Stress and Obesity: Partners in Disease

Introduction

Best Evidence Reference

Brunner EJ, Chandola T, Marmot MG. Prospective effect of job strain on general and central obesity in the Whitehall II Study. Am J Epidemiol. 2007;165:828-837. Abstract

This study was selected from Medscape Best Evidence, which uses the McMaster Online Rating of Evidence System. Of a possible top score of 7, this study was ranked as 6 for newsworthiness and 5 for relevance by clinicians who used this system.

Commentary

Obesity is a burgeoning problem in the developed world, and certain behaviors, such as increased portion sizes and reduced physical activity, can help explain why the obesity epidemic is spreading. Job strain might also contribute to the prevalence of obesity, and the current study addresses this issue in a cohort of civil servants followed over time.

Obesity continues to be one of the largest public health concerns of the developed world. Analysis of data from the 2001-2002 National Health and Nutrition Examination Survey (NHANES) found that the prevalence rates of overweight and obesity among US adults were 31.5% and 30.5%, respectively.^[1] The prevalence of overweight in children was 16.5%. Compared to the previous NHANES survey (1988-1994), the body mass index (BMI) greater than 30 among adults had doubled.^[2] (Of note, the prevalence of overweight and obesity were fairly stable between the 1999-2000 and 2001-2002 examination periods.)

While the problem of obesity has been well publicized, clinicians should also understand that societal factors play a prominent role in obesity. In research sponsored by the World Health Organization involving 26 different populations worldwide, surveys of over 30,000 subjects found an inverse trend between BMI and highest educational level attained.^[3] Women with lower educational attainment were significantly more likely to be obese compared with men with similar educational backgrounds, although lower educational levels in both sexes were associated with higher obesity. Moreover, the negative association between educational attainment and obesity increased over the 10-year study period, indicating that the obesity gap between well-educated and poorly educated individuals was increasing. To reinforce these data, another study limited to developed countries found that increased income disparity was associated with not only higher rates of obesity, but also diabetes mortality as well among subjects at the lower end of the income scale.^[4]

Other societal trends can affect obesity as well. In the United States, more individuals are choosing to eat at restaurants than at home, and the easiest and least expensive option in dining is often preferred. Such choices can increase the risk of developing obesity. Ecological research from 21 developed countries found that girls who ate fast food at least twice a week were more likely to become obese compared with those who ate fast food less frequently.^[5] Unfortunately, the assimilation of other cultures into American society may not help improve the obesity problem. In 1 study, while regularly eating at fast food restaurants increased the risk of overweight in adults and children in Mexican-American families by a factor of 2.2, the risk of overweight associated with eating at buffet-style restaurants was slightly worse (odds ratio = 2.8).^[6] Families who ate food at Mexican restaurants, however, were less likely to be overweight.

The work environment can contribute to obesity as well. In a study of 208 male workers in Japan, obesity was associated with psychological tension and anxiety, much of which was derived from high demands and poor decision latitude at work.^[7] The authors also found that higher degrees of stress negatively affected subjects' diets, which contributed to higher rates of obesity.

The current study examined the 10,308 civil servants from the Whitehall II study, all of whom were between the ages of 35 and 55. Work stress was assessed by the Job Strain Questionnaire and defined by poor work social support, high job demands, and low job control. Overall, work strain was associated with increased risk of BMI obesity by a maximum odds ratio of 1.73, and of waist obesity by a maximum odds ratio of 1.61. There was a dose-response relationship between the number of reports of stress and obesity.

There were some interesting nuances related to the study's main finding. Men were more likely than women to suffer the negative effects of job strain in terms of obesity, to the point that women did not experience a significant increase in waist obesity with stress. Overall, poor social support at work was the most important singular factor of job strain in increasing the risk of obesity in this study.

The study was strengthened by analyzing individuals prospectively over time and employing repeated measures of job stress as participants advanced through their careers. However, the study was limited by examining a very specific group of employees -- civil servants -- in a first-world country.

Obesity may just be a part of the overall increased health risk associated with work stress, with the sum of these risks being an increased prevalence of cardiovascular disease. In a study of nearly 7000 individuals, the prevalence of smoking was elevated among subjects with greater job strain, while men with low degrees of decision latitude were also more likely to be sedentary.^[8] However, no job environment factor in this study was independently related to increased BMI.

A case-control analysis of 609 workers in France found that job strain increased the risk of developing hypertension. The odds ratios for hypertension associated with job strain were 3.20 in women and 2.60 in men. Low social support at work was not related to hypertension, and, moreover, higher levels of social support did not mitigate the effects of job strain on hypertension.^[9] Another study of female nurses and male factory workers generally corroborated these results. Researchers found that increased duration of shifts during work was associated with increased systolic blood pressure among men over age 30.^[10] Both BMI and waist-to-hip ratio increased with increasing shift duration among nurses.

The study of nurses and factory workers failed to find an association between blood glucose levels and the duration of shift work. In another analysis of the Nurses' Health Study II cohort, working overtime was associated with an increased risk of developing type 2 diabetes, while women who worked less than 20 hours per week had a lower risk of diabetes.^[11]

There is also evidence that serum markers associated with an increased risk of cardiovascular disease may increase with job stress. A study of adults in Sweden found that men reporting high effort and low reward at work had increased levels of total cholesterol and the total cholesterol/high-density lipoprotein cholesterol ratio after adjustment for possible confounders.^[12] Women whose jobs required more effort had higher levels of low-density lipoprotein cholesterol.

The association between stress at work and cardiovascular risk factors such as BMI, hypertension, and lipid levels points to a possible larger relationship between work stress and cardiovascular disease. The researchers of the Whitehall study have previously examined this issue in their study cohort.^[13] They demonstrated that the hazard ratio for coronary heart disease was increased with low decision latitude among men (adjusted hazard ratio 1.43), but low decision latitude did not significantly increase the risk of coronary heart disease among women. However, both men and women experienced increased risks of coronary heart disease with higher demands at work. This increased risk of coronary heart disease was increased with job stress at all employment grades in the organization. This research echoed previous studies in that greater social support at work failed to improve cardiovascular outcomes associated with significant job stress.

The effects of stress at work constitute a major public health issue. As clinicians, the best we can do is counsel patients about the potential cardiovascular and metabolic events associated with high levels of stress and encourage healthy life choices for patients at risk. While it may be unrealistic to ask employers to reduce job stress at all levels in our competitive economy, these same employers should understand that their employees' health is critical to their success. There is a dearth of data regarding stress reduction programs at work and cardiovascular outcomes, and future researchers should address this issue.