Physical activity tends to decrease with age [34, 35] while sitting time tends to increase , and the association between ageing and chronic disease has been well established at the population level [37, 38]. Our findings show that, even when age was held constant, higher volumes of sitting were associated with increased odds of diabetes and overall chronic disease.
We controlled for several factors that could potentially confound the associations examined in this analysis – one of the more influential factors being functional limitation. Advancements in medical care and technology have resulted in improved treatment and earlier diagnosis of conditions, leading to a potential reduction in disease-related functional limitation [39, 40]. The presence of chronic disease, however, often brings with it some decline in functional limitation [41, 42]. Individuals who experience higher degrees of limitation may be less likely to participate in physical activity, and may consequently spend more time in sedentary behaviours such as sitting. Adding functional limitation in the final model allowed us to explore the unique contribution of this potentially confounding variable, while still controlling for additional covariates.
After partially adjusting for covariates including age and BMI, the associations between sitting time and most chronic disease variables included in this analysis were attenuated, with the exception of overall chronic disease and diabetes, where the associations were strengthened. After adjusting for all covariates including functional limitation, these associations were consistently attenuated, although higher quantities of sitting time were associated with significantly greater odds of having diabetes. These findings support those from a prospective cohort study by Hu et al.,  who found that sedentary behaviour was directly associated with diabetes risk, although this earlier study focused primarily on television viewing as a marker of sedentary behaviour. Additionally, males in all sitting time categories above the reference category were significantly more likely to report ever having a chronic disease (overall chronic disease).
In response to the relatively limited body of evidence surrounding the health of Australian males, the National Male Health Policy specifically outlined a priority area for building a strong evidence base on male health . The findings of this study contribute to this body of evidence by highlighting the importance of considering both physical activity and sitting time as independent factors associated with diabetes in a sample of middle-aged Australian males. Our findings suggest that sitting time is significantly associated with diabetes and overall chronic disease, independent of physical activity; building upon existing literature in which physical activity and aspects of sedentary time have been previously established as independent risk factors for CVD, metabolic syndrome, and all-cause mortality [15–18].
When interpreting the findings of this study, potential limitations must be considered. Being cross-sectional in nature, we cannot establish whether the volume of sitting time led to the development of these chronic diseases, or whether the presence of these chronic diseases influenced participants’ sitting time. Evidence from previous epidemiological studies, however, suggests that higher volumes of sitting time can present risk for diabetes [12, 43]. Additional research in this particular population group is required to establish temporal sequence and further examine the potential dose–response relationships identified between sitting time and chronic diseases in the male population. Second, the self-report nature of measures used in the 45 and Up Study baseline questionnaire must be considered when interpreting the findings. Although self-report data can be affected by recall bias, or under- or over-reporting , self-report methods are often used in large-scale studies such as the 45 and Up Study due to the associated feasibility, cost-effectiveness, and ability to collect data from large groups of people .
The potential for misclassification of the variables used in this analysis must be acknowledged. It is possible that some participants may have incorrectly reported (or failed to report) having a chronic disease, while others may have under- or over-reported their daily sitting time. While these potential misclassifications may have impacted upon the strength of the observed associations, even after adjusting for a range of covariates, sitting time was still strongly and significantly associated with diabetes. In addition, while other studies on the association between sedentary time and health outcomes have adjusted for potential confounders including light intensity activity or overall energy expenditure [46, 47], only data on overall time spent in physical activity in the previous week were included in this study. It is also possible that a proportion of the moderate intensity activity reported in the 45 and Up Study baseline questionnaire was actually light intensity, which may have led to an overestimation of moderate intensity physical activity. The third potential limitation is that the sitting time variables did not delineate specific domains of sitting time, such as office work, driving, other passive travel, and sitting during leisure time.
Given the potential for selection bias, as well as the 18% response rate pertaining to the 45 and Up Study and the fact that we further excluded males for whom certain data were not available, the potential impact upon the external validity of these findings should be considered. Although the characteristics of the 63,048 males included in this analysis may not be truly representative of the NSW middle-aged male population, sitting time, within this large sample of males, was strongly and significantly associated with diabetes, and to a lesser extent, overall chronic disease. Furthermore, the 45 and Up Study is the largest study of healthy ageing to be carried out in the Southern Hemisphere, and is likely to be one of the more representative large-scale cohort studies conducted globally .
There are also several other noteworthy strengths of this study, including the large sample size and the broad range of health-related variables on which data were collected. A total of 63,048 males from the 45 and Up Study baseline dataset were included in the analysis for the current study. Being that middle-aged males are a relatively understudied population group, the findings of his study will help to partially fill a current gap in the literature concerned with male health. This study is among the first to examine the associations between a range of chronic diseases and sitting time in middle-aged Australian males, while statistically controlling for likely confounders. The 45 and Up Study will collect much-needed longitudinal data on middle-aged and older Australian adults over the coming years, allowing researchers to monitor and investigate trends observed in this initial baseline data.