Promoting healthy lifestyle behaviors is considered an effective strategy for preventing and/or treating diseases (1). The secular trend in healthy lifestyles throughout the 20th and 21st centuries shows that a growing number of people have become aware of the role of lifestyle changes in disease prevention. Maintaining healthy lifestyles, such as a healthy diet, a healthy body weight, and being physically active, has a large impact on morbidity and mortality. A study of the USA population shows that a healthy lifestyle can significantly lower premature mortality and prolong life expectancy (2). In a variety of countries, perhaps as a result of to research and social messaging, there are beneficial changes in lifestyle occurring at the population level. Even in their later years, older individuals show they are capable of learning new skills and participating in social and physical activities.

Governments and public health officials worldwide have promulgated and promoted guidance on healthy lifestyle factors in the pursuit of improving physical and mental health. It is well acknowledged that physical activity is crucial for maintaining independence, preventing disease, and enhancing the quality of life, particularly among older individuals. In order to embrace health benefits, such as a decreased risk of mortality, cardiovascular disease, depression, and dementia in older adults, guides such as the 24-h Movement Guidelines (3), which incorporate physical activity, sedentary behavior, and sleep, have been promoted in Canada. However, physical inactivity among older adults is still a significant risk factor for increasing the burden of disease, especially globally (4).

Also, older adult smokers are more likely than non-smokers to experience worse outcomes from major age-related disorders and have poorer management of those disorders (5). Smoking may also reduce the effectiveness of vaccines and raise the risk of many cancers in the elderly population (6). Depressed people have been found to be more likely to smoke, which may be due to nicotine’s powerful neurophysiologic effect (7, 8). A Canadian longitudinal study using national survey data showed that prior smoking was a significant risk factor for incident depression (9). Additionally, there is a great deal of evidence demonstrating complex behavioral and neurophysiologic interactions between smoking and mental health (10). Research supporting a causal relationship between smoking and depression shows a reduction in depression among those who quit smoking (11). Even in later years, quitting smoking can considerably lower mortality and enhance the quality of life, particularly in older people with underlying conditions associated with smoking, e.g., COPD (12). However, an analysis of a repeated multi-wave cross-sectional household survey in England, found that despite being less dependent on nicotine than younger smokers, older smokers appeared less motivated to quit smoking and were less likely to be offered support to quit smoking (13).

According to an analysis of the National Health Interview Surveys (USA) from 1997 to 2014, the number of Americans aged 60 and older who drink has steadily increased, especially among women (14). Some special considerations facing older adults who drink alcohol include a higher sensitivity to alcohol, increased health problems, and harmful interactions with medications. As people age, their bodies process alcohol more slowly, making them more vulnerable to the negative effects of alcohol. Families, friends, and healthcare professionals may fail to take elderly people’s drinking into account. This may be the case because older persons’ drinking-related side effects are sometimes misinterpreted as aging-related problems, such as balance issues.

Depression, one of the most prevalent mental illnesses in older adults, affects approximately 7% of the senior population worldwide (15). By 2020, depression has become the second leading cause of death and is thought to have a secondary role in 50–70% of suicides among the elderly (16). Healthy lifestyles have been identified to contribute to a lower risk of chronic diseases and mental disorders, especially depression (17–19). Even though the majority of cases of depression cannot be prevented, healthy lifestyle changes can have benefits for older individuals’ mental health in the long run. Previous studies have demonstrated that leading a healthy lifestyle, which includes regular exercise, physical examinations, and following dietary rules, can reduce the risk of depression in older people (20). It has been shown in many populations that those who do not live a healthy lifestyle are more prone to experiencing depression (21–23). For instance, there is strong evidence for an inverse association between physical exercise and depression in the general population (24) and older individuals (25). Physical activity has been identified as a favorable non-pharmaceutical strategy for treating and preventing depressive symptoms in older adults (26). Bidirectional associations between tobacco use, heavy drinking, and depression among older adults have been widely observed (27). Findings from prospective, longitudinal studies have validated that smoking and alcohol drinking have a long-term impact on later depression and vice versa (28, 29).

Evidence shows that individual behaviors and mental health have increasingly changed at the population level (30). People born in certain birth cohorts come of age at specific periods of history and experience disparate socio-economic and political environments. As the imminent sociologist C Wright Mills (31) wrote, “Neither the life of an individual nor the history of a society can be understood with understanding both.” Each birth cohort lives and ages within a historical capsule. These unique economic characteristics, political conditions, and social norms vary from time to time in different countries. They become essential exposures in the development of lifestyle behaviors and psychological outcomes. Identifying population-level factors influencing unhealthy lifestyles and psychological consequences have significant public health implications.

How do the associations between unhealthy lifestyle factors and depression vary across and among individuals born in different periods as they age? We examine those questions among Canadians aged 65+ born between the 1910s and 1950s. It is an unexplored topic. This study aims to provide a comprehensive picture of how unhealthy lifestyle factors, the prevalence of depression, and their associations change among Canadians 65+ across the eight birth cohorts born between 1910 and 1949, thus having been exposed to diverse epoch experiences as they have aged.

This study compared the relationship between health risk behaviors and depression among Canadians 65+ born at various times through the first part of the 20th century. By comparing these birth cohorts, we can seek the effects arising from the historical experience of various birth cohorts. Canadian 65+ born in more recent cohorts, in the 1940s, are more physically active but smoke and drink more than those born earlier in the century. The prevalence of depression increased in all health risk behavior groups from earlier to more recently born cohorts, specifically for current smokers and inactive people. We also found that inactivity/smoking-attributable depression showed an increasing linear trend from earlier to recent birth cohorts. Regular drinking was negatively associated with depression, except for those born in the 1940s. To our knowledge, the current study is the first to examine the broad link between health risk behaviors and depression among older adults across birth cohorts in large samples of the general population.

More and more older Canadians are adopting healthy lifestyles in the late 20th and early 21st centuries (39–41). In the current study, the overall drop in physical inactivity and cigarette consumption from 1994 to 2014 seemed likely to be associated with the strikingly greater public awareness of the health hazards of physical inactivity and smoking. A wealth of continuing public health warnings, education, and specific prohibitions on unhealthy lifestyles have been strongly supported by national and provincial governments. From the cohort analysis, it can still be observed that seniors born in the more recent cohort are more likely to smoke and be regular drinkers of alcohol. A diversity of studies has recognized the inverse relationship between smoking and age among older adults (42, 43). As the country’s population ages and we transition from birth cohorts with more permissive smoking norms to those with more restrictive norms, we expect that fewer seniors will be smoking cigarettes, but the role of smoking in depression will increase. However, currently, a greater proportion of Canadian seniors born in the 1940s continue to smoke cigarettes in spite of mounting societal pressure not to do so. There has been a substantial increase in the number of seniors who are now former smokers across birth cohorts; this is especially true for those seniors born in more recent cohorts. While quitting smoking is still advantageous for older people, prevention and early intervention are unquestionably more advantageous. Obviously, measures to improve wellbeing in older adults’ life should be implemented as early as possible. The results of this study indicate that alcohol consumption is still a major public health issue in Canada. As we can see, seniors born in the more recent birth cohorts consume alcohol more often than those born earlier in the 20th century. From a prevention perspective, more attention needs to be paid to Canada’s Low-Risk Alcohol Drinking Guidelines for Older Adults and the recommended alcohol consumption limits (44).

Of key public health interest is how social norms shape older individuals’ physical and mental health. Both cohort-specific norms and individuals’ attitudes or beliefs affect behavior factors and impact both physical and mental health. The “birth cohort effect” in our analysis reflects how these social, economic, and political resources to which people are exposed as they progress through their life journey significantly influence their health. They become essential exposures in the development of lifestyle behaviors and psychological outcomes. The more recently born seniors have a clinically higher risk for depression, leading to increased depression rates across all behavioral groups.

People born in more recent cohorts share the highest risk for inactivity-attributed risk for depression; this is especially true for seniors born in the 1930s. In Canada, people born in the 1930s are the parents of baby boomers (those born after World War II). They had larger-sized families, which contributed to the baby boom in Canada. They also experienced the Depression in the 1930s and World War II (1941–1945) in youth and as young adults. The antidepressant effects of exercise have been confirmed by extensive research (45–47). The benefits of physical activity may be more important for seniors because of the high risks of functional disability and physical and mental illnesses.

Our analysis of the change across survey years showed that cigarette smoking was consistently and progressively associated with depression among seniors from 1994 to 2014. Over time, as cigarette smoking became less prevalent among older adults, a stronger association with depression became evident. Such a model is consistent with the epidemiologic literature on tobacco consumption (48, 49). A historical trend analysis concluded that when cigarette consumption declined, its positive relationship with depression became more robust at the population level (50). The cohort results in this study also show that the relationship between smoking and depression increased among seniors from those born in the early 20th century to more recent birth cohorts born mid-century. The corresponding link between tobacco use and psychopathology has also been documented by a study on the trends of psychopathology among cocaine abusers (51). Some psychosocial and genetic factors can explain the increasing comorbidity with tobacco use and depression across birth cohorts. Research shows that members of more recent-born cohorts are prone to deviant behaviors and have more genetic liabilities to addiction than earlier-born cohorts (30, 52–54). It is also possible that the cigarette smoking-depression link is underestimated because of the possibility of the differential mortality effects of cigarette smoking. More specifically, older smokers with depression have higher mortality in earlier-birth cohorts than those in more recent-born cohorts. A prospective cohort study could be used to address the issue.

Previous studies on the link between light-to-moderate alcohol intake and psychological consequences in adults have produced inconsistent results. For example, a literature review suggested that moderate doses of alcohol might be beneficial to psychological wellbeing (55). Some studies might explain this as alcohol drinking resulting in stress-reduction effects that lower mental illness susceptibility. In contrast, García-Esquinas et al. (56) found no consistent protective effects of light to moderate alcohol consumption on depression in older adults. Future research should examine whether and how changes in alcohol consumption patterns affect depression risk by using repeated measures of alcohol intake and taking into account cultural norms regarding alcohol use and changes in those norms.

Cohort analysis reflects the unique social, economic, and political environments of generations born in different time periods but of the same chronological age. The period analysis reflects the general social environment of all individuals living at a specific time in history (57). Our study explored the changes in associations between health risk behaviors and depression among Canadian seniors born in different birth cohorts from the early to the mid-20th century. Our study is based on extremely large and representative Canadian seniors’ population samples. These findings can be generalized and help inform public health planning and interventions in Canada.

The prevalence of depression increased among Canadian seniors from the earlier- to recent-born cohorts. The contribution of physical inactivity and cigarette smoking to depression prevalence is a greater risk for Canadian seniors born in more recently born cohorts as opposed to those born earlier in the 20th century. Smoking has become more firmly established as a risk factor for depression in the more recent birth cohorts. In contrast, moderate alcohol use was associated with a decreased risk of depression in earlier birth cohorts, but the strength of that connection has diminished, becoming non-existent in the most recent birth cohort. Identifying changing relationships between health risk behaviors and depression is meaningful for developing public health strategies and allocating health resources for older Canadians.

The original contributions presented in this study are included in the article/Supplementary material, further inquiries can be directed to the corresponding author.

In accordance with local legislation and institutional requirements ethical review and approval was not required for this study. The patients/participants provided their written informed consent to participate in the original sources surveys from which this study’s data is derived.

Both authors contributed to the design of the study, contributed to further revisions of the manuscript, and approved the final submitted version of the manuscript. GY was responsible for the acquisition and analyses of the data and prepared the first draft of the manuscript. CD’A critically reviewed the initial draft of the manuscript.