of cognitive decline, which can often precede dementia, as more frequent sessions, concludes research published online in the British Journal of Sports Medicine.

And it may be more convenient and achievable for busy people as well, suggest the researchers.

It's important to identify potentially modifiable risk factors for dementia because a 5-year delay in onset might halve its prevalence, they say, adding that nearly all the evidence to date comes from studies in high-income countries.

They therefore drew on two sets of survey data from the Mexico City Prospective Study, the first of which took place between 1998 and 2004, and the second of which took place between 2015 and 2019. 

Some 10,033 people (average age 51) completed both surveys and their responses were included in the analysis.

For the first survey, respondents were asked whether they exercised or played sports, and if so, how many times a week, and for how long (in minutes). 

Four groups were derived from the responses: the no exercisers; the 'weekend warriors' who exercised/played sports once or twice a week; the regularly active who did so three or more times a week; and a combined group comprising weekend warriors and the regularly active.

The Mini Mental State Exam (MMSE) was used to assess cognitive function at the time of the second survey. A score of 22 or less out of 30 was used to define MCI.

In all, 7945 respondents said they didn't exercise at all; 726 fulfilled the definition of a weekend warrior; 1362 said they exercised several times a week; and 2088 made up the combined group.

During an average monitoring period of 16 years, 2400 cases of MCI were identified. MCI prevalence was 26% among the no exercisers; 14% among the weekend warriors; and 18.5% among the regularly active. 

After taking account of potentially influential factors including age, educational attainment, smoking, nightly sleep, diet and alcohol intake, weekend warriors were 25% less likely to develop MCI than the no exercisers, while the regularly active were 11% less likely to do so. Those in the combined group were 16% less likely to do so.

When MCI was defined as an MMSE score of 23 or below, 2856 cases were identified. And MCI prevalence rose to 30% among the no exercisers, 20% among the weekend warriors, and 22% among the regularly active.

Compared with the no exercisers, weekend warriors were 13% less likely to develop MCI, while the regularly active and those in the combined group were 12% less likely to do so. The results were similar for both men and women.

The researchers estimated that, in theory, 13% of cases might be avoided if all middle aged adults exercised at least once or twice a week. 

This is an observational study, so no firm conclusions can be drawn about causal factors. And the researchers acknowledge various limitations to their findings. For example, the survey respondents might not have been truly representative of middle aged adults and there were no objective measures of physical activity.

But there are several possible explanations for the seemingly protective effect of exercise on brain health, they explain.

"For example, exercise may increase brain-derived neurotrophic factor concentrations [molecules that support the growth and survival of neurons] and brain plasticity. Physical activity is also associated with greater brain volume, greater executive function, and greater memory," they write.

"To the best of our knowledge, the present study is the first prospective cohort study to show that the weekend warrior physical activity pattern and the regularly active physical activity pattern are associated with similar reductions in the risk of mild dementia," they continue.

And they go on to suggest that the findings "have important implications for policy and practice because the weekend warrior physical activity pattern may be a more convenient option for busy people in Latin America and elsewhere."