. Author manuscript; available in PMC: 2016 Jul 1.

Published in final edited form as: Int J Cancer. 2014 Dec 8;137(1):173–182. doi: 10.1002/ijc.29365

Table 3.

Ovarian cancer risk in relation to nitrate-nitrogen (NO₃-N) levels in drinking water stratified by high or low total vitamin C and red meat intake

	Vitamin C ≤ 190 mg/d				Vitamin C >190 mg/d				p_interaction
	N	Cases	HR (95% CI)^a	p_trend	N	Cases	HR (95% CI)^a	p_trend	p_interaction
	NO₃-N (mg/L)
0.01 – 0.472	1,625	7	1.0	0.005	1,638	16	1.0	0.12	0.33
0.473 – 1.08	1,629	14	1.85 (0.74 – 4.65)		1,640	18	1.16 (0.59 – 2.29)
1.09 – 2.97	1,762	26	3.17 (1.37 – 7.32)		1,742	15	0.83 (0.40 – 1.70)
2.98 – 25.34	1,467	24	3.39 (1.45 – 7.95)		1,548	25	1.60 (0.85 – 3.02)
Private well water^b	2,125	29	3.30 (1.44 – 7.56)	-	2,040	16	0.77 (0.38 – 1.54)	-	0.01

	Red meats ≤ 5 servings/wk				Red meats >5 servings/wk
	N	Cases	HR (95% CI)^a	p_trend	N	Cases	HR (95% CI)^a	p_trend

NO₃-N (mg/L)
0.01 – 0.472	1,812	13	1.0	0.18	1,451	10	1.0	0.002	0.14
0.473 – 1.08	1,853	21	1.61 (0.81 – 3.22)		1,416	11	1.04 (0.43 – 2.50)
1.09 – 2.97	2,032	26	1.69 (0.86 – 3.30)		1,472	15	1.36 (0.60 – 3.06)
2.98 – 25.34	1,788	25	1.82 (0.93 – 3.57)		1,227	24	2.59 (1.23 – 5.48)
Private well water^b	1,629	15	1.34 (0.64 – 2.82)	-	2,536	30	1.68 (0.82 – 3.44)	-	0.63

Adjusted for age, BMI, family history of ovarian cancer, number of live births (0, 1–2, 3–4, ≥ 5), age at menarche (≤ or >12), age at menopause (< 45, 45–49, 50–54, ≥ 55), age at first live birth (< 20, 20–24, 25–29, ≥ 30), oral contraceptive use (never, ever), estrogen use (never, ever), and a history of unilateral oophorectomy.

HR and 95% CI were computed with the lowest quartile of nitrate among public water drinkers as a reference group.