Nonlinearity association of serum calcium with the risk of anaemia in US adults.

BACKGROUND: Calcium plays a key role in many bio-homeostasis functions. Previous studies indicated that serum calcium is associated with diseases such as anaemia. However, the evidence on the association between serum calcium levels and anaemia risk is limited. Thus, the purpose of our study is to investigate the relationship between serum calcium and anaemia in US adults. METHODS: This cross-sectional study used data from the National Health and Nutrition Examination Survey (NHANES) including 15,519 participants, aged ≥18 years. The analyses were performed using multivariate logistic regression and a generalized additive model (GAM). Subgroup analysis, stratified by gender and age, was also performed. RESULTS: Among the sample of 15,519 individuals, 1565 (10.8%) had been diagnosed with anaemia. Both the univariate logistic regression model and multivariate logistic regression model showed a reverse relationship between serum calcium and anaemia risk. Moreover, a non-linear association between serum calcium and anaemia risk was observed using GAM and smooth curve fitting. The inflection point of serum calcium was at 2.3 mmol/L. GAM with penalized splines suggested a reverse association between serum calcium and the prevalence of anaemia when the concentration of serum calcium was below 2.3 mmol/L. In contrast, we found no statistically significant difference when serum calcium concentration was higher than the inflection point (2.3 mmol/L). CONCLUSION: Lower serum calcium levels were associated with increased risk of anaemia risk. Moreover, we observed non-linear associations between serum calcium and anaemia risk. Our results need to be confirmed in future prospective studies.