Job strain and changes in the body mass index among working women: a prospective study

The relationship between job strain and weight gain has been unclear, especially for women. Using data from over 52,000 working women, we compare the association between change in job strain and change in body mass index (BMI) across different levels of baseline BMI.

We used data from participants in the Nurses' Health Study II (n=52,656, mean age=38.4 years), an ongoing prospective cohort study. Using linear regression, we modeled the change in BMI over 4 years as a function of the change in job strain, baseline BMI and the interaction between the two. Change in job strain was characterized in four categories combining baseline and follow-up levels as follows: consistently low strain (low at both points), decreased strain (high strain at baseline only), increased strain (high strain at follow-up only) and consistently high strain (high at both points). Age, race/ethnicity, pregnancy history, job types and health behaviors at baseline were controlled for in the model.

In adjusted models, women who reported high job strain at least once during the 4-year period had a greater increase in BMI (ΔBMI=0.06-0.12, P<0.05) compared with those who never reported high job strain. The association between the change in job strain exposure and the change in BMI depended on the baseline BMI level (P=0.015 for the interaction): the greater the baseline BMI, the greater the BMI gain associated with consistently high job strain. The BMI gain associated with increased or decreased job strain was uniform across the range of baseline BMI.

Women with higher BMI may be more vulnerable to BMI gain when exposed to constant work stress. Future research focusing on mediating mechanisms between job strain and BMI change should explore the possibility of differential responses to job strain by initial BMI.