This extensive community-based, prospective cohort study showed that more frequency of playing cards/mahjong was associated with a significant reduction in the risk of dementia among older adults individuals aged 65 and older. Furthermore, we found that the protective association was stronger for older adults who reported playing cards/mahjong almost every day with regular exercise than those without regular exercise. We did not find any significant difference in age, sex, and MMSE score median, and that further sensitivity analysis yielded no substantial changes in our findings after adjusting confounding factors.
The present findings align with several previous studies that active participation in stimulating intellectual activities (such as playing cards or checkers), especially among the older adults, is associated with better cognitive functioning [6, 21]. In addition, some studies had also found that more frequently playing stimulating intellectual games (such as cards, bingo, chess, mahjong, crossword puzzle) were associated with a decreased risk of dementia [22–24]. The reasons why these stimulating intellectual games can reduce the risk of dementia may be explained by the fact that playing cards or mahjong (game activities welcomed by Chinese circle) is a strong and comprehensive stimulating activity in cognitive domains (involving attention, reasoning, memory, and initiative capacity) 24 and interpersonal social communication, which is also proved to be help to reduce the risk of dementia or cognitive impairment [25, 26]. However, as we know, many previous studies did not fully consider other confounding factors (such as education level and whether live with family members) and baseline cognitive status, both of which can lead to potentially biased results. Moreover, our finding was consistent with a recent prospective study result that active participation in playing cards/mahjong might be in favor of decreasing the risk of dementia in older adults . However, the study was followed-up for only three years, and relevant evidence showed that dementia was considered to develop slowly over many years , so the causality of this study conclusion was still controversial. Additionally, most studies had incorporated various types of stimulating intellectual activities as independent variables, while our study included playing cards/mahjong as the only factor to explore the independent impact on the risk of dementia in the older adults through adjusted as many confounding factors as possible.
A few prospective studies also had investigated the relationship of other types of leisure activities (such as social, recreational, physical) to cognitive decline or dementia, and their results did not identify that frequency of participation in social or recreational or physical activities was associated with lower risk of cognitive decline or dementia [6, 14, 28]. These results were contrary to the relationship between stimulating intellectual activities and cognitive decline or dementia, but these findings were significant because they showed that the association of cognitive decline or dementia risk reflected mental stimulation rather than nonspecific results of other types of leisure activities. Compared with stimulating intellectual activities, these activities are usually more passive and have less cognitive involvement, so we deduce that stimulating intellectual activities might be more effective than engaging in various nonintellectual leisure activities (such as recreational, social, and physical) in preventing dementia.
The potential mechanisms involved for the association of stimulating intellectual activities with incident dementia are no consensus. One hypothesis is that frequent participation in cognitively stimulating activities can protect the cognitive function of the older adults from decline , because repeating some cognitive skills can make neurons more active and less vulnerable to disruption by dementia pathology . Another similar view points out that frequent cognitive stimulating activity may strengthen thought processing skills, such as ratiocination, calculation, and perceptual speed, which may be conducive to compensate and resist for age-related decline in other cognitive systems . Some studies had explored possible biological mechanisms for the association of cognitively stimulating activities with cognitive function [32, 33]. These findings manifested that being mentally active may delay the onset of clinical dementia by improving cognitive reserve. According to cognitive reserve theory in neuroscience, people with a higher level of the cognitive reserve can more buffer the effects of neuropathology in brain anatomical substrate and function, and also have greater dynamic neural network compensation such that the larger cognitive reserve, the more serious the pathological damage needed to cause functional impairment [33, 34]. A recent study showed that cognitive stimulating can improve functional connectivity between the hippocampus and superior frontal cortex to resist cognitive function decline . The above findings show that cognitive training may improve cognition, possibly through different neural regulation mechanisms, which can explain our findings that more frequency of playing mahjong/cards lowers the risk of dementia.
Regarding the strengths of this study, it is a community-based, national-wide prospective design, the large sample of the over 65 older adults, a relatively long follow-up period with about three years evenly spaced observations per individual, adjustment for established and potential confounders. Of course, our study also has some limitations. First, our findings only apply to the older adults in China. Due to the cognitive function effects of playing cards/mahjong may be different between young and older adults individuals, this effect should be carefully extended to young people. Second, information on covariates and dementia status is collected through self-reported in the form of a questionnaire; thus, recall bias and information bias are possible. Third, we do not control other types of leisure activities. Although this is also important, it does not alter the main results in that frequent playing cards/mahjong is associated with a significantly decreased risk of dementia.
In conclusion, our study provides evidence that frequently playing cards/mahjong may decrease the risk of dementia among Chinese older adults over 65 years old. Given China's huge population base and increasing aging, promoting more frequent participation in this activity could protect against the onset of dementia, and also solve problems in aging societies.