How does obesity affect mortality through blood pressure and blood glucose in Chinese and US citizens? Insights from a causal mediation analysis of two large cohorts.

Background: Obesity, which has reached the scale of a global pandemic, is a leading cause of premature death. It is unclear to what extent its effect on mortality was driven by blood pressure or glucose levels in people of different ethnicities. Methods: We conducted a causal mediation analysis to estimate the mediation effect of blood pressure and glucose between body mass index (BMI) or waist-hip ratio (WHR) on mortality based on data from the China Kadoorie Biobank (CKB) (n = 458 385) and US National Health and Nutrition Examination Survey (NHANES) (1999-2008, n = 20 726). Results: The WHR's effect on mortality was mediated by blood pressure and glucose in the CKB data set by 38.7% (95% confidence interval (CI) = 34.1, 43.2) and 36.4% (95% CI = 31.6, 42.8), whereas in NHANES by 6.0% (95% CI = 2.3, 8.3) and 11.2% (95% CI = 4.7, 22.7), respectively. For associations between BMI and mortality in subjects with overweight or obesity, the mediator proportion of blood glucose and pressure was 49.4% (95% CI = 40.1, 62.5) and 16.9% (95% CI = 13.6, 22.9) in CKB and 9.10% (95% CI = 2.2, 25.9) and 16.7% (95% CI = 7.3, 49.0) in NHANES, respectively. We stratified the patients by their blood glucose, blood pressure level, or both into four groups. The effect of WHR on mortality was comparable across subgroups in either cohort. The associations between BMI and mortality were stronger in patients with higher blood pressure in CKB (P = 0.011) and blood glucose in NHANES (P = 0.035) in patients with overweight and obesity. Conclusions: The relationship between WHR and mortality in the CKB data set was potentially caused by blood pressure and glucose to a much greater extent than in the NHANES one. The effect of BMI influenced by blood pressure was significantly higher among Chinese individuals with overweight and obesity. These results implicate a different intervention strategy is required for blood pressure and blood glucose in China and US to prevent obesity and obesity-related premature death.

The relationship between body size and mortality in the linked Scottish Health Surveys: cross-sectional surveys with follow-up.

OBJECTIVE: To investigate the relationship between body mass index (BMI), waist circumference (WC) or waist-hip ratio (WHR) and all-cause mortality or cause-specific mortality. DESIGN: Cross-sectional surveys linked to hospital admissions and death records. SUBJECTS: In total, 20,117 adults (aged 18-86 years) from a nationally representative sample of the Scottish population. MEASUREMENTS: Cox proportional hazards models were used to estimate hazard ratios (HRs) for all-cause, or cause-specific, mortality. The three anthropometric measurements BMI, WC and WHR were the main variables of interest. The following were adjustment variables: age, gender, smoking status, alcohol consumption, survey year, social class and area of deprivation. RESULTS: BMI-defined obesity (≥ 30 kg m(-2)) was not associated with increased risk of mortality (HR = 0.93; 95% confidence interval = 0.80-1.08), whereas the overweight category (25-<30 kg m(-2)) was associated with a decreased risk (0.80; 0.70-0.91). In contrast, the HR for a high WC (men ≥ 102 cm, women ≥ 88 cm) was 1.17 (1.02-1.34) and a high WHR (men ≥ 1, women ≥ 0.85) was 1.34 (1.16-1.55). There was an increased risk of cardiovascular disease (CVD) mortality associated with BMI-defined obesity, a high WC and a high WHR categories; the HR estimates for these were 1.36 (1.05-1.77), 1.41 (1.11-1.79) and 1.44 (1.12-1.85), respectively. A low BMI (<18.5 kg m(-2)) was associated with elevated HR for all-cause mortality (2.66; 1.97-3.60), for chronic respiratory disease mortality (3.17; 1.39-7.21) and for acute respiratory disease mortality (11.68; 5.01-27.21). This pattern was repeated for WC but not for WHR. CONCLUSIONS: It might be prudent not to use BMI as the sole measure to summarize body size. The alternatives WC and WHR may more clearly define the health risks associated with excess body fat accumulation. The lack of association between elevated BMI and mortality may reflect the secular decline in CVD mortality.

Waist circumference and waist/hip ratio in relation to all-cause mortality, cancer and sleep apnea.

Abdominal obesity assessed by waist or waist/hip ratio are both related to increased risk of all-cause mortality throughout the range of body mass index (BMI). The relative risks (RRs) seem to be relatively stronger in younger than in older adults and in those with relatively low BMI compared with those with high BMI. Absolute risks and risk differences are preferable measures of risk in a public health context but these are rarely presented. There is a great lack of studies in ethnic groups (groups of African and Asian descent particularly). Current cut-points as recommended by the World Health Organization seem appropriate, although it may be that BMI-specific and ethnic-specific waist cut-points may be warranted. Waist alone could replace both waist-hip ratio and BMI as a single risk factor for all-cause mortality. There is much less evidence for waist to replace BMI for cancer risk mainly because of the relative lack of prospective cohort studies on waist and cancer risk. Obesity is also a risk factor for sleep apnoea where neck circumference seems to give the strongest association, and waist-hip ratio is a risk factor especially in severe obstructive sleep apnoea syndrome. The waist circumference and waist-hip ratio seem to be better indicators of all-cause mortality than BMI.

Reduction in allostatic load in older adults is associated with lower all-cause mortality risk: MacArthur studies of successful aging.

OBJECTIVES: To study the association between change in allostatic load (a risk score constructed from multiple biological markers) over a 2.5-year period and mortality in the following 4.5 years in older adults. METHODS: We measured 10 physiologic parameters at baseline (1988) in a cohort of 171 high-functioning, community-dwelling, 70- to 79-year-old adults. These measurements were repeated 2.5 years later, in 1991. Summary allostatic load scores for 1988 and 1991 were created as the weighted sum of the 10 biological markers and their second-order terms. Mortality status (alive or dead) for participants was determined 4.5 years later, in 1995. The association between change in allostatic load score (1988-1991) and subsequent mortality (1991-1995) was studied using logistic regression. RESULTS: Compared with participants whose allostatic load score decreased between 1988 and 1991, individuals whose allostatic load score increased had higher risk of all-cause mortality between 1991 and 1995 (15% versus 5%, p = .047). Adjusted for age and baseline allostatic load, each unit increment in the allostatic load change score was associated with mortality odds ratio of 3.3 (95% confidence interval, 1.1-9.8). CONCLUSION: Our results suggest that even in older ages, change in risk scores can be followed to improve assessment of mortality risk.

[Relationship between body mass index, waist circumference, and waist-to-hip ratio and mortality in elderly women: a 5-year follow-up study]. / Relação do índice de massa corporal, da relação cintura-quadril e da circunferência abdominal com a mortalidade em mulheres idosas: seguimento de 5 anos.

This study examines the association between body mass index (BMI), waist-to-hip ratio (WHR), and waist circumference (WC) and all-cause and cardiovascular mortality in elderly women in a 5-year longitudinal study of 575 female outpatients 60 years and over. The highest BMI, WHR, and WC quartiles and predefined BMI categories were analyzed as predictive variables. Death occurred in 88 (15.4%). Underweight (BMI < 18.5 kg/m2) was associated with all-cause mortality in uni- and multivariate analyses, regardless of age bracket. The survival curves and univariate analysis showed that the highest WHR quartile (> or = 0.97) was associated with all-cause mortality. However, after adjustment for age, smoking, and previous cardiovascular diseases, the increase in WHR was positively associated only in women from 60 to 80 years of age. None of the anthropometric measurements was associated with cardiovascular mortality. The results indicate that underweight and increased waist-to-hip ratio were predictors of all-cause mortality in elderly women, mainly among those under 80 years.

Enlarged waist combined with elevated triglycerides is a strong predictor of accelerated atherogenesis and related cardiovascular mortality in postmenopausal women.

BACKGROUND: Upward trends of obesity urge more effective identification of those at cardiovascular risk. A simple dichotomous indicator, enlarged waist (> or =88 cm) combined with elevated triglycerides (> or =1.45 mmol/L) (EWET), was shown to offer advantages in identifying individuals with atherogenic "lipid overaccumulation" compared with other indicators, including the metabolic syndrome defined by the National Cholesterol Education Program (MS-NCEP). Whether EWET offers superior disease and event prediction in postmenopausal women, however, remains unknown. METHODS AND RESULTS: A community-based sample of 557 women (48 to 76 years of age) were followed up for 8.5+/-0.3 years to assess the utility of EWET and MS-NCEP in estimating the risk of all-cause and cardiovascular mortality and the annual progression rate of aortic calcification. At baseline, 15.8% of women had EWET and 17.6% had MS-NCEP. All-cause mortality and cardiovascular mortality were increased in carriers of the dichotomous indicators (P<0.001). After adjustment for age, smoking, and LDL cholesterol, presence of EWET was associated with a 4.7-fold (95% CI, 2.2 to 9.8; P<0.001) increased risk and presence of MS-NCEP was associated with a 3.2-fold (95% CI, 1.5 to 6.5; P<0.001) increased risk for fatal cardiovascular events. Exclusion of women with prevalent diabetes did not change these trends; respective hazard ratios were 4.2 (95% CI, 1.9 to 9.3; P<0.001) and 2.5 (95% CI, 1.1 to 5.5; P<0.05). Among those who were discordant for EWET and MS-NCEP at baseline, those who had EWET alone (n=21) had a higher annual progression rate of aortic calcification compared with those who had MS-NCEP alone (n=31; P<0.05). CONCLUSIONS: The combined presence of EWET may be the best indicator of cardiovascular risk in postmenopausal women. Other components of the MS-NCEP add little medical value to screening in general practices.