Urinary nitrate is positively associated with muscle strength in older adults, but not in younger and middle-aged adults: NHANES 2011–2012

BACKGROUND: Few studies have evaluated the association between dietary nitrate (NO₃⁻) intake and muscle strength, and none has examined this relationship using urinary nitrate as a biomarker of nitrate intake. AIM: To investigate the association between urinary NO₃⁻ levels (a marker of NO₃⁻ consumption) and muscle strength in younger and middle-aged adults and older adults. METHODS: This cross-sectional study utilized data from the National Health and Nutrition Examination Survey (NHANES 2011-2012). A total of 1,301 individuals were included and stratified by age (< 60 years, n = 902; ≥60 years, n = 399). NO₃⁻ levels (ng/mL) in the urine were measured using ion chromatography coupled with tandem mass spectrometry and electrospray ionization. Muscle strength was assessed using combined handgrip strength (HGS), calculated as the sum of measurements from both hands. Linear regression analyses were performed to examine the association between urinary NO₃⁻ levels and HGS, adjusting for potential confounding variables. RESULTS: A positive association between urinary NO₃⁻ levels and HGS was observed in older adults (β = 0.00004; 95% CI: 0.00001-0.00007; p = 0.009). When urinary nitrate was normalized to urine osmolality, a positive association with HGS was also observed in older adults (β = 0.017; 95% CI: 0.0004-0.034; p = 0.046). No significant associations were found in the overall sample or among younger and middle-aged adults. CONCLUSION: Urinary NO₃⁻ levels were positively associated with handgrip strength in older adults, but not in younger and middle-aged adults. Given the small magnitude of this association, longitudinal studies are warranted to determine its clinical relevance.