Estimating the Effects of Obesity and Weight Change on Mortality Using a Dynamic Causal Model

Sources and severity of bias in estimates of the BMI-mortality association

Estimates of mortality differences by body mass index (BMI) are likely biased by: (1) confounding bias from heterogeneity in body shape; (2) positive survival bias in high-BMI samples due to recent weight gain; and (3) negative survival bias in low-BMI samples due to recent weight loss. I investigate these sources of bias in the National Health and Nutrition Examination Survey (NHANES) 1988-94 and 1999-2006 linked to mortality up to 2015 (17,784 cases; 4,468 deaths). I use Cox survival models to estimate BMI differences in all-cause mortality risks among adults aged [45-85) in the United States. I test for age-based differences in BMI-mortality associations and estimate functional forms of the association using nine BMI levels. Estimates of the BMI-mortality association in NHANES data are significantly affected by all three biases, and obesity-mortality associations adjusted for bias are substantively strong at all ages. The mortality consequences of overweight and obesity have likely been underestimated, especially at older ages.

Lifestyle information and access to a commercial weight management group to promote maternal postnatal weight management and positive lifestyle behaviour: the SWAN feasibility RCT

Background

Increasing numbers of UK women have overweight or obese body mass index scores when they become pregnant, or gain excessive weight in pregnancy, increasing their risk of adverse outcomes. Failure to manage postnatal weight is linked to smoking, non-healthy dietary choices, lack of regular exercise and poorer longer-term health. Women living in areas of higher social deprivation are more likely to experience weight management problems postnatally.

Objectives

The objectives were to assess the feasibility of conducting a definitive randomised controlled trial to determine the clinical effectiveness and cost-effectiveness of lifestyle information and access to a commercial weight management group focusing on self-monitoring, goal-setting and motivation to achieve dietary change commencing 8–16 weeks postnatally to achieve and maintain weight management and positive lifestyle behaviour.

Design

The design was a randomised two-arm feasibility trial with a nested mixed-methods process evaluation.

Setting

The setting was a single centre in an inner city setting in the south of England.

Participants

Participants were women with body mass index scores of > 25 kg/m2 at antenatal ‘booking’ and women with normal body mass index scores (18.0–24.9 kg/m2) at antenatal booking who developed excessive gestational weight gain as assessed at 36 weeks’ gestation.

Main outcome measures

Recruitment, retention, acceptability of trial processes and identification of relevant economic data were the feasibility objectives. The proposed primary outcome was difference between groups in weight at 12 months postnatally, expressed as percentage weight change and weight loss from antenatal booking. Other proposed outcomes included assessment of diet, physical activity, smoking, alcohol consumption, body image, maternal esteem, mental health, infant feeding and NHS costs.

Results

Most objectives were achieved. A total of 193 women were recruited, 98 allocated to the intervention arm and 95 to the control arm. High follow-up rates (> 80%) were achieved to 12 months. There was an 8.8% difference in weight loss at 12 months between women allocated to the intervention arm and women allocated to the control arm (13.0% vs. 4.2%, respectively; p = 0.062); 47% of women in the intervention arm attended at least one weight management session, with low risk of contamination between arms. The greatest benefit was among women who attended ≥ 10 sessions. Barriers to attending sessions included capability, opportunity and motivation issues. Data collection tools were appropriate to support economic evaluation in a definitive trial, and economic modelling is feasible to quantify resource impacts and outcomes not directly measurable within a trial.

Limitations

The trial recruited from only one site. It was not possible to recruit women with normal body mass index scores who developed excessive pregnancy weight gain.

Conclusions

It was feasible to recruit and retain women with overweight or obese body mass index scores at antenatal booking to a trial comparing postnatal weight management plus standard care with standard care only and collect relevant data to assess outcomes. Approaches to recruit women with normal body mass index scores who gain excessive gestational weight need to be considered. Commercial weight management groups could support women’s weight management as assessed at 12 months postnatally, with probable greater benefit from attending ≥ 10 sessions. Process evaluation findings highlighted the importance of providing more information about the intervention on trial allocation, extended duration of time to commence sessions following birth and extended number of sessions offered to enhance uptake and retention. Results support the conduct of a future randomised controlled trial.

Trial registration

Current Controlled Trials ISRCTN39186148.

Funding

This project was funded by the National Institute for Health Research (NIHR) Public Health Research programme and will be published in full in Public Health Research; Vol. 8, No. 9. See the NIHR Journals Library website for further project information.

The Effects of Reverse Causality and Selective Attrition on the Relationship Between Body Mass Index and Mortality in Postmenopausal Women

Concerns about reverse causality and selection bias complicate the interpretation of studies of body mass index (BMI, calculated as weight (kg)/height (m)2) and mortality in older adults. The objective of this study was to investigate methodological explanations for the apparent attenuation of obesity-related risks in older adults. We used data from 68,132 participants in the Women's Health Initiative (WHI) clinical trial for this analysis. All of the participants were postmenopausal women aged 50-79 years at baseline (1993-1998). To examine reverse causality and selective attrition, we compared rate ratios from inverse probability of treatment- and censoring-weighted Poisson marginal structural models with results from an unweighted adjusted Poisson regression model. The estimated mortality rate ratios and 95% confidence intervals for BMIs of 30.0-34.9, 35.0-39.9 and ≥40.0 were 0.86 (95% confidence interval (CI): 0.77, 0.96), 0.85 (95% CI: 0.72, 0.99), and 0.88 (95% CI: 0.72, 1.07), respectively, in the unweighted model. The corresponding mortality rate ratios were 0.96 (95% CI: 0.86, 1.07), 1.12 (95% CI: 0.97, 1.29), and 1.31 95% CI: (1.08, 1.57), respectively, in the marginal structural model. Results from the inverse probability of treatment- and censoring-weighted marginal structural model were attenuated in low BMI categories and increased in high BMI categories. The results demonstrate the importance of accounting for reverse causality and selective attrition in studies of older adults.

Associations of body weight and weight change with cardiovascular events and mortality in patients with coronary heart disease

BACKGROUND AND AIMS

It is recommended that patients with coronary heart disease (CHD) pursue a normal body weight, while the effects of body weight and weight change on prognosis are still controversial. The present study was to assess these effects using a large-scale population with CHD in China.

METHODS

A total of 5276 patients with CHD were included from Jan 2000 to Dec 2014. Baseline and endpoint weights were measured. Outcomes including mortality and cardiovascular events were obtained.

RESULTS

Relative to patients with normal weight, risks for adverse outcomes were lowest in overweight patients and similar in obese patients. Hazard ratios (HRs) and 95% confidence interval (95% CI) for all-cause death were 1.42 (1.06, 1.91) if overweight turned into normal weight and were 2.01 (1.28, 3.16) or 5.33 (2.81, 10.1) if obese turned into overweight or normal weight. Death risk increased with the extent of weight loss and moderate or large weight gain (p<0.05 for all). Similar results were found when risks for cardiovascular mortality and events were considered. Furthermore, these results remained significant when the patients were stratified by several covariates and even when several definitions of weight change were considered.

CONCLUSIONS

Obesity did not increase adverse outcome risks in patients with CHD. Both weight loss and weight gain increased adverse outcome risks regardless of baseline body weight. The findings suggest that maintaining a stable weight may be a better strategy for the reduction of risks for cardiovascular outcomes and all-cause death in patients with CHD.

Overweight or obese BMI is associated with earlier, but not later survival after common acute illnesses

Background

Obesity has been associated with improved short-term mortality following common acute illness, but its relationship with longer-term mortality is unknown.

Methods

Observational study of U.S. Health and Retirement Study (HRS) participants with federal health insurance (fee-for-service Medicare) coverage, hospitalized with congestive heart failure (N = 4287), pneumonia (N = 4182), or acute myocardial infarction (N = 2001), 1996–2012. Using cox proportional hazards models, we examined the association between overweight or obese BMI (BMI ≥ 25.0 kg/m²) and mortality to 5 years after hospital admission, adjusted for potential confounders measured at the same time as BMI, including age, race, sex, education, partnership status, income, wealth, and smoking status. Body mass index (BMI) was calculated from self-reported height and weight collected at the HRS survey prior to hospitalization (a median 1.1 year prior to hospitalization). The referent group was patients with a normal BMI (18.5 to < 25.0 kg/m²).

Results

Patients were a median of 79 years old (IQR 71–85 years). The majority of patients were overweight or obese: 60.3% hospitalized for heart failure, 51.5% for pneumonia, and 61.6% for acute myocardial infarction. Overweight or obese BMI was associated with lower mortality at 1 year after hospitalization for congestive heart failure, pneumonia, and acute myocardial infarction—with adjusted hazard ratios of 0.68 (95% CI 0.59–0.79), 0.74 (95% CI: 0.64–0.84), and 0.65 (95%CI: 0.53–0.80), respectively. Among participants who lived to one year, however, subsequent survival was similar between patients with normal versus overweight/obese BMI.

Conclusions

In older Americans, overweight or obese BMI was associated with improved survival following hospitalization for congestive heart failure, pneumonia, and acute myocardial infarction. This association, however, is limited to the shorter-term. Conditional on surviving to one year, we did not observe a survival advantage associated with excess weight.

Electronic supplementary material

The online version of this article (10.1186/s12877-018-0726-2) contains supplementary material, which is available to authorized users.

Prolonged Duration of Therapy Is Associated With Improved Survival in Patients Treated for Relapsed/Refractory Multiple Myeloma in Routine Clinical Care in the United States

BACKGROUND

In clinical trials, an extended therapy duration has been associated with better outcomes in patients with newly diagnosed multiple myeloma (NDMM). However, data on how the therapy duration affects the outcomes for patients with relapsed/refractory multiple myeloma (RRMM) are limited. We conducted a large, retrospective study in the United States to evaluate the effect of the duration of second-line therapy on overall survival.

PATIENTS AND METHODS

Adults with NDMM from January 2008 to June 2015 were followed up to identify their second-line therapy. The duration of therapy (DOT) and time to next therapy (TTNT), as a proxy for progression-free survival, were estimated using the Kaplan-Meier method. The relationship between the duration of second-line therapy and overall survival was evaluated with a logistic marginal structural model to mitigate the risk of treatment selection and survival bias.

RESULTS

A total of 628 NDMM patients developed a relapse after initial therapy. The median DOT for second-line therapy was 6.9 months (95% confidence interval [CI], 5.9-7.7 months), which was shorter than the corresponding TTNT (median, 15.1 months; 95% CI, 13.4-17.3 months). Each additional month of second-line therapy was associated with a reduced adjusted risk of death at 1 year (odds ratio, 0.78; 95% CI, 0.77-0.83; P < .001).

CONCLUSION

In a large database capturing a heterogeneous patient population and varied treatment patterns reflecting routine clinical care, we found a clinical benefit for continued longer DOT at first relapse. Despite the emerging paradigm favoring continuous therapy, second-line progression-free survival (utilizing TTNT as the proxy) was more than twofold longer than the DOT. Understanding the barriers to extended DOT could help to improve the outcomes for RRMM patients.

International Differences in the Risk of Death from Smoking and Obesity: The Case of the United States and Finland

Despite much interest in the health risks associated with behavioral factors, little is known about whether individuals residing in different countries experience a different set of risks. International comparisons of the death risks from major behavioral factors can shed light on whether features of health systems and epidemiological histories modify the health effects of risky behaviors. We used nationally representative samples and mortality linkages spanning the 1971-2014 period from the United States and Finland to examine cross-national differences in the risks of death from cigarette smoking and obesity. We evaluated both current and former smoking and current and prior obesity. In 1990, the approximate midpoint of our study, the death risks from current smoking were about 55% higher in U.S. women compared to Finnish women, but similar for men in the two countries. Death risks from smoking significantly increased over the period for women in both countries and there was no parallel increase in risks among men. Death risks from obesity did not significantly differ in the two countries and no significant trend in the risks were detected in either country. Reasons for the relatively high and increasing risks from smoking among American women warrant further evaluation.

Dynamics of biomarkers in relation to aging and mortality

Contemporary longitudinal studies collect repeated measurements of biomarkers allowing one to analyze their dynamics in relation to mortality, morbidity, or other health-related outcomes. Rich and diverse data collected in such studies provide opportunities to investigate how various socio-economic, demographic, behavioral and other variables can interact with biological and genetic factors to produce differential rates of aging in individuals. In this paper, we review some recent publications investigating dynamics of biomarkers in relation to mortality, which use single biomarkers as well as cumulative measures combining information from multiple biomarkers. We also discuss the analytical approach, the stochastic process models, which conceptualizes several aging-related mechanisms in the structure of the model and allows evaluating "hidden" characteristics of aging-related changes indirectly from available longitudinal data on biomarkers and follow-up on mortality or onset of diseases taking into account other relevant factors (both genetic and non-genetic). We also discuss an extension of the approach, which considers ranges of "optimal values" of biomarkers rather than a single optimal value as in the original model. We discuss practical applications of the approach to single biomarkers and cumulative measures highlighting that the potential of applications to cumulative measures is still largely underused.

BMI and all cause mortality: systematic review and non-linear dose-response meta-analysis of 230 cohort studies with 3.74 million deaths among 30.3 million participants

OBJECTIVE

To conduct a systematic review and meta-analysis of cohort studies of body mass index (BMI) and the risk of all cause mortality, and to clarify the shape and the nadir of the dose-response curve, and the influence on the results of confounding from smoking, weight loss associated with disease, and preclinical disease.

DATA SOURCES

PubMed and Embase databases searched up to 23 September 2015.

STUDY SELECTION

Cohort studies that reported adjusted risk estimates for at least three categories of BMI in relation to all cause mortality.

DATA SYNTHESIS

Summary relative risks were calculated with random effects models. Non-linear associations were explored with fractional polynomial models.

RESULTS

230 cohort studies (207 publications) were included. The analysis of never smokers included 53 cohort studies (44 risk estimates) with >738 144 deaths and >9 976 077 participants. The analysis of all participants included 228 cohort studies (198 risk estimates) with >3 744 722 deaths among 30 233 329 participants. The summary relative risk for a 5 unit increment in BMI was 1.18 (95% confidence interval 1.15 to 1.21; I(2)=95%, n=44) among never smokers, 1.21 (1.18 to 1.25; I(2)=93%, n=25) among healthy never smokers, 1.27 (1.21 to 1.33; I(2)=89%, n=11) among healthy never smokers with exclusion of early follow-up, and 1.05 (1.04 to 1.07; I(2)=97%, n=198) among all participants. There was a J shaped dose-response relation in never smokers (Pnon-linearity <0.001), and the lowest risk was observed at BMI 23-24 in never smokers, 22-23 in healthy never smokers, and 20-22 in studies of never smokers with ≥20 years' follow-up. In contrast there was a U shaped association between BMI and mortality in analyses with a greater potential for bias including all participants, current, former, or ever smokers, and in studies with a short duration of follow-up (<5 years or <10 years), or with moderate study quality scores.

CONCLUSION

Overweight and obesity is associated with increased risk of all cause mortality and the nadir of the curve was observed at BMI 23-24 among never smokers, 22-23 among healthy never smokers, and 20-22 with longer durations of follow-up. The increased risk of mortality observed in underweight people could at least partly be caused by residual confounding from prediagnostic disease. Lack of exclusion of ever smokers, people with prevalent and preclinical disease, and early follow-up could bias the results towards a more U shaped association.