Can your physical strength affect your chance of having depression? A study published in Evolution, Medicine, and Public Health suggests that it can; stronger grip strength is associated with lower rates of depression.
Depression is a very serious mental illness that can cause significant levels of distress and even lead to suicide. Women are twice as likely to suffer from depression as men are, but a previous study showed that grip strength mediated these prevalent sex differences.
In their new study, researcher Caroline B. Smith and colleagues sought to see if this finding would replicate, as the results were striking and surprising. Previous research has found that as grip strength is stronger, depression is lessened and that generally, men have stronger grip strength than women.
Smith and colleagues used data from the National Health and Nutrition Examination Survey, which included information from 8,576 participants. The PHQ-9 was utilized to measure depression, including suicidal ideation. Grip strength was measured on each hand three times, and the highest score on each hand was used.
Health, socioeconomic, and hormonal variables were measured and identified as potential confounds. Smith and colleagues created exact replications and partial replications. The partial replications employed some of the potential confound variables.
Results showed that in the exact replication, grip strength did mediate the gender difference in depression, but to a smaller degree than it did in the original study. For most of the models run in this study, this relationship was significant, suggesting that strength does have an independent effect on depression, even when other variables are controlled for. Strength had the biggest effect on depression when considering suicidality symptoms, low interest, feeling down, and feeling bad.
This study took the important step of replicating previous surprising and novel findings. One limitation is that this study is cross-sectional, meaning that no causal relationship can be extrapolated from this data. Another limitation is that grip strength may not be the best measurement for assessing physical formidability. Additionally, depression can be affected greatly by one’s environment, which this study could not control for.
“We argue it is important to consider physical factors such as formidability (e.g. body size, upper body strength) that might shape interactions with social partners and thus also shape risk of depression—especially symptoms like suicidality, low interest, feeling down and feeling bad,” the researchers concluded. “As this replication study has shown… physical formidability might protect against depression, and sexual dimorphism in upper body strength (proxied here with grip strength) may partially account for the sex difference in depression.”
The study, “Strength is negatively associated with depression and accounts for some of the sex difference: A replication and extension“, was authored by Caroline B. Smith, Tom Rosenström, and Edward H. Hagen.
