Shape of BMI-Mortality Risk Associations: Reverse Causality and Heterogeneity in a Representative Cohort of US Adults

Obesity paradox of cardiovascular mortality in older adults in the United States: A cohort study using 1997-2018 National Health Interview Survey data linked with the National Death Index

BACKGROUND

Large-scale, population-based investigations primarily investigating the association between body mass index (BMI) and cardiovascular disease (CVD) mortality among older and younger adults in the United States (U.S.) are lacking.

OBJECTIVE

To evaluate the relationship between BMI and CVD mortality in older (≥65 years) and younger (<65 years) adults and to identify the nadir for CVD mortality.

DESIGN

This cohort study used serial cross-sectional data from the 1997 to 2018 National Health Interview Survey (NHIS) linked with the National Death Index. NHIS is an annual nationally representative household interview survey of the civilian noninstitutionalized U.S.

POPULATION

SETTING

Residential units of the civilian noninstitutionalized population in the U.S.

PARTICIPANTS

The target population for the NHIS is the civilian noninstitutionalized U.S. population at the time of the interview. We included all adults who had BMI data collected at 18 years and older and with mortality data being available. To minimize the risk of reverse causality, we excluded adults whose survival time was ≤2 years of follow-up after their initial BMI was recorded and those with prevalent cancer and/or CVD at baseline.

METHODS

We used the BMI record obtained in the year of the NHIS survey. Total CVD mortality used the NHIS data linked to the latest National Death Index data from the survey inception to December 31, 2019. We performed multivariable Cox proportional hazards regression models to estimate adjusted hazard ratios (aHRs) and 95 % confidence intervals (CIs).

RESULTS

The study included 425,394 adults; the mean (SD) age was 44 (16.7) years. During a median follow-up period of 11 years, 12,089 CVD-related deaths occurred. In older adults, having overweight was associated with a lower risk of CVD mortality (aHR 0.92 [95 % CI, 0.87-0.97]); having class I obesity (1.04 [0.97-1.12]) and class II obesity (1.12 [1.00-1.26]) was not significantly associated with an increased CVD mortality; and having class III obesity was associated with an increased risk of CVD mortality (1.63 [1.35-1.98]), in comparison with adults who had a normal BMI. Yet, in younger adults, having overweight, class I, II, and III obesity was associated with a progressively higher risk of CVD mortality. The nadir for CVD mortality is 28.2 kg/m2 in older adults and 23.6 kg/m2 in younger adults.

CONCLUSION

This U.S. population-based cohort study highlights the significance of considering age as a crucial factor when providing recommendations and delivering self-care educational initiatives for weight loss to reduce CVD mortality.

Body mass index, waist circumference, and mortality in subjects older than 80 years: a Mendelian randomization study

BACKGROUND AND AIMS

Emerging evidence has raised an obesity paradox in observational studies of body mass index (BMI) and health among the oldest-old (aged ≥80 years), as an inverse relationship of BMI with mortality was reported. This study was to investigate the causal associations of BMI, waist circumference (WC), or both with mortality in the oldest-old people in China.

METHODS

A total of 5306 community-based oldest-old (mean age 90.6 years) were enrolled in the Chinese Longitudinal Healthy Longevity Survey (CLHLS) between 1998 and 2018. Genetic risk scores were constructed from 58 single-nucleotide polymorphisms (SNPs) associated with BMI and 49 SNPs associated with WC to subsequently derive causal estimates for Mendelian randomization (MR) models. One-sample linear MR along with non-linear MR analyses were performed to explore the associations of genetically predicted BMI, WC, and their joint effect with all-cause mortality, cardiovascular disease (CVD) mortality, and non-CVD mortality.

RESULTS

During 24 337 person-years of follow-up, 3766 deaths were documented. In observational analyses, higher BMI and WC were both associated with decreased mortality risk [hazard ratio (HR) 0.963, 95% confidence interval (CI) 0.955-0.971 for a 1-kg/m2 increment of BMI and HR 0.971 (95% CI 0.950-0.993) for each 5 cm increase of WC]. Linear MR models indicated that each 1 kg/m2 increase in genetically predicted BMI was monotonically associated with a 4.5% decrease in all-cause mortality risk [HR 0.955 (95% CI 0.928-0.983)]. Non-linear curves showed the lowest mortality risk at the BMI of around 28.0 kg/m2, suggesting that optimal BMI for the oldest-old may be around overweight or mild obesity. Positive monotonic causal associations were observed between WC and all-cause mortality [HR 1.108 (95% CI 1.036-1.185) per 5 cm increase], CVD mortality [HR 1.193 (95% CI 1.064-1.337)], and non-CVD mortality [HR 1.110 (95% CI 1.016-1.212)]. The joint effect analyses indicated that the lowest risk was observed among those with higher BMI and lower WC.

CONCLUSIONS

Among the oldest-old, opposite causal associations of BMI and WC with mortality were observed, and a body figure with higher BMI and lower WC could substantially decrease the mortality risk. Guidelines for the weight management should be cautiously designed and implemented among the oldest-old people, considering distinct roles of BMI and WC.

Associations Between Mid- to Late-Life Body Mass Index and Chronic Disease-Free Survival: A Nationwide Twin Study

BACKGROUND

Some studies have linked late-life overweight to a reduced mortality risk compared to normal body mass index (BMI). However, the impact of late-life overweight and its combination with mid-life BMI status on healthy survival remains unclear. We aimed to investigate whether and to what extent mid- and/or late-life overweight are associated with chronic disease-free survival.

METHODS

Within the Swedish Twin Registry, 11 597 chronic disease-free twins aged 60-79 years at baseline were followed up for 18 years. BMI (kg/m2) was recorded at baseline and 25-35 years before baseline (ie, midlife) and divided as underweight (<20), normal (≥20-25), overweight (≥25-30), and obese (≥30). Incident chronic diseases (cardiovascular diseases, type 2 diabetes, and cancer) and deaths were ascertained via registries. Chronic disease-free survival was defined as years lived until the occurrence of any chronic diseases or death. Data were analyzed using multistate survival analysis.

RESULTS

Of all participants, 5 640 (48.6%) were overweight/obese at baseline. During the follow-up, 8 772 (75.6%) participants developed at least 1 chronic disease or died. Compared to normal BMI, late-life overweight and obesity were associated with 1.1 (95% CI, 0.3, 2.0) and 2.6 (1.6, 3.5) years shorter chronic disease-free survival. Compared to normal BMI through mid- to late life, consistent overweight/obesity and overweight/obesity only in mid-life led to 2.2 (1.0, 3.4) and 2.6 (0.7, 4.4) years shorter disease-free survival, respectively.

CONCLUSIONS

Late-life overweight and obesity may shorten disease-free survival. Further research is needed to determine whether preventing overweight/obesity from mid- to late life might favor longer and healthier survival.

Age-Dependent Association Between Body Mass Index and All-Cause Mortality Among Patients with Hypertension: A Longitudinal Population-Based Cohort Study in China

PURPOSE

The association between body mass index (BMI) and all-cause mortality may vary among hypertensive patients of different ages. This study aimed to investigate the age-dependent association between BMI and all-cause mortality among patients with hypertension.

PATIENTS AND METHODS

A total of 212,394 participants with hypertension aged 20-85 years from Minhang Hypertension Standardization Management System in Shanghai of China were included. Follow-up began at the time when individuals were first recorded and ended at death, loss to follow-up, or December 31, 2018, whichever came first. Additive Cox proportional hazards models with thin plate smoothing functions and conventional Cox proportional hazards models were adopted to examine the relationship between BMI, age, and mortality. The joint effect of BMI and age on mortality was assessed using a bivariate response model.

RESULTS

We found that the BMI-mortality relationship followed a U-shaped pattern, with a trough at 26-27 kg/m2. Compared with normal weight, underweight was associated with a 50% increased risk of premature mortality (hazard ratio 1.50, 95% confidence interval 1.43 to 1.57). Whereas among those aged 45-59 and 60-85 years, overweight was associated with 13% (0.87, 0.80 to 0.94) and 18% (0.82, 0.80 to 0.84) reduction in risk of death, respectively. Bivariate response model indicated a significant interaction between BMI and age (P < 0.05). Among younger and older patients, we found a descending trend for mortality risk, with BMI increasing at different age levels, whereas a reverse J-shaped relation pattern was observed among middle-aged patients.

CONCLUSION

The impact of BMI on all-cause mortality in hypertensive patients varies with age, and moderate weight gain may benefit longevity in middle-aged and older patients.

Body mass index and all-cause mortality in a 21st century U.S. population: A National Health Interview Survey analysis

INTRODUCTION

Much of the data on BMI-mortality associations stem from 20th century U.S. cohorts. The purpose of this study was to determine the association between BMI and mortality in a contemporary, nationally representative, 21st century, U.S. adult population.

METHODS

This was a retrospective cohort study of U.S. adults from the 1999-2018 National Health Interview Study (NHIS), linked to the National Death Index (NDI) through December 31st, 2019. BMI was calculated using self-reported height & weight and categorized into 9 groups. We estimated risk of all-cause mortality using multivariable Cox proportional hazards regression, adjusting for covariates, accounting for the survey design, and performing subgroup analyses to reduce analytic bias.

RESULTS

The study sample included 554,332 adults (mean age 46 years [SD 15], 50% female, 69% non-Hispanic White). Over a median follow-up of 9 years (IQR 5-14) and maximum follow-up of 20 years, there were 75,807 deaths. The risk of all-cause mortality was similar across a wide range of BMI categories: compared to BMI of 22.5-24.9 kg/m2, the adjusted HR was 0.95 [95% CI 0.92, 0.98] for BMI of 25.0-27.4 and 0.93 [0.90, 0.96] for BMI of 27.5-29.9. These results persisted after restriction to healthy never-smokers and exclusion of subjects who died within the first two years of follow-up. A 21-108% increased mortality risk was seen for BMI ≥30. Older adults showed no significant increase in mortality between BMI of 22.5 and 34.9, while in younger adults this lack of increase was limited to the BMI range of 22.5 to 27.4.

CONCLUSION

The risk of all-cause mortality was elevated by 21-108% among participants with BMI ≥30. BMI may not necessarily increase mortality independently of other risk factors in adults, especially older adults, with overweight BMI. Further studies incorporating weight history, body composition, and morbidity outcomes are needed to fully characterize BMI-mortality associations.

Body Mass Index and Cognition: Associations Across Mid- to Late Life and Gender Differences

BACKGROUND

Higher mid-life body mass index (BMI) is associated with lower late-life cognition. Associations between later-life BMI and cognition are less consistent; evidence suggests reverse causation may play a role. We aimed to characterize associations between BMI and cognition across a wide age range during mid- to late life (55-85 years) and examine whether associations vary by gender.

METHODS

We used data from the Health and Retirement Study (HRS) (N = 39,153) to examine the association between BMI and 3 cognitive outcomes: cognitive level, cognitive decline, and cognitive impairment. We used a series of linear regression, mixed effects regression, and logistic regression models, adjusting for potential confounders.

RESULTS

Higher BMI before age 65 (midlife) was associated with lower cognitive performance, faster rates of cognitive decline, and higher odds of cognitive impairment in late life. Averaging across analyses assessing associations between BMI measured before age 60 and late-life cognition, a 5-unit higher level of BMI was associated with a 0.26 point lower cognitive score. Beyond age 65, associations flipped, and higher BMI was associated with better late-life cognitive outcomes. Associations in both directions were stronger in women. Excluding those with BMI loss attenuated findings among women in older ages, supporting the reverse causation hypothesis.

CONCLUSIONS

In this sample, age 65 represented a critical turning point between mid- and late life for the association between BMI and cognition, which has important implications for recruitment strategies for studies focused on risk factors for late-life cognitive outcomes. Evidence of gender differences raises the need to further investigate plausible mechanisms.

Depressive symptoms and mortality - effect variation by body mass index: a prospective study in a primary care population

BACKGROUND/OBJECTIVE

Pre-existing diseases have been found to affect the relationship between body mass index (BMI) and mortality. However, psychiatric disorders common in general population have not been previously addressed. The aim of this study was to assess the relationship of depressive symptoms and BMI with all-cause mortality.

METHODS

A prospective cohort study in Finnish primary care setting was conducted. A population survey identified 3072 middle-aged subjects who had elevated cardiovascular risk. Subjects who attended clinical examination and completed Beck's Depression Inventory (BDI) (n = 2509) were included in this analysis. Effect of depressive symptoms and BMI on all-cause mortality after 14 years follow-up was estimated in models adjusted for age, sex, education years, current smoking, alcohol use, physical activity, total cholesterol, systolic blood pressure, and glucose disorders.

RESULTS

When subjects with and without increased depressive symptoms were compared, the fully adjusted hazard ratios (HR) for all-cause mortality in the BMI categories (<25.0, 25.0-29.9, 30.0-34.9, ≥35.0 kg/m²) were 3.26 (95% CI 1.83 to 5.82), 1.31 (95% CI 0.83 to 2.06), 1.27 (95% CI 0.76 to 2.11), and 1.25 (95% CI 0.63 to 2.48), respectively. The lowest risk of death was among non-depressive subjects who had BMI < 25.0 kg/m².

CONCLUSIONS

Effect of increased depressive symptoms on all-cause mortality risk seems to vary with BMI. Elevated mortality risk is especially apparent among depressive subjects with normal weight. Among individuals with overweight and obesity, increased depressive symptoms seem not to further increase all-cause mortality.

Body mass index and 12-year mortality among older Mexican Americans aged 75 years and older

Background

The role of obesity in mortality in the very old and old-oldest Hispanic population has not been studied. The objective of this study was to examine the effect of body mass index (BMI) on 12-year mortality among older Mexican Americans aged 75 years and older.

Methods

Twelve year prospective cohort study consisting of a population-based sample of 1415 non-institutionalized Mexican American men and women aged 75 and older from 5 southwestern states: Arizona, California, Colorado, New Mexico, and Texas. Data was from Wave 5 of the Hispanic Established Population for the Epidemiologic Study of the Elderly (2004/2005–2016). Socio-demographics, body mass index (BMI), self-reported medical conditions, disability, depressive symptoms, falls, Mini-Mental-State-Examination (MMSE), and Short Physical Performance Battery (SPPB) were assessed at baseline during 2004–2005. BMI (Kg/m²) was classified as underweight (< 18.5), normal weight (18.5 to < 25), overweight (25 to < 30), obesity category I (30 to < 35), and obesity category II/morbid obesity (≥ 35). For assessment of mortality, deaths were ascertained through the National Death Index and report from relatives. Cox proportional hazards regression analysis was performed to estimate the hazard ratio (HR) of 12-year mortality as a function of BMI categories at baseline.

Results

The mean BMI was 27.5 ± 1.7 with participants classified as 1.8% underweight, 30.8% normal weight, 39.2% overweight, 20.7% obesity category I, and 7.6% obesity category II/morbid obesity. Mexican Americans aged ≥75 years with overweight or obesity category I had a reduced HR of death (0.82, 95% CI = 0.70–0.96 and 0.75, 95% CI = 0.62–0.91, respectively) over 12-years of follow-up. The HR of death for underweight and obesity category II/morbid obesity participants was 1.59 (95% CI = 1.03–2.45) and 1.12 (95% CI = 0.85–1.46), respectively. Female participants and those with high scores in the MMSE and SPPB had decreased risk of death.

Conclusions

This study showed the protective effect of overweight and obesity on mortality in Mexican Americans above 75 years of age, which might have implications when treating older adults with overweight and obesity.

Effects of weight change on all causes, digestive system and other causes mortality in Southern Italy: a competing risk approach

Weight change is associated with all causes of death, cardiovascular, and cancer mortality and a heterogeneous group of other causes of death. We aimed to estimate the effect of weight change on all causes and cause-specific mortality in a cohort with a high prevalence of deaths due to diseases of the digestive system.MethodsIn this prospective cohort study, 2230 subjects aged 30 to 50 years were examined. The study consisted of a 32-year longitudinal study period (January 1985 to December 2017) and mortality follow-up. Outcomes were mortality from all causes and deaths from gastrointestinal disease. Root Mean Squared Error (RMSE) was evaluated to capture individual residual variation in Body Mass Index (BMI) after adjustment for baseline BMI, and the relationship of residual variation with mortality was calculated as cumulative incidence function and cause-specific hazard (CSH) rate.ResultsIn total, 793 participants died during the follow-up, 96 of them due to Digestive system causes. Magnitude of residual variation weight in the last quintile was associated with all-cause mortality (relative risk, 2.00; 95% CI, 1.54-2.59) and Digestive system causes (relative risk, 3.82; 95% CI, 1.86-7.81).ConclusionThe findings suggest an association between weight change and gastrointestinal disease mortality. Epidemiological works studying the correlation between weight change and mortality should consider this aspect.