Table 6.

Association between water hardness and incident IBD in the cohort study

		IBD
		Cases	Model 1 HR (95% CI)	P	Model 2 HR (95% CI)	P	Model 3 HR (95% CI)	P
Water hardness (USGS, mg/l)	0–60	1193	ref		ref		ref
	60–120	665	1.00 (0.91–1.1)	0.949	1.01 (0.92–1.11)	0.861	1.02 (0.92–1.12)	0.757
	120–180	184	0.93 (0.79–1.08	0.330	0.95 (0.81–1.11)	0.528	0.95 (0.81–1.11)	0.525
	> 180	1167	0.91 (0.84–0.99)	0.022	0.91 (0.84–0.99)	0.029	0.92 (0.84–1.00)	0.040
	P for trend			0.014		0.019		0.025
Water hardness (WHO, mg/l)	< 200	2059	ref		ref		ref
	≥ 200	1150	0.92 (0.85–0.99)	0.020	0.91 (0.85–0.98)	0.017	0.92 (0.85–0.99)	0.021
CaCO3 concentration (per SD)			0.95 (0.92–0.99)	0.010	0.95 (0.92–0.99)	0.010	0.96 (0.92–0.99)	0.014
Ca concentration (per SD)			1.01 (0.97–1.04)	0.748	1.00 (0.96–1.04)	0.966	1.00 (0.96–1.04)	0.950
Mg concentration (per SD)			0.97 (0.93–1.01)	0.108	0.98 (0.94–1.02)	0.254	0.98 (0.94–1.02)	0.327

Abbreviations: USGS United States Geological Survey, WHO World Health Organization, HR hazards ratio, P p-values

Model 1: adjusted for age and sex

Model 2: adjusted for age, sex, CCI scores, BMI, IPAQ physical activity, alcohol consumption, smoking status, ethnicity, TDI and diet quality scores

Model 3: adjusted for age, sex, CCI scores, BMI, IPAQ physical activity, alcohol consumption, smoking status, ethnicity, TDI, diet quality scores, the first five principal components of ancestry genetics

Bold font for USGS and WHO water hardness groups indicates p < 0.025, while bold font for other variables indicates p < 0.05