Associations of adiposity, kidney stone disease, and serum calcium concentrations; observational and genetic epidemiological studies

Background Kidney stone disease (KSD) is linked to obesity, metabolic syndrome and biochemical alterations including higher serum calcium concentration. The mechanisms by which these phenotypes associate with KSD are uncertain. We aimed to establish the effects of adiposity on KSD using conventional and genetic epidemiological techniques. Methods We assessed observational associations between measures of adiposity and incident KSD in 479,405 people from the UK Biobank. To facilitate Mendelian randomization (MR) analyses, we undertook genome-wide association studies (GWAS) of KSD in the UK Biobank in combined and sex-specific subsets. Univariable, multivariable and mediation MR analyses were used to calculate odds ratio (OR) or beta coefficient (ß) for risk of KSD per genetically instrumented higher marker of adiposity, metabolic syndrome parameter, biochemical phenotype, and inflammation and identify violations of MR assumptions. Findings Observational analyses demonstrated that measures of central adiposity (waist-to-hip ratio (WHR) and waist circumference (WC)) are more strongly associated with incident KSD than measures of general adiposity (body mass index (BMI)). Three novel KSD-GWAS loci were identified ( SLC2A12, TRPV5 , and SLC28A1 ); no sex-specific loci were detected. MR analyses established that higher central adiposity is causally linked to both KSD and higher adjusted serum calcium concentrations independent of BMI (one standard deviation higher WHR: OR for KSD=1·43, p=4·1×10 −6 ; ß for serum calcium concentration=0·11mmol/L, p=2·7×10 −7 ). Mediation analyses indicated that 12% of the effect of WHR on KSD is due its role in elevating serum calcium concentration. Our MR studies indicated that other components of the metabolic syndrome, serum uric acid levels, and biomarkers of inflammation are unlikely to be implicated in the causation of KSD. Interpretation Our study indicates that visceral adipose depots elevate serum calcium concentration and cause an increased risk of KSD. Therapies targeting central adipose deposition may affect calcium homeostasis and have utility for the prevention of KSD.