Correlations between heavy metals and chronic diarrhea and constipation in US adults

Background: Heavy metals such as lead, mercury, and cadmium are closely related to human health. However, their correlations with chronic constipation and diarrhea have not been systematically studied. Aims To evaluate the associations between the blood levels of lead, cadmium, and mercury with chronic constipation and diarrhea. Methods First, we collected and analyzed the National Health and Nutrition Examination Survey (NHANES) (2009–2010) dataset from the USA. Then, we evaluated the associations between heavy metals and chronic diarrhea and constipation using the survey generalized linear model (SVYGLM), and the weighted quantile sum (WQS) regression. Finally, we used restricted cubic splines (RCS) models to determine the dose-response relationship between heavy metals and the prevalence of chronic diarrhea and constipation. Results The blood levels of cadmium were positively correlated with chronic diarrhea [ p  = 0.002, odds ratio (OR) = 1.33, 95% confidence interval (CI): 1.14–1.54] and the blood levels of lead were negatively correlated with chronic constipation ( p  = 0.01, OR = 0.84, 95% CI: 0.75–0.95) by the SVYGLM. Based on the WQS regression, the blood levels of cadmium were positively correlated with chronic diarrhea ( p  = 0.008, OR = 1.21, 95% CI: 1.05–1.39), the blood levels of lead were negatively correlated with chronic constipation ( p  = 0.016, OR = 0.91, 95% CI: 0.85–0.98), and the levels of mercury were negatively correlated with chronic constipation ( p  = 0.008, OR = 0.93, 95% CI: 0.89–0.98). Morever, a linear dose-response association was detected between the blood concentration of cadmium and the prevalence of chronic diarrhea (nonlinearity p  = 0.51). Additionally, a non-linear dose-response association was detected between blood concentration of lead and the prevalence of chronic constipation (nonlinearity p  = 0.002). Conclusion The blood levels of cadmium were positively associated with chronic diarrhea, and the blood levels of lead and mercury were inversely associated with chronic constipation.