Table 4.

Joint effects of average drinking water nitrate concentration and red meat intake on bladder cancer among New England Bladder Cancer Study participants with a nitrate estimate for >=70% of exposure-years from 1970 to diagnosis/reference date (777 cases and 940 controls)^a

Total red meat intake
	< 31 g / day		≥ 31 g / day
Average nitrate concentration (mg/L NO3-N)b	Cases/Controls	OR (95% CI)c	Cases/Controls	OR (95% CI)c	P-intc,d
≤0.21 mg/L	103/110	1.0 Ref	97/124	0.82 (0.55-1.2)
>0.21-0.37 mg/L	77/113	0.75 (0.50-1.2)	86/117	0.80 (0.52-1.2)
>0.37-0.68 mg/L	78/124	0.78 (0.67-1.6)	108/105	1.1 (0.71-1.7)
>0.68-2.07 mg/L	84/91	1.0 (0.33-1.4)	89/107	0.88 (0.57-1.4)
>2.07 mg/L	18/29	0.69 (0.55-1.2)	37/20	2.6 (1.3-5.1)
					0.05
Processed red meat intake
	< 6.5 g / day		≥ 6.5 g / day
Average nitrate concentration (mg/L NO3-N)b	Cases/Controls	OR (95% CI)c	Cases/Control	OR (95% CI)c	P-intc,d
≤0.21 mg/L	79/115	1.0 Ref.	121/119	1.5 (1.0-2.3)
>0.21-0.37 mg/L	75/116	1.1 (0.67-1.7)	88/114	1.1 (0.72-1.8)
>0.37-0.68 mg/L	88/127	1.2 (0.76-1.8)	98/102	1.4 (0.92-2.2)
>0.68-2.07 mg/L	73/85	1.5 (0.92-2.4)	100/113	1.3 (0.81-2.0)
>2.07 mg/L	21/28	1.1 (0.55-2.2)	34/21	3.5 (1.8-6.9)
					0.07

^aAverage nitrate concentrations in residential and workplace public water supplies and measured and modeled private wells; participants with missing water intake, extreme energy intake (1^st or 99^th percentiles of total kcal) or missing dietary data were excluded

^bExposure categories represent quartiles, with the top category reflecting an additional cut at 95th percentile

^cAdjusted for age, gender, smoking status, high-risk occupation, race, ethnicity, state, average total trihalomethane concentration and total water intake (L/d)

^dP-value for interaction computed from likelihood ratio test comparing nested models with and without interaction terms

CI indicates confidence interval, OR odds ratio.