Impact of Smoking and Preexisting Illness on Estimates of the Fractions of Deaths Associated with Underweight, Overweight, and Obesity in the US Population

National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD 20782, USA.
American Journal of Epidemiology (Impact Factor: 5.23). 11/2007; 166(8):975-82. DOI: 10.1093/aje/kwm152
Source: PubMed


Studies of body weight and mortality sometimes exclude participants who have ever smoked or who may have had preexisting illness
at baseline. This exclusionary approach was applied to data from the National Health and Nutrition Examination Surveys to
investigate the potential effects of smoking and preexisting illness on estimates of the attributable fractions of US deaths
in 2000 that were associated with different levels of body mass index (BMI; weight (kg)/height (m)2). Synthetic estimates were calculated by using postexclusion relative risks for BMI categories in place of BMI relative risks
from the full sample, holding the relative risks for all other covariates constant. When the postexclusion relative risks
were used, the attributable fractions of deaths associated with underweight and with higher levels of obesity increased slightly
and the attributable fractions of deaths associated with overweight and with grade 1 obesity decreased slightly. The relative
risks for BMI categories did not show large or systematic changes after simultaneous exclusion of ever smokers, persons with
a history of cancer or cardiovascular disease, and persons who died early in the follow-up period or had their heights and
weights measured at older ages. These analyses suggest that residual confounding by smoking or preexisting illness had little
effect on previous estimates of attributable fractions from nationally representative data with measured heights and weights.

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Available from: Katherine Mayhew Flegal, Jan 05, 2014
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    • "Few studies reported an increased risk of CVD [5,9] or cancer mortality [1] related to underweight. Due to the fact that some diseases can simultaneously cause weight loss and increase mortality risk, reverse causation by preexisting illness has been proposed to explain the association between underweight and increased mortality [1,5,10,11]. Analyses without the five first years of follow-up only marginally changed our results, indicating that only few people had a severe disease when they were included in the study. "
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    ABSTRACT: In contrast to obesity, information on the health risks of underweight is sparse. We examined the long-term association between underweight and mortality by considering factors possibly influencing this relationship. We included 31,578 individuals aged 25-74 years, who participated in population based health studies between 1977 and 1993 and were followed-up for survival until 2008 by record linkage with the Swiss National Cohort (SNC). Body Mass Index (BMI) was calculated from measured (53% of study population) or self-reported height and weight. Underweight was defined as BMI < 18.5kg/m2. Cox regression models were used to determine mortality Hazard Ratios (HR) of underweight vs. normal weight (BMI 18.5- < 25.0kg/m2). Covariates were study, sex, smoking, healthy eating proxy, sports frequency, and educational level. Underweight individuals represented 3.0% of the total study population (n = 945), and were mostly women (89.9%). Compared to normal weight, underweight was associated with increased all-cause mortality (HR: 1.37; 95%CI: 1.14-1.65). Increased risk was apparent in both sexes, regardless of smoking status, and mainly driven by excess death from external causes (HR: 3.18; 1.96-5.17), but not cancer, cardiovascular or respiratory diseases. The HR were 1.16 (0.88-1.53) in studies with measured BMI and 1.59 (1.24-2.05) with self-reported BMI. The increased risk of dying of underweight people was mainly due to an increased mortality risk from external causes. Using self-reported BMI may lead to an overestimation of mortality risk associated with underweight.
    Full-text · Article · Apr 2014 · BMC Public Health
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    • "Consistent with the statistical explanation, numerous studies find significantly stronger mortality risks of obesity after implementing measures aimed at reducing reverse causality, such as restricting samples to “healthy” participants and delaying onset of risk for several years after the time of the survey [9,10]. These strategies, however, have been criticized on several grounds: the exclusions lead to eliminating a large proportion of deaths among respondents, thereby reducing the generalizability of findings [11]. Also, pre-existing illness is identified on the basis of respondent self-reports, meaning that individuals with undiagnosed illnesses cannot be excluded. "
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    ABSTRACT: The high prevalence of disease and associated weight loss at older ages limits the validity of prospective cohort studies examining the association between body mass index (BMI) and mortality. I examined mortality associated with excess weight using maximum BMI--a measure that is robust to confounding by illness-induced weight loss. Analyses were carried out on US never-smoking adults ages 50-84 using data from the National Health and Nutrition Examination Surveys (1988-1994 and 1999-2004) linked to the National Death Index through 2006. Cox models were used to estimate hazard ratios for mortality according to BMI at time of survey and at maximum. Using maximum BMI, hazard ratios for overweight (BMI, 25.0-29.9 kg/m2), obese class 1 (BMI, 30.0-34.9 kg/m2) and obese class 2 (BMI, 35.0 kg/m2 and above) relative to normal weight (BMI, 18.5-24.9 kg/m2) were 1.28 (95% confidence interval [CI], 0.89-1.84), 1.67 (95% CI, 1.15-2.40), and 2.15 (95% CI, 1.47-3.14), respectively. The corresponding hazard ratios using BMI at time of survey were 0.98 (95% CI, 0.77-1.24), 1.18 (95% CI, 0.91-1.54), and 1.31 (95% CI, 0.95-1.81). The percentage of mortality attributable to overweight and obesity among never-smoking adults ages 50-84 was 33% when assessed using maximum BMI. The comparable figure obtained using BMI at time of survey was substantially smaller at 5%. The discrepancy in estimates is explained by the fact that when using BMI at time of survey, the normal category combines low-risk stable-weight individuals with high-risk individuals that have experienced weight loss. In contrast, only the low-risk stable-weight group is categorized as normal weight using maximum BMI. Use of maximum BMI reveals that estimates based on BMI at the time of survey may substantially underestimate the mortality burden associated with excess weight in the US.
    Full-text · Article · Mar 2014 · Population Health Metrics
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    • "( ≥70 y SALSA ) McAuley et al , 25 2010 Seccareccia et al , 43 1998 ( women 45 - 69 y ) Tice et al , 46 2006 Arndt et al , 39 2007 Walter et al , 48 2009 ( disabled ) Sui et al , 41 2007 Hanson et al , 44 1995 Fontaine et al , 40 2012 ( 60 - 70 y SALSA ) Locher et al , 81 2007 Fontaine et al , 40 2012 ( ≥70 y SAHS ) Fontaine et al , 40 2012 ( 60 - 70 y SAHS ) Seccareccia et al , 43 1998 ( women 20 - 44 y ) Petursson et al , 47 2011 ( women ) Seccareccia et al , 43 1998 ( men 45 - 69 y ) Lang et al , 23 2008 ( men ) Fontaine et al , 40 2012 ( 18 <60 y SAHS ) Flegal et al , 30 2007 ( ≥70 y ) Walter et al , 48 2009 ( nondisabled ) Petursson et al , 47 2011 ( men ) McTigue et al , 68 2006 ( whites ) Flegal et al , 30 2007 ( 60 - 69 y ) Greenberg et al , 54 2007 Sonestedt et al , 110 2011 Flegal et al , 30 2007 ( 25 - 59 y ) Lang et al , 23 2008 ( women ) Katzmarzyk et al , 77 2001 Katzmarzyk et al , 74 2012 McTigue et al , 68 2006 ( blacks ) Data markers indicate hazard ratios and error bars indicate 95% confidence intervals . SAHS indicates San An - tonio Heart Study ; and SALSA , Sacramento Area Latino Study on Aging . "
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    ABSTRACT: Estimates of the relative mortality risks associated with normal weight, overweight, and obesity may help to inform decision making in the clinical setting. To perform a systematic review of reported hazard ratios (HRs) of all-cause mortality for overweight and obesity relative to normal weight in the general population. PubMed and EMBASE electronic databases were searched through September 30, 2012, without language restrictions. Articles that reported HRs for all-cause mortality using standard body mass index (BMI) categories from prospective studies of general populations of adults were selected by consensus among multiple reviewers. Studies were excluded that used nonstandard categories or that were limited to adolescents or to those with specific medical conditions or to those undergoing specific procedures. PubMed searches yielded 7034 articles, of which 141 (2.0%) were eligible. An EMBASE search yielded 2 additional articles. After eliminating overlap, 97 studies were retained for analysis, providing a combined sample size of more than 2.88 million individuals and more than 270,000 deaths. Data were extracted by 1 reviewer and then reviewed by 3 independent reviewers. We selected the most complex model available for the full sample and used a variety of sensitivity analyses to address issues of possible overadjustment (adjusted for factors in causal pathway) or underadjustment (not adjusted for at least age, sex, and smoking). Random-effects summary all-cause mortality HRs for overweight (BMI of 25-<30), obesity (BMI of ≥30), grade 1 obesity (BMI of 30-<35), and grades 2 and 3 obesity (BMI of ≥35) were calculated relative to normal weight (BMI of 18.5-<25). The summary HRs were 0.94 (95% CI, 0.91-0.96) for overweight, 1.18 (95% CI, 1.12-1.25) for obesity (all grades combined), 0.95 (95% CI, 0.88-1.01) for grade 1 obesity, and 1.29 (95% CI, 1.18-1.41) for grades 2 and 3 obesity. These findings persisted when limited to studies with measured weight and height that were considered to be adequately adjusted. The HRs tended to be higher when weight and height were self-reported rather than measured. Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality. The use of predefined standard BMI groupings can facilitate between-study comparisons.
    Full-text · Article · Jan 2013 · JAMA The Journal of the American Medical Association
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