This is the first study to our knowledge to investigate a MAI incorporating reading, playing mahjong or cards and computer use in relation to all-cause mortality. We found that multiple mental activities among older Chinese adults were associated with a decreased risk for all-cause mortality over 4 y of follow-up. There was a clear association between the number of mental activities, as indicated by MAI score, and all-cause mortality.
Previous evidence is accumulating on the cognitive health of the mental activities. Li and colleagues indicated that reading and computer use were associated with lower risk of mild cognitive impairment in a population-based study34. Lindstrom et al. found an inverse relationship between intellectual activities (reading, playing cards, playing a musical instrument, and letter writing) and Alzheimer’s disease or other forms of dementia in a US-based population17. Verghese et al reported that cognitive activities (reading, writing, doing crossword puzzles, playing board games or cards, and playing musical instruments) were associated with a reduced risk of dementia14. Despite the heterogeneous measures, risk classification, sample characteristics, and follow-up time of these studies, the association between mental activities and cognitive health has been consistent, suggesting the generalizability of these findings. Such beneficial role of mental activities is furthered here by implicating its protective role against all-cause mortality in older people in our study. Cognitive impairment has a significant impact on mortality and disability of order population35. According to data from the Centers for Disease Control and Prevention (CDC), 121,404 people died from Alzheimer’s disease in 2017 and the rate of death from Alzheimer’s disease dramatically with age, especially after age 6518. Therefore, a potential mechanism by which mental activities influence mortality is through protecting the cognitive impairment, at least in part.
It is worthy to note that, among the three dichotomized individual mental activities, playing mahjong or cards showed independent association with all-cause mortality. One explanation is that playing mahjong or cards incorporates social engagement. Social engagement, defined as the maintenance of many social connections and a high level of participation in social activities, has been indicated to prevent cognitive decline in older persons36–38. Additionally, social activities predominantly affect the immune system and influence inflammatory processes in the brain 39, 40. All these results support our findings that playing mahjong or cards has an independent protective role in all-cased mortality.
Stratified analysis showed a significant relation between mental activity and all-cause mortality among participants with physical inactivity in late life, indicating the supplemented role of mental activity in healthy living, especially for the older people who is unable to perform effective physical activity due to severe chronic disease. Physical activity is a pivotal lifestyle behavior. Regular physical activity has been irrefutably identified as protective factor for all-cause mortality41–43, and the benefit of physical activity was independent of the type of physical activity 44. Here our study showed the consistent effect of mental activity with PA on all-cause mortality in older population. In addition, some studies have indicated that the cognitive function and physical function influenced each other in a feedback loop.45, 46. A protective effect of physical activity against cognitive impairment has been reported in many studies47–50 and the benefits of physical activity on cognitive function can be attributed to an ameliorated overall health condition51. Conversely, mental activity has been reported to be associated with enhanced memory, executive function, language, and cognitive skill52, which may influence the practice of regular physical activity. For example, the execution functions, including of volition, planning, purposive action, performance monitoring and inhibition53, may enable people to consistently engage in physical activity in older to achieve long-term health benefits54.
We also found that MAI score was associated with lower all-cause mortality in participants without cancer, but not in cancer patients. In fact, many studies showed the beneficial effect of mental activity or social activity on the quality of life which was reported to decreased the risk of breast cancer mortality and recurrence55, enhanced the colorectal cancer overall survival56, and influenced the cancer patient outcomes, including physical burden, psychosocial burden, and financial burden57. Hence, we believe that whether from improving the mental health of cancer patients or improving the survival rate of non-cancer patients, mental activity should be concerned in older people health. In addition, we also found the potential protective role of MAI in all-cause mortality among participants who were diagnosed with cardiovascular or metabolic disease (HR = 0.67, P = 0.025 in univariate analysis, HR = 0.70, P = 0.067 in multivariate analysis, Fig. 3). Accumulating evidence have indicated that leisure activity, including watching TV20, internet use21 and reading22, 23, can make a significant contribution to overall life satisfaction and psychological well-being24, 25, which in turn is associated with lower risk of cardiovascular disease58, 59. Thus, a potential pathway by which mental activity influence all-cause mortality may be through reducing the risk of cardiovascular disease or reducing the effect of cardiovascular disease on mortality.
Limitations in the current study should be acknowledged. Firstly, it is important to acknowledge that not all three mental activities contribute to mortality similarly and that their combined effects may not be additive. However, because of the short follow-up period and small sample size, we didn’t get the enough prevalence of specific combination pattern of mental activities to analysis their associations with all-cause mortality (e.g., prevalence of combination of reading and computer use, combination of playing mahjong or cards and computer use, and combination of both three mental activities were 1.0% (n = 41), 0.2% (n = 9) and 0.4% (n = 14), respectively). Secondly, time spent in each activity was not measured, this may modify the effect of mental activity on mortality. Thirdly, the effect of mental activity on mortality was not adjusted for cognition status because there was an absence of measure of cognition at baseline. Baseline participation in mental activities may have been influenced by cognition and future studies incorporating the cognitive data are needed to illustrate the modifying effect of cognition status on mortality caused by mental activity. Fourthly, this study could be further strengthened by including cause-specific mortality outcomes, but these data are not yet available for the time period studied. Finally, this study was composed of older Chinese adults living in a large city, Shanghai, thus potentially limiting the generalizability of our results.