Weight-Adjusted Waist Index and Mortality Among Older Adults: Findings from NHANES 1999–2018

Background The weight-adjusted waist index (WWI) is a new anthropometric measure that reflects central obesity in relation to body weight. Previous studies have examined the relationship between WWI and all-cause mortality in populations with hypertension; however, evidence specifically pertaining to the elderly remains lacking. This study aims to examine the relationship between WWI and all-cause as well as cardiovascular mortality in older adults. Methods We analyzed 16,242 adults aged ≥ 60 years from the 1999–2018 National Health and Nutrition Examination Survey (NHANES). WWI was calculated from baseline examination measurements of weight and waist circumference. The association between WWI and mortality outcomes was analyzed utilizing the Kaplan–Meier survival modeling, Cox regression analysis, smooth curve fitting analysis, threshold effect analysis, and subgroup analysis. Stratification factors for subgroups included demographics (age, sex, race/ethnicity, marital status, education, poverty-income ratio) and health factors (smoking, alcohol use, physical activity, hypertension, and diabetes). Results The mean age of participants was 70.39 ± 7.32 years, with a gender distribution of 49.87% male and 50.13% female. The mean WWI was 11.51 ± 0.74 cm/√kg. There were 5,779 all-cause deaths and 1,907 cardiovascular disease (CVD) deaths. Kaplan–Meier analysis indicated significant differences in all-cause and CVD mortality across WWI categories. After adjusting for covariates, WWI was positively associated with all-cause mortality (HR = 1.072, 95%CI: 1.03, 1.11, p = 0.0006) and CVD mortality (HR = 1.09, 95%CI :1.02, 1.17, p = 0.015).These associations remained significant after full adjustment. Threshold analysis revealed an inflection point for all-cause mortality at 11.24 cm/√kg, above this threshold, the risk significantly increased (HR = 1.14, 95% CI: 1.08–1.21, p < 0.0001). For CVD mortality, the inflection point was determined to be 12.74 cm/√kg. Conclusion Among older adults in the U.S., a higher WWI is associated with increased risks of all-cause and cardiovascular mortality. This relationship is non-linear, showing minimal risk variation at lower WWI values but a marked increase in mortality risk above approximately 11cm/√kg. WWI is a significant indicator of mortality, even after adjusting for various demographic, socioeconomic, lifestyle, and health factors.