Hailey R. Banack

The obesity paradox: Understanding the effect of obesity on mortality among individuals with cardiovascular disease

OBJECTIVE To discuss possible explanations for the obesity paradox and explore whether the paradox can be attributed to a form of selection bias known as collider stratification bias. METHOD The paper is divided into three parts. First, possible explanations for the obesity paradox are reviewed. Second, a simulated example is provided to describe collider stratification bias and how it could generate the obesity paradox. Finally, an example is provided using data from 17,636 participants in the US National and Nutrition Examination Survey (NHANES III). Generalized linear models were fit to assess the effect of obesity on mortality both in the general population and among individuals with diagnosed cardiovascular disease (CVD). Additionally, results from a bias analysis are presented. RESULTS In the general population, the adjusted risk ratio relating obesity and all-cause mortality was 1.24 (95% CI 1.11, 1.39). Adjusted risk ratios comparing obese and non-obese among individuals with and without CVD were 0.79 (95% CI 0.68, 0.91) and 1.30 (95% CI=1.12, 1.50), indicating that obesity has a protective association among individuals with CVD. CONCLUSION Results demonstrate that collider stratification bias is one plausible explanation for the obesity paradox. After conditioning on CVD status in the design or analysis, obesity can appear protective among individuals with CVD.

PTSD following childbirth: a prospective study of incidence and risk factors in Canadian women.

OBJECTIVE The goals of the present study were to estimate the incidence and course of full and partial Post-Traumatic Stress Disorder (PTSD) following childbirth and to prospectively identify factors associated with the development of PTSD symptoms at 1month following childbirth. METHODS The sample comprised 308 women, with assessments at four time points: 25-40weeks gestation, 4-6weeks postpartum, 3 and 6months postpartum. Current and prior PTSD were assessed by the Structured Clinical Interview for DSM-IV (SCID-I) and the Modified PTSD Symptom Scale Self-Report (MPSS-SR). RESULTS Incidence rates of PTSD varied according to time of measurement and instrument used, with higher rates of full and partial PTSD using the MPSS-SR at 1month postpartum (7.6% and 16.6%, respectively). Multivariate logistic regression showed that higher anxiety sensitivity (OR=1.75; 95% CI=1.19‒2.57, p=.005), history of sexual trauma (OR=2.81; 95% CI=1.07‒7.37, p=.036), a more negative childbirth experience than expected (OR=0.96; 95% CI=0.94‒0.98, p=.001), and less available social support at 1month postpartum (OR=0.40; 95% CI=0.17‒0.96, p=.041) independently predicted full or partial PTSD at 1month following childbirth. CONCLUSION Our results indicate that a history of sexual trauma and anxiety sensitivity can increase the probability of developing PTSD after childbirth. The findings highlight the importance of screening and providing more tailored services for women at high risk.

Does selection bias explain the obesity paradox among individuals with cardiovascular disease

OBJECTIVES The objectives of this article are to demonstrate that the obesity paradox may be explained by collider stratification bias and to estimate the biasing effects of unmeasured common causes of cardiovascular disease (CVD) and mortality on the observed obesity-mortality relationship. METHODS We use directed acyclic graphs, regression modeling, and sensitivity analyses to explore whether the observed protective effect of obesity among individuals with CVD can be plausibly attributed to selection bias. Data from the third National Health and Examination Survey was used for the analyses. RESULTS The adjusted total effect of obesity on mortality was a risk difference (RD) of 0.03 (95% confidence interval [CI]: 0.02, 0.05). However, the controlled direct effect of obesity on mortality among individuals without CVD was RD = 0.03 (95% CI: 0.01, 0.05) and RD = -0.12 (95% CI: -0.20, -0.04) among individuals with CVD. The adjusted total effect estimate demonstrates an increased number of deaths among obese individuals relative to nonobese counterparts, whereas the controlled direct effect shows a paradoxical decrease in morality among obese individuals with CVD. CONCLUSIONS Sensitivity analysis demonstrates unmeasured confounding of the mediator-outcome relationship provides a sufficient explanation for the observed protective effect of obesity on mortality among individuals with CVD.

Should Patients with Chronic Disease Be Told to Gain Weight? The Obesity Paradox and Selection Bias

Obesity is associated with lower mortality in individuals with chronic disease.(1) This counterintuitive inverse association—the “obesity paradox”(2)—has been described in patients with cardiovascular disease, diabetes, hip fracture and even Chagas’ disease. If obese individuals with chronic diseases live longer, should we start advising them to gain rather than lose weight?

The association between sleep disturbance, depressive symptoms, and health-related quality of life among cardiac rehabilitation participants.

PURPOSE: Recent guidelines from the Canadian Association of Cardiac Rehabilitation highlight the importance of addressing sleep disturbance among participants of cardiac rehabilitation (CR) programs. The primary objective of this study was to examine the relationship between depressive symptoms, health-related quality of life, and sleep disturbance in CR participants. The secondary objective was to estimate the prevalence of sleep disturbance among CR participants with and without depressive symptoms and explore demographic, medical, and psychological predictors of poor sleep quality. METHODS: Cardiac rehabilitation participants (N = 259) were included in this study. Participants completed a standardized questionnaire package including demographic, health-related, and psychosocial measures. Physiologic and anthropometric measurements were taken at baseline. Descriptive statistics were calculated for all variables, and data were analyzed using multivariate logistic regression. RESULTS: Poor sleep quality was reported by 52% of participants in the sample, and 47% of participants in the sample reported experiencing at least mild depressive symptoms. Poor sleep occurred more often in individuals with depressive symptoms, and after adjustment for medical factors and health-related quality of life, participants with symptoms of depression were still more likely to experience sleep disturbance than those without depressive symptoms (OR = 2.80; 95% CI, 1.37–5.77). An important gender difference emerged in the relationship between symptoms of depression and sleep disturbance. CONCLUSION: Among participants of a CR program, disturbed sleep was strongly associated with depressive symptoms and decreased health-related quality of life. Results demonstrate the importance of sleep evaluation in CR programs.

Selection bias: A missing factor in the obesity paradox debate

Dear Drs. Ravussin and Ryan: The September issue of Obesity featured articles by Tobias and Hu (1) and Flegal and KalantarZadeh (2) that explored the observation that, in clinical populations, such as individuals with heart failure, chronic kidney disease, or diabetes, those with higher BMI often have lower mortality rates than leaner individuals. The articles disagree whether this phenomenon, known as the obesity paradox, is a true causal effect. Flegal and KalantarZadeh assert that the research on the obesity paradox is consistent with greater BMI conferring “modest survival advantages” (2). Tobias and Hu disagree, arguing that the obesity paradox is likely an “artifact of methodological limitations” (1).

Estimating the Time-Varying Joint Effects of Obesity and Smoking on All-Cause Mortality Using Marginal Structural Models

Obesity and smoking are independently associated with a higher mortality risk, but previous studies have reported conflicting results about the relationship between these 2 time-varying exposures. Using prospective longitudinal data (1987-2007) from the Atherosclerosis Risk in Communities Study, our objective in the present study was to estimate the joint effects of obesity and smoking on all-cause mortality and investigate whether there were additive or multiplicative interactions. We fit a joint marginal structural Poisson model to account for time-varying confounding affected by prior exposure to obesity and smoking. The incidence rate ratios from the joint model were 2.00 (95% confidence interval (CI): 1.79, 2.24) for the effect of smoking on mortality among nonobese persons, 1.31 (95% CI: 1.13, 1.51) for the effect of obesity on mortality among nonsmokers, and 1.97 (95% CI: 1.73, 2.22) for the joint effect of smoking and obesity on mortality. The negative product term from the exponential model revealed a submultiplicative interaction between obesity and smoking (β = -0.28, 95% CI: -0.45, -0.11; P < 0.001). The relative excess risk of interaction was -0.34 (95% CI: -0.60, -0.07), indicating the presence of subadditive interaction. These results provide important information for epidemiologists, clinicians, and public health practitioners about the harmful impact of smoking and obesity.

Promoting Long Term Athlete Development in Cross Country Skiing Through Competency-Based Coach Education: A Qualitative Study

Coach education programs in Canada and abroad have recently been framed around Long Term Athlete Development (LTAD), a seven-stage model that is based on the physical, mental, emotional, and cognitive development of children and adolescents. To date, limited empirical research on LTAD exists. The primary objective of this study was to identify whether individuals who completed a coach education course acquired an understanding of LTAD and whether they integrated this knowledge into their coaching practice. The secondary purpose was to identify information that could be used to improve the coach education program as well as the effectiveness of youth sport coaching in cross-country skiing. Results indicated the course was an effective technique for delivering the core principles of LTAD to coaches with little or no prior knowledge of the concept. As well, coaches successfully integrated the principles of LTAD into their coaching practices. These results are discussed in regard to improving the effectiveness of youth sport coaching.

Perhaps the correct answer is: (D) all of the above.

We are grateful to nguyen et al and Glymour and Vittinghoff for their interest in our research letter and for the opportunity to respond to their remarks. Specifically, we focus on the argument raised by nguyen and colleagues that much of the debate in the obesity paradox literature can be attributed to confusion between total and direct effects, as well as the related point made by Glymour and Vittinghoff that the selection bias correction described in our letter does not answer the key question surrounding the obesity paradox. The goal of our letter was to address the multitude of published studies that use a cohort of patients with diagnosed chronic disease (such as heart failure) and attempt to answer the question of whether obesity is protective or harmful in this selected subgroup. By conditioning on disease status through restriction of the study cohort, we reasoned that these articles must necessarily induce collider stratification bias because of the presence of unmeasured common causes of chronic disease and mortality (Figure). As other authors have previously noted, the causal effect estimate sought in these studies is akin to a controlled direct effect:

Changing Surgeons Improves Outcome of Subsequent Primary Total Joint Arthroplasty in Previously Dissatisfied Patients

We assessed whether patients who were dissatisfied with their previous primary hip (THA) or knee (TKA) arthroplasty, done by another surgeon, would have continued dissatisfaction or would have significant improvements in outcome scores following their subsequent primary THA or TKA. The majority of reasons provided for switching surgeons and/or institutions related to dissatisfaction with some aspect of their surgical experience specifically involving the surgeon-patient interaction itself. All 12 THA and TKA patients noted that their subsequent arthroplasty had decreased their pain, improved their function and that they were satisfied with their result. All patients had a statistically significant improvement in their Harris Hip Score or Knee Society Score, WOMAC and SF-36 questionnaires. This study demonstrates that previous dissatisfaction with a THA or THA does not predispose to a suboptimal outcome following subsequent primary hip or knee arthroplasty.