Association between serum copper, zinc and their ratio and handgrip strength among adults: a study from National Health and Nutrition Examination Survey (NHANES) 2011-2014

Evidence for the association between serum copper and zinc status and handgrip strength is very limited only in several observational studies with study participants of specific population or a narrower age range. The aim of this study was to evaluate the association between serum copper, zinc and their ratio and handgrip strength in the general population. This study included adult participants aged 20-80 years with complete data of serum copper and zinc status and handgrip strength from NHANES 2011-2014. Handgrip strength was calculated as the average of the maximum measure obtained in each hand with a grip strength dynamometer and corrected using BMI. Serum copper and zinc levels were measured using inductively coupled plasma dynamic reaction cell mass spectrometry, and their ratios were calculated. The multivariable linear regression and restricted cubic spline models were used. Serum copper level was inversely associated with BMI-corrected handgrip strength, and the beta coefficients (95% confidence intervals) comparing the second, third, and fourth to the lowest quartiles of serum copper level were - 0.17 kg (- 0.26; - 0.08), - 0.22 kg (- 0.32; - 0.13), and - 0.36 kg (- 0.44; - 0.28), respectively (P for trend < 0.001). Non-linear association was detected between serum copper level and BMI-corrected handgrip strength (P < 0.01). Consistent with serum copper, serum copper/zinc ratio was inversely associated with BMI-corrected handgrip strength. However, no significant associations were observed between serum zinc level and BMI-corrected handgrip strength (all P > 0.05). Higher serum copper level and copper/zinc ratios were significantly associated with lower handgrip strength. Further research is needed to address related issues.