Association between serum uric acid concentrations and grip strength: Is there effect modification by age?

Background: Given that some of the deleterious effects of uric acid (UA) on health are greater in younger than in older subjects, and that age is strongly associated with skeletal muscle composition and function, this study tested the hypothesis that the association between UA and muscle strength differs by age.

Methods: Cross-sectional analysis with 3595 individuals who participated in NHANES 2011-2012. Serum uric acid was determined by the uricase-peroxidase technique. Grip strength was calculated as the average of the best measure obtained in each hand with a Takei digital grip strength dynamometer. Linear regression models were adjusted for the main confounders.

Results: In individuals aged 20-40 years, the beta coefficients (95% CI) of muscle strength as dependent variable and UA as independent variable comparing the second and third to the lowest tertile of UA were -0.45 kg (-1.46; 0.57) and -2.36 kg (-3.27; -1.44), respectively, p-linear trend ≤0.01. By contrast, in subjects aged 40-60 years the corresponding beta coefficients were 0.21 kg (-1.00; 1.42) and -0.45 kg (-2.10; 1.20), p-linear trend: 0.60; and for subjects ≥60 years they were 0.58 kg (-3.27; 1.65) and 1.57 kg (0.63; 2.50), p-linear trend <0.01. These results held after numerous sensitivity analyses.

Conclusion: The association between UA and muscle strength differed depending on age: while a negative link was observed in adults aged 20-40 years, this relationship disappeared later in life, and was reversed after the age of 60. Future research should evaluate if uric acid targets for individuals with hyperuricemia should consider patients age and muscle strength.