This prospective study suggests that negative interactions in close relationships may – albeit modestly - contribute to increases in BMI and waist circumference. These effects were not accounted for by socio-demographic characteristics, health behaviors, and common mental disorder. Analyses in repeat data indicated that a long-term exposure to negative aspects (indicated by mean score across 2 study phases) had a slightly stronger effect on weight gain than a single measurement of the exposure.
Our results are in line with previous studies that have suggested a link between poor relationship quality or insufficient social support and obesity; although these studies are limited as they did not specifically measure negative aspects of close relationships, did not assess cumulative exposure, and/or did not measure weight gain (9
). In contrast, in a previous longitudinal study, strain in relations with spouse/partner was not associated with weight gain (12
Potential explanations for the associations between negative aspects of close relationships and weight gain can involve neuroendocrine effects of chronic stress via psychological processes as well as behavioral effects, or both (18
). More specifically, the presence of negative aspects of close relationships can induce psychological processes that are linked to negative appraisals and emotions or low mood. Dysfunctional social relationships may provoke negative feelings (4
), which can increase physiological arousal (5
). Marital strain has been shown to have deleterious effects on cardiovascular, endocrine and immune functions (30
). Dallman et al. (6
) proposed that people might eat high fat and carbohydrate caloric content “comfort food” in an attempt to reduce activity in the corticotrophin-releasing factor (CRF) –driven central chronic stress-response network with its attendant anxiety. Chronic life stress has been associated with a greater preference for energy-dense foods (7
), possibly leading to weight gain in those experiencing chronic stress (31
Furthermore, there may be effects via health behaviors and adherence to medical regimens. For example, the individual may use unhealthy eating and physically inactive lifestyle as adverse coping mechanisms. Psychological and behavioral pathways can also influence each other (32
). However, in the present study an adjustment for health behaviors had little effect on estimates, suggesting that the association between negative aspects of close relationships and weight change may primarily be explained by mechanisms other than those related to health behaviors.
The strengths of this study include the assessment of repeated exposure to negative aspects of close relationships and simultaneous inclusion of a number of covariates. Our study is based on a large well-characterized cohort of British employees and a prospective study design with a median follow-up of 11.2 years. A further strength is that weight, height and waist circumference were directly measured at both examinations (phases 3 and 5) and were not based on questionnaires, thus minimizing the potential of recall bias and misclassification that occur when using self-reports.
However, several limitations need to be taken into account when interpreting the findings. First, our measure of negative aspects of close relationships was self-reported and may thus be influenced by personality traits or specific characteristics of respondents (18
). For example, levels of social support are lower than normal in hostile individuals due to less effective coping strategies in psychosocial stress situations, increasing the likelihood of breakdown of intimate relationships and unhealthy lifestyle (33
). However, it can be argued that it is exactly the subjective experience that gives meaning and significance to social environmental characteristics and that these subjective experiences finally get under one’s skin and/or cause adverse behavioral changes. Therefore, self-rated measures, such as the one being used here, are relevant indicators of social relationships, expressly due to their subjectivity.
Second, our complete case sample included less than half of the original cohort. Loss to follow-up is inevitable in all long-term prospective studies and may lead to biased estimates. We examined potential bias by performing subsidiary analyses with imputed datasets. These analyses suggested that incompleteness of data might have contributed to an overestimation rather than an underestimation of the association between negative aspects of close relationships and weight gain. This finding is important as sample attrition in prospective studies is often speculated to attenuate the effect estimates.
Third, even though we adjusted for a number of possible confounders, the possibility of residual confounding cannot be excluded in observational studies. For example, information was not available on childhood factors (35
) or individual differences in genetic predisposition (36
). Finally, the participants were mostly white, middle-aged civil servants based in the southeast of England, limiting the generalizability of our findings. In other words, there is a need for more diverse samples to extend the validity of our findings.
Despite these limitations, our results suggest that exposure to negative aspects of close relationships is associated with an increased risk of weight gain. The present study adds to the evidence that the development of obesity may be related to social environment in which people live. Future research is needed to study the specific biological, behavioral and psychological mechanisms linking social environmental factors to weight gain and whether interventions designed to improve social relationships could decrease obesity risk.