Sex-specific associations of urinary zinc, iron, and zinc-to-iron ratio with obesity indicators and phenotypes.

BACKGROUND

Trace elements such as zinc (Zn) and iron (Fe) may influence obesity risk; however, the role of their balance, reflected by the urinary zinc-to-iron ratio (ZIR), remains unclear.

METHODS

We analyzed baseline data from 14,761 adults aged 30-79 years in the China Multi-Ethnic Cohort. Urinary zinc and iron concentrations were normalized using urinary specific gravity to account for variations in urine dilution.

RESULTS

Urinary Zn and the ZIR were positively associated with waist circumference and general obesity. Urinary Fe was linked to increased hip circumference (β = 0.196, 95% CI 0.077-0.316) but a lower risk of overweight (OR = 0.947, 95% CI 0.907-0.988). These associations were stronger among individuals with higher obesity indicators. Stratified analyses showed sex-specific patterns: in males, ZIR was associated with overweight and abdominal obesity, while in females, urinary Zn and ZIR were significantly related to general obesity risk. Urinary Fe showed inverse associations with overweight and abdominal obesity in males (OR = 0.87 and 0.89, respectively), but was positively associated with abdominal obesity in females (OR = 1.07, 95% CI 1.01-1.13).

CONCLUSION

Urinary Zn, Fe, and ZIR are associated with obesity indicators and phenotypes, with notable sex differences. ZIR may serve as a non-invasive biomarker of obesity risk. These findings suggest the potential for sex-specific nutritional strategies in obesity prevention and management.