Examining the Longitudinal Association of Weight-Adjusted Waist Index With Risk of Arthritis, All-Cause Mortality, and COVID-19 Pandemic Related Effect on WWI: Evidence From Health and Retirement Study

The weight-adjusted waist index (WWI), calculated as waist circumference
(cm)/√weight (kg) is positively associated with arthritis and all-cause mortality. However,
its longitudinal association with arthritis and all-cause mortality among older population,
where excess abdominal fat plays a key role in disease development and death, remains
underexplored. Thus, the aim of this dissertation was to investigate the longitudinal
association between WWI and the risk of arthritis and mortality among U.S aging
population.
We analyzed data from 3,765 participants aged 51+ in the Health and Retirement
Study (2006–2022). Group-based trajectory modeling was used to create WWI
trajectories. The relationship between WWI trajectories and arthritis risk was assessed
using weighted logistic regression, while the effect of WWI on mortality was evaluated
using weighted Cox regression. The pandemic's effect on WWI was analyzed using linear
mixed-effects regression. We reported odds ratios (ORs), hazard ratios (HRs), mean
difference, 95% CIs, and P-values.
Three distinct WWI trajectories were identified: low (30.0%), intermediate
(59.4%), and high (10.6%). Over 12 years, the incidence of arthritis was 57.7%.
Subgroup analysis showed that alcohol drinkers in the high-WWI trajectory [AOR =
1.87; 95% CI: 1.21, 2.88] had a higher risk of arthritis compared to the low-WWI
trajectory. Similarly, among those engaging in high physical activity, the high-WWI
trajectory had a higher risk of arthritis [AOR = 3.85; 95% CI: 1.63, 9.13]. The overall
incidence of death was 95 deaths per 1000 person-years. For each 1 cm/√kg increase in
WWI, the risk of death increased by 9% [AHR = 1.09; 95% CI: 1.04, 1.14]. This association was significant in men [AHR = 1.16; 95% CI: 1.05, 1.29], but not in women
[AHR = 1.06; 95% CI: 0.99, 1.12]. Finally, WWI increased from pre- to post-pandemic
[β = 0.18; 95% CI: 0.10, 0.27].
We identified three distinct WWI trajectories: low, intermediate and high.
Individuals in the high-WWI trajectory who consumed alcohol or engaged in high
physical activity levels had a greater risk of arthritis than those in the low-WWI
trajectory. WWI was positively associated with mortality risk. Gender modified the effect
of WWI on mortality. Abdominal obesity increased during COVID-19 pandemic.