摘要：Objectives. We examined the longitudinal effect of obesity, major depression, and their combination on work performance impairment (WPI). Methods. We collected longitudinal data (2004–2013) on 1726 paid employees from the Netherlands Study of Depression and Anxiety at baseline and 2-, 4-, and 6-year follow-up. We defined obesity with body mass index and waist circumference. We diagnosed major depression with the Composite International Diagnostic Interview 2.1. We assessed work performance impairment with a questionnaire for illness-associated costs. We used generalized estimating equations for modeling, and estimated interaction on the additive scale. Results. Obesity, abdominal obesity, and major depression were longitudinally associated with increased risk of high WPI. The combinations of obesity and major depression, and of abdominal obesity and major depression were associated with increased risk of high WPI (odds ratios of 2.36 [95% confidence interval = 1.61, 3.44] and 1.88 [95% confidence interval = 1.40, 2.53], respectively), but the relative excess risks attributable to interaction were nonsignificant. Conclusions. The longitudinal joint effect of obesity and major depression on high WPI implies that obesity intervention may be more beneficial for individuals with major depression than those without regarding risk of high WPI, if confirmed in a large, representative sample. Obesity and major depression are major public health problems, posing enormous challenges in the decades to come. 1,2 Both obesity and major depression increase the risk of adverse health outcomes, such as type 2 diabetes, cardiovascular diseases, premature death, and disability. 1,2 By 2030, major depression is even expected to be one of the top leading causes of disability-adjusted life years in high-income countries. 1 In the European Union area, the costs of depression were estimated at 92 billion euro in 2010, with lost productivity because of absenteeism (being off work because of sickness) and presenteeism (being present at work while ill) representing more than 50% of all costs related to depression. 3 It has been shown that a broad range of occupational health problems including depression is strongly associated with obesity, making obesity a prevailing problem in the working population. 4–6 Previous studies that examined obesity in working populations are mainly focused on absenteeism 7,8 ; less is known about productivity loss at work attributable to obesity. Both obesity and major depression can impair work performance. Work performance impairment (WPI) refers to productivity loss at work because of health problems. Work performance impairment is an increasing problem in aging workforces and has enormous cost implications for individuals, companies, and society as a whole. 9,10 Earlier, cross-sectional studies showed that major depression is associated with high WPI. 11,12 Higher body weight and an excess of visceral fat are also associated with productivity loss. 5–7 However, it is not known whether obesity and major depression jointly affect high WPI and if the risk of major depression on high WPI further increases in obese individuals. There are 3 main reasons to examine their interaction or joint effect on WPI. First, obesity and depression are bidirectionally related, and neither obesity nor major depression fully precedes the other regarding the effect of WPI (i.e., no sole mediation). Then, it would be interesting to examine the joint effect of these 2 risk factors on high WPI and to estimate to what extent their joint effect differs from the sum of their separate effects on high WPI. Second, obesity and major depression share around 12% to 20% pleiotropic genes, and it seems that they might have a common etiology that make them valuable to examine. 13–17 Third, both obesity and depression are associated with a global burden of disease and disability. 1,2 In terms of their effects on the risk of high WPI, obesity and major depression may interact thereby augmenting or reducing the effect of one another. If obesity and major depression exacerbate a common pathway, we expect to observe a substantially elevated risk of WPI in people with both exposures. The interaction between 2 exposures of interest on a certain outcome can best be measured by statistical interaction on the additive scale by using measures such as the relative excess risk due to interaction (RERI) and attributable proportion (AP). 18,19 A statistical interaction on the additive scale is more relevant to disease prevention and workplace health promotion programs in vulnerable workers than an interaction on the multiplicative scale, which is relevant in disease etiology. 18 For example, if the joint effect of obesity and major depression surpasses the sum of their separate effects, then a reduction of either obesity or major depression would also reduce the risk of the other factor regarding high WPI. In terms of clinical decision-making, then someone with major depression can reduce his or her risk regarding high WPI even more by losing weight than someone without major depression. The main objective of the present study was to examine the longitudinal separate and joint effects of obesity and major depression on WPI. We used the RERI and AP as measures to test the hypothesis that the joint effect of obesity and major depression on high WPI is larger than the sum of the separate effects of obesity and major depression on high WPI. To our knowledge, there is no study to date that has investigated this hypothesis.
