There are much research on the association between negative life events or physical activity with depression symptom, however, little was known about the correlation among the three elements. In the present study, we explore the moderating role of physical activity on the association between negative life events and depression symptom in newlyweds based on a large sample, multicenter cross-sectional study. The results showed that negative life events and physical activity were independently associated with depression symptom. Besides, the subgroup analysis showed that, compared to the women who experienced negative life evens and reported a low physical activity level (reference group), women who experienced negative life events and reported moderate or high physical activity had 37% and 27% lower odds of depression symptom, the women who had not experienced negative life events and reported low, moderate and high physical activity levels had 63%, 74% and 78% lower odds of depression symptom, respectively. Similar results were observed in newly married men. To our knowledge, this is the first study to investigate the moderating role of physical activity in the association of negative life events and depression symptom.
In our study, up to 27.4% of newlyweds women and 19.0% of newlyweds men met the criteria for depression symptom. In contrast, in two national surveys of American, the prevalence of major depression and minor depression among non-pregnant women were 4.8–7.0% and 4.3–11.4%, respectively [2, 26]. Besides, another study included 512712 adults in China found that 17.96% of the people was diagnosed with clinically significant depressive symptoms [27]. The possible explanations for our increased prevalence might be attributed to the coronavirus (COVID-19) pandemic [28] and used different scale and cut-off value to screen depression symptom. The incidence of estimate for negative life events was 71.4%, which was slightly lower than proportions reported in a representative sample of adults in American (72.8%) [29], but much higher than that of a large cross-section study conducted during 2004 and 2008 in China (71.4% vs 8.5%) [11].
Our findings demonstrate that negative life events was associated with a higher risk of depression symptom for both newly married man and women during the no-pregnant period, which is consistent with that of different countries and population. For example, several systematic reviews suggests that negative life events encountered by the women during period of pregnant were a strong predictors of antenatal depression or postpartum depression [9, 30, 31]. Another meta-analysis consist of 5037 old man also show that the total number of negative life events have the strongest relationship with depression [15].
The finding that physical activity acted as a moderator suggested that the newlyweds performed high and moderate levels of physical activity can be protective from developing a depression symptom in face of negative life events. It is evident that participants with higher PA level had better self-esteem [32], and self-esteem as a psychological resource may enable subjects to cope more effectively with stressful events [33]. Additionally, the people who engaged in physical activity may be more likely to get support from friends and family [34, 35], and study showed that the relationship between negative life events and illness was stronger among subjects with low rather than high levels of social support [36].
Some possible biological pathways can also be suggested to explain why higher level of physical activity can weaken the deleterious effects of negative life events on depression symptom. First, cortisol released from exercising can suppress the subsequent cortisol response to a psychosocial stressor. A randomized controlled trial conducted by Caplin [37] in eighty-three healthy men found that exercise-intensity dampens the HPA-axis stress response in a dose-dependent manner. Second, physical activity is preventive from oxidative stress that associated with depression. A meta-analysis included 30 controlled trials (1346 participants) found that physical training was associated with a significant reduction in pro-oxidant parameters and an increase in antioxidant capacity [38]. In addition, this finding also could be explained by the association between gut microbiota and depressive disorder because exercise may mediate a bidirectional relationship between the gut and brain through alterations in the microbiome [39, 40], although this causal relationship is not clear. Taken together, these evidences support our findings that physical activity plays an moderating role in the association between negative life events and depression symptom among newlyweds.
Several limitations can be taken into account in our study. First, a cross-sectional design of this study will hindered the accurate examination of the causal relationship between life events and depression risk, reverse causation may occur if women with depression symptom have lower physical activity, but it seems to be acceptable in such a large epidemiologic study. Second, the information was collected based on subjective self-reporting, so there might be recall bias in the study. Third, IPAQ-SF is a instrument that only assess the total physical activity level that included the labor- and leisure-related physical activities, however, exercise-or non-exercise-related physical activity may have different effects on mental health. Fourth, some confounding factors had not been assessed, such as resilience resources, which was verified as a moderating factor in the association between negative life event and depression symptom [41]. Of course, the strength of this study was obvious that the multi-centered study with larger sample size yielded a socioeconomically diverse sample.