To the best of our knowledge, this is the first prospective study to clarify the combined effects of CHD and sarcopenia on new-onset depressive symptoms. In addition, after adjusting for potential confounders, CHD and sarcopenia were found to be independent risk factors of new-onset depressive symptoms. Co-occurring CHD and sarcopenia presented the highest risk of incidence of depressive symptoms in the study population.
In our study, the association between sarcopenia and depression has been discussed deeply in our previous studies . The most compelling finding was that sarcopenia combined with CHD had a further additive predictive value in discriminating older adults at high risk of new-onset depressive symptoms. Previous studies have reported that sarcopenia is closely related to a higher prevalence of established CHD. The presence of sarcopenia is also a contributing factor in poor cardiopulmonary function in patients with CHD [13,14,15]. Kim et al.  believe that the existence of sarcopenia increases the morbidity and mortality of cardiovascular diseases in the elderly. In patients with sarcopenia, the endocrine function of muscle cells is weakened, and muscle cells exert their endocrine functions by secreting cytokines that are beneficial to the cardiovascular system. Both a decrease in the amount of muscle cells and a decline in their endocrine function in patients with sarcopenia could have contributed to the poor clinical outcomes . Behavioural, genetic and inflammatory mechanisms, as well as changes in hormone levels, decreased physical activity, insulin resistance that could explain the presence of sarcopenia and coronary heart disease are linked to depressive symptoms. On the other hand, polyunsaturated omega-3 free fatty acid deficiency, hypothalamic-pituitary-adrenal axis and autonomic mechanisms are also possible link pathways .
Another possible underlying mechanism to explain our results is that sarcopenia and CHD form a vicious cycle. Previous research suggested that low muscle mass and muscle strength are associated with risk of atherosclerosis and endothelial dysfunction in the elderly [13, 27], which may worsen the progression of CHD. Our additional results demonstrated that poor physical performance (gait speed <0.8 m/s was associated with new onset of CHD (adjusted OR = 2.08, 95%CI = 1.08–4.00). At the same time, CHD can lead to a decrease in gait speed, reducing people’s willingness to attempt tasks that they are otherwise capable of performing . Subsequently, this decrease in physical performance and increase in restriction might lead to decline of muscle mass or strength, eventually leading to sarcopenia. Based on these previously discussed studies and our current findings, sarcopenia and CHD in older adults appears to have an interaction effect on new-onset depressive symptoms. However, the specific mechanism is still unclear and needs to be confirmed further studies involving larger populations and with longer follow-up durations.
Major differences in body composition, risk of CHD and risk of depression are known to exist between the sexes. In this study, however, we did not explore stratification by gender because of our small sample size. If stratified by gender, co-occurring groups were associated with depressive symptoms incidence from baseline to 1-year follow up in both men and women (men: OR = 18.58, 95% CI = 2.26–152.65; women: OR = 8.51, 95% CI = 2.61–27.74). The man group had a larger confidence interval because there were fewer people in the co-occurring group (n = 5), which would limit the reliability of the statistical analysis. However, we can find that the results are statistically significant for both men and women, and the deficiency is that the sample size is small. Therefore, in our statistical model, the final results were adjusted for gender and not stratified by sex in the study. This is consistent with several previous studies, which explored the sarcopenia with depression or CHD without grouping studies by gender . In the future, we need to further expand the sample size to explore whether there are gender differences between sarcopenia, CHD and depression.
This study suggests that older adults with CHD and sarcopenia should be identified early and targeted, so that further mental deterioration and other adverse health outcomes can be prevented. In particular, the American Heart Association (AHA) showed that depression was a risk factor for adverse medical outcomes in patients with CHD . Through this research, we have found the need to focus on physical function. In addition to exercise and nutrition to improve physical function and relieve depression, recent study shows that new drugs can significantly improve depressive symptoms in patients with heart disease . Therefore, much greater attention must be paid to mental health during cardiac rehabilitation and multifaceted interventions require to be considered.
Strengths and limitations
The strength of this study is that it is the first study to report that CHD with sarcopenia is a stronger risk factor for incidence of depressive symptoms. Moreover, findings may provide new insights for cardiac rehabilitation in older adults. Despite extensive efforts to curb study limitations, some limitations did still exist. First, the present study didn’t describe the severity of CHD or its treatment in sarcopenia patients with CHD. In addition, our participants were relatively healthy, we didn’t include participants who were unable to participate in the free annual national physical examination (eg, those bedridden or with serious disease). Given these reasons, the population studied may not be comprehensive enough. As a result, we may have underestimated the prevalence of sarcopenia, CHD or depressive symptoms. Thirdly, sarcopenia is a major risk factor for frailty, and frailty also has links with depressive symptoms and CHD. We need to acknowledge that the failure to assess frailty is a limitation of this study and we may pay more attention to the older adults with frailty in the future. Fourthly, this study sample was enrolled from a free physical examination program, and the sample size is small, rather than a representative sample. Sarcopenic obesity may act together to increase their effect on metabolic disorders, cardiovascular and mortality , while the small number of sample limited our research on sarcopenic obesity. Furthermore, the sample sizes limited our exploration of gender stratification. In the future, when our sample size expands, we will further stratify by gender to explore the correlation between sarcopenic obesity, CHD and depression. Lastly, the follow-up period was short. In future research, we plan to enlarge sample sizes and extend the time for follow-up, to increase the ability to evaluate relationships.