The threshold effect of a body shape index on phenotypic age acceleration in U.S. adults: Insights from NHANES 1999 to 2010

Nov 15, 2025Medicine

Body shape index linked to faster aging in U.S. adults

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Abstract

A total of 23,045 participants showed a positive correlation between body shape index () and (PhenoAgeAccel) with a regression coefficient of 1.05.

ABSI is calculated as waist circumference divided by the square of height and the two-thirds power of body mass index.
An L-shaped relationship was found between ABSI and PhenoAgeAccel, indicating that ABSI is only significantly associated with accelerated aging above an inflection point of 7.97.
For participants with ABSI above 7.97, the correlation with PhenoAgeAccel was stronger, with a regression coefficient of 2.63.
The association between ABSI and PhenoAgeAccel was more significant in younger individuals (aged 20 to 39 years) than in those aged 40 years and older.
Men exhibited a stronger association between ABSI and PhenoAgeAccel compared to women.
Individuals without hypertension or diabetes showed a more pronounced association between ABSI and PhenoAgeAccel than those with these conditions.

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This study examines the relationship between (ABSI) and accelerated aging in a nationally representative U.S. population. Data from the 1999 to 2010 National Health and Nutrition Examination Survey were analyzed. ABSI numerically equals to waist circumference divided by the square of height and two-thirds power of body mass index. Phenotypic age (PhenoAge) is a biological age estimation based on a combination of clinical markers, while (PhenoAgeAccel) is calculated as the difference between 1's PhenoAge and chronological age. Multivariable linear regression models were used to assess the association between ABSI and PhenoAgeAccel. Smoothed curve fitting and threshold effect analysis were performed to explore the nonlinear relationship between these variables. Subgroup analyses were conducted to evaluate the consistency of the association across different demographic and clinical strata. A total of 23,045 participants were included, with a mean age of 49.15 years and 49.1% male representation. After adjusting for multiple covariates, the multivariable linear regression model showed a positive correlation between ABSI and PhenoAgeAccel (β: 1.05, 95% CI: 0.77-1.34). An L-shaped relationship was observed between ABSI and PhenoAgeAccel (P for nonlinearity < .001), with an inflection point at 7.97. Below this inflection point, no significant association was observed, while above it, ABSI was positively associated with PhenoAgeAccel (β: 2.63, 95% CI: 2.28-2.97, P < .001). Subgroup analyses indicated that the association between ABSI and PhenoAgeAccel was more pronounced in individuals aged 20 to 39 years compared with those aged ≥ 40 years, in men compared with women, and in those without hypertension or diabetes compared with those with these conditions. This study demonstrates a positive L-shaped correlation between ABSI and PhenoAgeAccel in U.S. adults.

Key numbers

1.05

Increase in per unit

Adjusted for multiple covariates in the analysis.

7.97

Inflection point for

Identified through threshold effect analysis.

2.63

Increase in above inflection point

β coefficient in the adjusted model for ≥ 7.97.

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The threshold effect of a body shape index on phenotypic age acceleration in U.S. adults: Insights from NHANES 1999 to 2010

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