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  • Despite intense scrutiny of the harms from

    2018-11-05

    Despite intense scrutiny of the harms from smoking, we are not aware of a prior study that has investigated, using data at the individual level, whether the risks of death from smoking differ across countries. We believe that such comparisons are best assessed on an additive or risk difference scale as we have done. One meta-analysis of 26 studies incorporating populations in the United States, Europe, and Asia concluded that the relative risks of death from smoking did not appear to “vary significantly” by the study population (Shavelle et al., 2008). Our results suggest that at least for the United States and Finland there are significant differences in the risks. Much of the controversy in the obesity-mortality association has focused on the downwardly biasing effects of reverse causation: a bias caused by weight loss due to illness (Hu, 2008; Mehta & Chang, 2009). This selection bias may operate to a differing degree in the U.S. and Finland if the underlying populations have a different distribution of health states. Our study attempted to account for this bias by examining BMI pertaining to early adulthood, which is thought to be more robust to reverse causation compared to BMI at time of survey (Preston et al., 2013). Our findings suggest that both BMI at time of the survey and in early adulthood are positively associated with the risk of dying, whether assessed separately or jointly. This pattern was evident in both the United States and Finland. In addition, the indication that the coefficients for BMI pertaining to early adulthood are larger than the coefficients for BMI at time of survey (Model 6) in both populations suggests that inclusion of earlier life BMI is as important as current BMI to death risks. The main limitation of our approach is that our indicator of earlier life BMI was based on retrospective reports. Similar to our study, the Prospective Studies Collaboration pooled individual-level data to investigate the association between BMI and mortality (Prospective Studies Collaboration, 2009). Data were drawn from national and convenience samples from 57 datasets from Western Europe and the United States. The study reported no statistically significant heterogeneity across the studies in the relative risks of ischemic brompheniramine maleate disease death from high BMI. Unlike the PSC (2009) study, we accounted for confounding by educational level, quantified time trends in the risks, and included BMI in early adulthood in addition to BMI at time of survey. We did not find evidence that the risks of death from obesity were changing in either country. Previously, Mehta and Chang (2011b) reported declines over two time periods (1971–1987 and 1988–2006) in the relative risks of death from obesity in the United States for individuals of all race/ethnicities at ages 50–74 at study entry in the NHANES 1 and NHANES 3 (Mehta & Chang, 2011b). Our study was limited to whites and used a different entry age range of 30–69 and additional NHANES datasets (we included NHANES 2). Mehta and Chang (2011b) also observed declining relative risks over time in the U.S. National Health Interview Survey and the Framingham Heart Study. Declining relative risks, however, have not been documented universally and our study raises further uncertainty on this question. Calle, Teras, and Thun (2005) reported no decline in the relative risks of death from obesity among adult nonsmokers between 1982 and 1998 in the U.S. Cancer Prevention Study II. Yu (2012) also using NHANES, examined age, period, and cohort variations in the relative risks from obesity and found evidence that the relative risks increased in earlier compared to more recent cohorts. We are not aware of any existing studies on other high-income countries examining whether risks of death from obesity are changing. Given the diverging findings and lack of research in other countries, additional studies of this question are warranted. The role of medical care in reducing the death risks from obesity is also understudied. At least in the United States, evidence suggests that over time the obese population may have disproportionately benefitted from improved control of cardio-metabolic risk factors as, for example, high cholesterol (Gregg et al., 2005). Other research indicates that healthcare providers may have become more aggressive in risk-factor control for obese patients compared to non-obese patients (Chang, 2010). Cross-national comparisons in cardio-metabolic risk factor control and quality of care among the obese may yield insights into whether some nations have been successful in reducing the death risks from obesity through medical interventions. Our findings suggest that at least between the United States and Finland, two countries with distinct healthcare delivery systems, the death risks from obesity are highly similar.