Causal associations between tea and milk consumption and the risk of kidney stones: A two-sample Mendelian randomization study

The causal associations between tea and milk consumption and the risk of kidney stones remain uncertain, as inconsistent results have been reported in traditional observational studies. We performed a two-sample Mendelian randomization analysis to assess the causal effects of tea and milk consumption on the risk of kidney stones. We selected independent single nucleotide polymorphisms at the genome-wide significance threshold of P < 5 × 10 -8 as instrumental variables (IVs). Summary-level data for tea (up to 501,534 individuals) and milk (up to 73,715 individuals) were obtained from corresponding genome-wide association studies. Summary-level data for kidney stones were identified from the UK Biobank (6430 cases and 415,001 non-cases) and the FinnGen study (12,999 cases and 486,185 non-cases). The causal effects were estimated using the multiplicative random effect-inverse variance weighted method and other five methods, and were reported using odds ratios (ORs) and 95% confidence intervals (CIs). Heterogeneity and pleiotropy of IVs were also assessed. Genetically predicted per additional daily cup of tea consumption was associated with a lower risk of kidney stones in the FinnGen consortium (OR = 0.70, 95% CI: 0.58, 0.83; P < 0.0001). Genetic predisposition to milk consumption was associated with a lower risk of kidney stones in the FinnGen consortium (OR = 0.93, 95% CI: 0.88, 0.97; P = 0.0013), and the association was directionally similar in the UK Biobank study. The OR for the association between kidney stones and an increase of one cup of milk per week was 0.93 (95% CI: 0.89, 0.97; P = 0.0010) in the meta-analysis of these two data sources. This study provides evidence that genetic predispositions to higher tea and milk consumption are associated with the decreased risk of kidney stones. Increasing tea and milk consumption could be considered as a prevention strategy for kidney stones.