In this nationally representative cohort of US adults followed longitudinally over 9 years, psychosocial stress was associated with greater weight gain among both men and women with higher baseline body mass indexes if they experienced job-related demands, had difficulty paying bills, or had depression or generalized anxiety disorder. Among women with higher baseline body mass indexes, perceived constraints in life and strain in relations with family also were associated with greater weight gain. Among men with higher baseline body mass indexes, lack of skill discretion or decision authority at work was associated with greater weight gain.
These findings extend prior cross-sectional and longitudinal research by providing an expanded view of associations between psychosocial stress and weight gain in a nationally representative cohort of adults in the United States. Several studies have demonstrated heterogeneity in eating behaviors in response to stress; some people eat more when stressed while others eat less (30
). Laboratory and observational studies of stress and eating behavior have shown inconsistent results when stratified by baseline weight (27
). In our study, with a long follow-up period and diverse measures of psychosocial stress, subjects with higher body mass indexes at baseline who reported greater psychosocial stress gained more weight, whereas this pattern was not evident for those with lower baseline body mass indexes.
Our results also highlight apparent sex differences in the influence of stress on weight gain. Some stressors outside of work or finances, including general life constraints and strain in relationships with family, were associated with weight gain among women but not among men, suggesting effects on weight from a broader range of life domains in women. Prior cross-sectional studies have shown some differential effects by sex. These studies assessed fewer measures of stress than our study evaluated and provided only limited information about specific types of stressors that might differentially influence weight gain (14
Analyses from the 3 prior longitudinal studies were stratified by sex. In the Whitehall study of British civil servants, Kivimaki et al. (11
) found that men with higher baseline body mass indexes gained weight over 5 years if they experienced higher levels of work stress, but men with lower body mass indexes were more likely to lose weight under stressful job circumstances. Among women, weight gain was associated with higher job demands in main effect models, but the association was no longer significant when an interaction with baseline body mass index was included. In the subsequent analysis of the same cohort, men with chronically elevated levels of job strain and low social support at work were more likely to become obese and to develop a high waist circumference than those with no job strain (15
); these associations were not significant among women.
Van Strien et al. (16
) prospectively evaluated the influence of negative life events in a cohort in the Netherlands. Men classified as highly “emotional eaters” gained weight for up to 2 years after the occurrence of a negative life event. No correlation was observed for women. In a large cohort study of monozygotic and same-sex dizygotic Finnish twins, Korkeila et al. (17
) assessed associations of stress and personality type at baseline with weight gain of greater than 10 kg after follow-up of 6 years and 15 years. The only significant adjusted associations were between neuroticism and weight gain after 6 years among older women and between extroversion and less weight gain among younger men.
Stress appears to influence eating behaviors differently by sex as well. In a study of high school students aged 15–19 years, caloric consumption increased on days with stressful events for girls but not for boys (though boys did increase their fat intake) (9
). Similarly, among college students, women consumed more calories than men when exposed to a stressful film (8
Our study found an association between baseline depression and anxiety and weight gain among men and women with higher baseline body mass indexes. Prior evidence has linked depression with the development of obesity, specifically among children and adolescents (35
). Investigations of the relation between anxiety and weight gain have shown mixed results. Some studies have shown associations between anxiety at baseline and weight gain among men (39
) and women (38
), yet another study found a trend toward decreased likelihood of becoming overweight among men and women with anxiety at baseline (40
). None of these studies of depression and anxiety have assessed the effect modification of baseline body mass index.
Several pathways have been explored in animal models to assess how psychosocial stress may influence weight gain. Social subordination in several species of primates induces chronically elevated cortisol levels, and high cortisol levels are associated with abdominal obesity in both nonhuman primates and humans (41
). As a result, social subordination has been examined as a model for stress-induced eating and weight gain. Female monkeys who are socially subordinate have higher levels of abdominal obesity than socially dominant females (44
). In an observational study of macaques, Wilson et al. (45
) found that socially subordinate females consumed more calories and fed more frequently than socially dominant females. The subordinate females also demonstrated more anxious behavior and had alternations of the hypothalamic-pituitary axis with less negative feedback from elevated glucocorticoid levels. Laboratory studies in rats have shown that mild stress (e.g., tail pinching or restraint) can lead to weight gain if highly palatable foods are provided, but not with regular diets (46
Based in large part on animal models, a complex interplay of hormones such as glucocorticoids and ghrelin (that increase appetite) and corticotrophin-releasing hormone and leptin (that decrease appetite) has been proposed by other researchers (48
) to be involved in the physiologic pathways between stress and weight gain. Endogenous opiates induced by eating might also serve a role in limiting the dysphoric effects of stress (52
). These pathways suggest a “comfort food” or “emotional eating” paradigm that has been proposed to explain stress-induced eating and weight gain (53
). The influence of stress on weight gain, therefore, may depend on the intensity and duration of stress and the types of food that are available for consumption.
Few mechanistic studies have assessed hormonal pathways that could link stress and weight in humans. Normal-weight women with major depression had more than twice the cortisol level and intraabdominal fat as those without depression (55
). In a laboratory experiment with postmenopausal women subjected to a stress-inducing protocol, Epel et al. (56
) discovered that women with high waist/hip ratios, regardless of body mass index, were more likely to display higher stress-induced cortisol levels. Women with high waist/hip ratios also felt more threatened under stress, and controlling for this high threat appraisal partially attenuated the association between waist/hip ratio and cortisol. Additional studies have documented higher snack food consumption in women with high stress-induced cortisol levels (12
Our study had several potential limitations. First, there was only 1 follow-up measure of body mass index over a mean of 9.2 years. Psychosocial stress could change over this time period, though there was a moderately high degree of correlation between baseline and follow-up psychosocial stress. Second, although our study cohort was representative of US adults, the response rate to the follow-up survey in our sample was 60%, and nonrespondents differed from respondents on several demographic and health characteristics. However, models were adjusted for the variables that differed between respondents and nonrespondents, and further bias would only arise if the relation of stress and weight change also differed for these 2 groups. Third, certain medications can be associated with weight gain (57
). However, the MIDUS survey did not collect specific drug names, so we could not control for active use of these medications. Nonetheless, in all models, we controlled for diabetes, generalized anxiety disorder, and depression, conditions which are commonly treated with medications that are associated with weight gain. The most commonly used medications for depression and generalized anxiety disorder, selective serotonin reuptake inhibitors, have mixed effects on weight, so the net effect of these medications on weight gain may be limited (57
). Fourth, causality cannot be established in our data despite the temporal ordering of baseline stress and subsequent weight gain. Fifth, weight and height were self-reported in this study and thus could be biased. Other studies have reported a high correlation between self-reported weight and height and measured body mass index (17
), and the prevalence of obesity and overweight in our sample was consistent with reported national estimates (26
). Furthermore, in the subset of 464 subjects in our sample who had height and weight objectively measured at follow-up, the correlation between self-reported and measured body mass index in 2004 exceeded 0.92 for both men and women. Finally, the number of significant interactions found (12 of 22 tested at the 0.05 level, all in the same direction) exceeded what would be expected by chance, and the pattern was consistent with prior evidence.
In this nationally representative cohort, several domains of psychosocial stress as well as anxiety and depression were associated with weight gain among men and women with higher body mass indexes. Awareness of these associations may enable clinicians to help their overweight and obese patients avoid gaining further weight during stressful periods. Stress reduction may also be an important component of weight-loss interventions in worksites and in clinical and public health programs (61