Association of serum calcium and metabolically healthy obese in US adults: a cross-sectional study

Abstract

Objectives: The relationship between serum calcium and occurrence of MHO (metabolically healthy obesity) and MUNO (metabolically unhealthy non-obesity) remains unclear, and distinguishing these two phenotypes is difficult within primary healthcare units. This study explores that relationship.

Methods: This survey included 28590 adults from the National Health and Nutrition Examination Survey (NHANES) 2001-2018. Obesity phenotypes were categorized based on BMI and presence or absence of metabolic syndrome components. Weighted multivariate logistic regression analyses were used to assess the association between serum calcium levels and the obesity phenotype. Restricted cubic spline analysis characterized dose-response relationships, and stratified analyses explored these relationships across sociodemographic and lifestyle factors.

Results: The overall prevalence of MHO and MUNO were 2.6% and 46.6%, respectively. After adjusting for covariates, serum calcium exhibited a negative association with MHO [OR (95%): 0.49 (0.36,0.67), p < 0.001], while exhibiting a positive association with MUNO [OR (95%): 1.48 (1.26,1.84), p < 0.001]. Additionally, we found a non-linear association between serum calcium levels and the incidences of MHO and MUNO. Stratified analyses demonstrated a strong negative correlation between serum calcium levels and MHO occurrence across various subgroups. There was no significant interaction between calcium and stratified variables except sex; the association between calcium and the occurrence of MHO was remarkable in female patients. Meanwhile, the predictive ability of serum calcium level for the occurrence of MUNO among all patients was consistent across various subgroups. There was a significant interaction between calcium level and stratified variables based on age, sex, race, and smoking status; the association was remarkable in older (≥ 40 years old), white, none or less smoking, and female patients.

Conclusions: A significant correlation was identified between serum calcium levels and MHO or MUNO. The findings suggest that serum calcium levels may serve as an indicator for more accurate assessment and diagnosis of MUNO and MHO, especially among individuals with abdominal obesity.

Keywords: Metabolically healthy obesity (MHO), metabolically unhealthy non-obese (MUNO), obesity; Nutrition Examination survey (NHANES); serum calcium.

Figure 1.

The selection flowchart of the participants.

Figure 2.

Dose-response associations of serum calcium with incidence of MHO and MUNO in US adults. Association between serum calcium with incidence of MHO (A) and MUNO (B) in US adults. The associations were examined by generalized additive models with restricted cubic splines. ORs adjusted for Model 3 (age, sex, race, education level, family income level, serum ALT, AST, BUN, Scr, eGFR, Vitamin D3, Dietary calcium intake, smoking status, alcohol intake, physical activity, and CVD). Solid lines represent estimates of ORs and dashed lines represent 95% CIs.

Figure 3.

Stratified analyses for the association between serum calcium level as a continuous variable and incidence of MHO. Odds ratio adjusted for variables in the Model 3 (age, sex, race, education level, family income level, serum ALT, AST, BUN, Scr, eGFR, Vitamin D3, Dietary calcium intake, smoking status, alcohol intake, physical activity, and CVD) except the corresponding stratification variable.

Figure 4.

Stratified analyses for the association between serum calcium level as a continuous variable and incidence of MUNO. Odds ratio adjusted for variables in the Model 3 (age, sex, race, education level, family income level, serum ALT, AST, BUN, Scr, eGFR, Vitamin D3, Dietary calcium intake, smoking status, alcohol intake, physical activity, and CVD) except the corresponding stratification variable.