Table 4.

Relative risks (RR) and 95% confidence intervals (CI) according to quartiles of nitrate or nitrite intake and thyroid cancer in the Shanghai Women’s Health Study

	median (mg/1,000kcal)	Thyroid Cancer (n= 164)
Nitrate		Cases	RR *	95% CI	RR &	95% CI
Quartile 1	109	34	1.00	(ref)	1.00	(ref)
Quartile 2	164	56	1.81	1.18–2.76	1.69	1.07–2.68
Quartile 3	218	41	1.44	0.92–2.28	1.23	0.71–2.15
Quartile 4	251	33	1.32	0.82–2.14	0.93	0.42–2.07
p-value for trend			0.37		0.40
Nitrite
Quartile 1	0.6	32	1.00	(ref)	1.00	(ref)
Quartile 2	0.8	51	1.60	1.03–2.51	1.64	1.04–2.58
Quartile 3	0.9	31	1.05	0.64–1.73	1.09	0.65–1.85
Quartile 4	1.1	50	1.91	1.22–3.00	2.05	1.20–3.51
p-value for trend			0.19		0.36
Plant sources of nitrite
Quartile 1	0.5	37	1.00	(ref)	1.00	(ref)
Quartile 2	0.7	47	1.32	0.85–2.03	1.30	0.83–2.02
Quartile 3	0.8	39	1.19	0.75–1.86	1.15	0.71–1.87
Quartile 4	1.0	41	1.37	0.88–2.15	1.30	0.76–2.4
p-value for trend			0.37		0.70
Animal sources of nitrite
Quartile 1	0.1	30	1.00	(ref)	1.00	(ref)
Quartile 2	0.1	35	1.03	0.63–1.69	1.03	0.63–1.68
Quartile 3	0.1	48	1.41	0.88–2.26	1.35	0.84–2.16
Quartile 4	0.2	51	1.59	1.01–2.56	1.59	1.00–2.52
p-value for trend			0.02		0.02
Processed meat sources of nitrite
Quartile 1	0.0	59	1.00	(ref)	1.00	(ref)
Quartile 2	0.0	19	0.81	0.48–1.36	0.77	0.46–1.31
Quartile 3	0.0	49	1.17	0.80–1.72	1.20	0.81–1.75
Quartile 4	0.1	37	1.92	1.26–2.93	1.96	1.28–2.99
p-value for trend			<0.01		<0.01

^*Adjusted for age (continuous), total energy intake (continuous), education, and history of thyroid disease& Adjusted for age (continuous), total energy intake (continuous), education, history of thyroid disease, vitamin C, carotene, and folate intake.