Exercise plus an active social and mental life was linked to about 7 more years free of memory problems

Two habits come up again and again in research on keeping the mind sharp with age: being physically active and staying mentally and socially busy. Most studies look at them one at a time. That leaves a practical question open: if someone doesn't exercise, can a full social life and plenty of hobbies make up for it?

A team including researchers at Shanghai Jiao Tong University School of Medicine tried to answer this using four long-running surveys of middle-aged and older adults on three continents. Their headline: people who were high in both habits had the lowest rate of new cognitive impairment (problems with memory and thinking) and the most years free of it, while being high in just one habit was linked to a smaller advantage.

What they did

The researchers combined data from the China Health and Retirement Longitudinal Study (CHARLS), the US Health and Retirement Study (HRS), the English Longitudinal Study of Ageing (ELSA) and the Korean Longitudinal Study of Ageing (KLoSA). These surveys return to the same people repeatedly.

• Who: people aged 50 or older without cognitive impairment at the start, with at least two survey rounds. That left 54,217 people for the main analysis.
• Exercise: structured exercise meant planned activity done on purpose for fitness, sport or health, not everyday movement. People answered questions about it themselves, and each survey's answers were sorted into "high" or "low".
• Engagement: cognitive–social engagement covered things like seeing friends, clubs, hobbies, volunteering, religious or cultural activities, games, classes and internet use, again sorted into high or low.
• Four groups: at each survey round, everyone was placed in one of four groups: low in both, high exercise only, high engagement only, or high in both. People could move between groups over time.
• Outcome: the first survey round at which a person was classed as cognitively impaired, based on that survey's thinking tests.
• Fair comparison: the analysis accounted for age, sex, education, marital status, smoking, alcohol, body weight and long-term illnesses such as diabetes and heart disease.

The team also used a multistate life table, a way of turning yearly rates of moving between "healthy", "impaired" and "dead" into the number of years a typical 50-year-old could expect to spend in each state.

What they found

• Lower rates of new impairment. Compared with people low in both, the hazard ratio (the relative rate of new cases) was 0.80 for high exercise only, 0.79 for high engagement only, and 0.70 for high in both.
• Not interchangeable. The two single-habit groups did not clearly differ from each other. But the group high in both had lower rates than either single-habit group.
• Healthy years. From age 50, expected years free of cognitive impairment were 17.5 for low in both, 20.1 for high engagement only, 23.2 for high exercise only and 24.7 for high in both: a gap of 7.2 years between the extremes.
• Longer lives overall. Total remaining life expectancy also differed widely, from 28.0 years in the low-in-both group to 39.1 years in the high-in-both group.
• Staying the course. Among 29,758 people with five rounds of data, those who stayed high in both had the lowest estimate of risk, though this result was not clear-cut statistically.

The main pattern held when the team ignored cases in the first one or two years, changed the cut-offs for "high" and "low", or left out one cohort at a time.

What to keep in mind

• The authors' own limits. Exercise and engagement were self-reported, and the surveys asked about them in different ways. Each survey defined cognitive impairment differently, so some people may have been misclassified. Income and wealth could not be accounted for. Other hidden differences between people, and the possibility that early, unnoticed decline made people less active (rather than the other way round), cannot be ruled out. Brain changes, fitness and other possible mechanisms were not measured.
• Model-based years. The authors stress that the extra healthy years are estimates from a model and associations, not a guaranteed result of changing habits.
• More years with impairment too. The high-in-both group lived longer overall, so it also had more years with cognitive impairment. The authors caution against reading the results as a squeezing of impairment into a shorter part of life.
• Results varied between countries. Especially for engagement, the strength of the links differed a lot between cohorts, perhaps because activities like volunteering or going online mean different things in different places.
• Links, not causes. Despite the authors' talk of "benefits", this is an observational study. It shows that the habits and better cognitive outcomes went together, not that the habits produced them.

Why it matters

Public health advice often treats exercise, social life and mental stimulation as separate messages. This study, drawing on tens of thousands of people in Asia, North America and Europe, suggests they may work best together: a busy social and mental life was linked to some advantage on its own, but did not appear to stand in fully for exercise. Whether combining both actually delays cognitive impairment is something only intervention trials, which the authors call for, can show.