Table 5.

Relative risks (RR) and 95% confidence intervals (CI) according to joint intake of nitrite or nitrate and vitamin C and risk of thyroid cancer

Joint intake Nitrite and/or nitrate/vitamin C	Low/high	Low/low	High/high	High/low	p interaction
Thyroid Cancer
Dietary vitamin C, median intake†	117.4	58.8	117.4	58.8
Nitrate, total, median intake†	134.2	134.2	244.1	244.1
Number of cases	17	47	37	13
Multivariate RR (95% CI)‡	1.00	0.98 (0.54–1.77)	0.93 (0.52–1.68)	1.03 (0..46–2.29)	0.77
Nitrite, total, median intake†	0.71	0.71	1.05	1.05
Number of cases	16	44	38	16
Multivariate RR (95% CI)‡	1.00	1.12 (0.62–2.04)	1.13 (0.63–2.03)	1.16 (0.56–2.41)	0.83

^*Low-high distinctions based on median intake values.

^†mg/1,000 kcal per day.

Adjusted for age (continuous), total energy intake (continuous), education, and history of thyroid disease.