Table 2.

Association between nitrate-nitrogen (NO₃-N) and total trihalomethanes (TTHM) in public water supplies and pancreatic cancer among Iowa Women’s Health Study participants > 10 years at their drinking water source.^a

			Model 1b	Model 2c
Drinking water nitrate	Cases	N	HR (95% CI)	HR (95% CI)
Private welld	34	4,955	0.92 (0.56, 1.52)	-
Average NO3-N (mg/L)
< 0.47	31	4,007	1.00 (Ref.)	1.00 (Ref.)
0.47 – 1.08	41	3,875	1.40 (0.88, 2.24)	1.44 (0.90, 2.30)
1.09 – 2.97	48	4,163	1.51 (0.96, 2.37)	1.56 (0.99, 2.46)
2.98-5.69	25	2,868	1.14 (0.67, 1.93)	1.16 (0.69, 1.98)
>5.69e	7	797	1.18 (0.52, 2.67)	1.16 (0.51, 2.64)
ptrend			0.97	0.97
Continuous f	152	15,710	1.07 (0.92, 1.25)	1.08 (0.93, 1.25)
Years >½ MCL (>5mg/L NO3-N)
0	99	11,026	1.00 (Ref.)	1.00 (Ref.)
1-4	34	2,318	1.66 (1.12, 2.44)	1.65 (1.12, 1.48)
≥4	19	2,366	0.90 (0.55, 1.47)	0.90 (0.55, 1.48)
ptrend			0.59	0.62
Continuousg	152	15,710	0.99 (0.93, 1.06)	0.99 (0.93, 1.06)
Average TTHM (μg/L)
<0.90	37	3,781	1.00 (Ref.)	1.00 (Ref.)
0.90-4.58	52	4,339	1.24 (0.81-1.90)	1.22 (0.80-1.86)
4.59-14.31	39	4,182	0.95 (0.61-1.49)	0.88 (0.55-1.40)
>14.30	24	3,408	0.73 (0.44-1.22)	0.70 (0.42-1.18)
ptrend			0.07	0.06
Continuous f	152	15,710	0.99 (0.94-1.04)	0.98 (0.94-1.04)
Years >½ MCL (>40 μg/L TTHM)
0	116	11,909	1.00 (Ref.)	1.00 (Ref.)
1-36	17	1,696	1.02 (0.62-1.70)	1.02 (0.62-1.69)
≥ 36	19	2,105	0.94 (0.58-1.52)	0.94 (0.58-1.52)
ptrend			0.79	0.79
Continuous h	152	15,710aa	1.00 (0.98-1.01)	1.00 (0.98-1.01)

^aAfter excluding 200 women with missing covariate data.

^bAdjusted for age and smoking status.

^cAdjusted for age, smoking status, and mutually adjusted for natural log-transformed TTHM or NO₃-N.

^dCompared to women in the 1^st quartile (< 0.47 mg/L) of nitrate exposure in public water supplies.

^e95^th percentile.

^fHR per 1 natural log increase in concentration.

^gHR per year increase in exposure >5 mg/L NO₃-N.

^hHR per year increase in exposure >40 μg/L TTHM.