The study found that physical activity had a suppressive effect on the risk of depression in the married group. After further controlling for demographics and some cognitive indicators, exercise remained a suppressive effect on the risk of depression among married women, but the relationship between exercise and risk of depression among married men was no longer statistically significant.
There is now much evidence on the physiological mechanisms underlying depression inhibition by physical exercise. In animal studies, physical exercise has been shown to promote elevated levels of antioxidant enzymes, brain-derived neurotransmitters, etc., and to reduce cortisol levels with reduced inflammation in brain tissue [19]. Neurobiology has shown that exercise increases the volume of grey matter in the brain, improves the microstructure of white matter, and is associated with functional connectivity in brain regions associated with major depression [20]. In addition to this, the social benefits of physical activity can also intervene in depression levels. For example, physical activity exerts a depression-inhibiting effect by strengthening an individual's self-concept and enhancing the level of perceived social support [21]. However, evidence from numerous studies suggests that there are differences in depression levels between the sexes, and gender-specific research on the effects of physical activity on depression levels remains relatively thin. In the present study, the gender differences in depression risk were the same as in other national studies, with women having higher rates of depressive illness than men [22–24], and the reasons for this can be explored in three main ways based on previous studies. First, there are physiological causes. For example, women have lower levels of 5-hydroxytryptamine, a pleasure-producing neurotransmitter [25], or reproductive depression caused by hormonal changes such as the menstrual cycle, pregnancy, and menopause. Secondly, social factors. For example, women in gender roles have higher stress levels and feelings of helplessness [26] and are also more likely to fall into contemplative patterns of repressed emotions. Third, reasons such as gender role characteristics make men more likely to be overlooked when self-reporting or diagnosing [27]. After controlling for relevant indicators, the defensive effect of physical activity on the risk of depression in women remained significant, but the intervention effect on the risk of depression in men was not statistically significant. Combining the above differences between the sexes, the analysis has the following reasons.
First, the biological mechanisms produced by physical exercise are more prominent for the female population. In an experiment on rats with vascular dementia, treadmill exercise, whether voluntary or mandatory, was found to upregulate their dopamine and 5-hydroxytryptamine levels to protect cognition [28], which has a compensatory mechanism for the lower turnover of 5-hydroxytryptamine levels in females [29]. In addition to this, under the same workload, women have more active sympathetic nerve activity and significantly higher levels of norepinephrine, epinephrine, and glucose than men, while at rest there is no difference in the indicators between the two [30]. Therefore, physical exercise is more effective in modulating some physiological levels in the female group than in the male.
Secondly, men in the marriage structure face social pressures that are different from those of women. The traditional marriage script requires men to take on the role of 'breadwinner', and in doing so, men gain decision-making power in the family while also bearing the corresponding family pressures. For example, gender roles have a moderating effect on anxiety in unemployed women when unemployment affects people's psychological well-being by depriving them of advantages such as the experience of social contact outside the home and the potential benefits of personal status [31], but can exacerbate negative feelings in the group of unemployed men [32]. In marital relationships, the female sample reported higher levels of relationship stress related to self, while the male sample reported higher levels of external stress, including transportation problems, job stress, relationship with leaders, and environment [33]. Therefore, objective stresses from external sources are difficult to intervene directly in their emotional state through physical exercise and are shown to regulate depression levels through perceived factors such as enhanced well-being and improved interpersonal relationships.
Again, differences in motivations and expectations of physical activity between the sexes lead to different intervention effects on depression. In a gender-specific survey, women's motivations for physical activity mostly focused on direct physical benefits such as appearance, health improvement, and weight control, whereas men wanted the hidden benefits of social interaction, social recognition, enjoyment, and strength through physical activity [34]. Women's expectations of physical activity are easier to obtain and quantify than men's, and a good exercise experience has a more direct effect on negative emotions, whereas men's exercise expectations require a longer perception process and are vaguely measured, making it difficult to obtain a definitive emotional experience, resulting in a less significant effect of physical activity on depression in men.
Finally, the lower self-reported rate of high depression risk among married men led to a less than significant impact of physical activity. The marital relationship is one of the most important factors influencing the psychological state of couples. In most national samples, married groups feel happier than unmarried groups, and being in a marriage is a favorable indicator of men's well-being, but not in female samples [35]. Upon entering marriage, both partners receive care and support from their spouses, and women provide far more care and support than they receive [36]. Data from a survey in rural China showed that levels of depression, aggression, low self-esteem, and suicidal ideation were higher among unmarried men and worsened with age, compared to married men who remained stable [37]. However, the tendency of men to be reluctant to disclose emotional problems to the outside world versus resolving them on their own, influenced by gender roles [38], also affects the veracity of their self-reports. This somewhat narrows the sample of men at high risk of depression and, in turn, is less typical in their responses to some indicators.