Table 4 Hazard ratios (HR) and 95% confidence intervals (95% CI) of breast cancer death stratified by selected characteristics by quartile of vitamin C intake among 3405 invasive breast cancer cases in the Swedish Mammography Cohort

	Quartile of vitamin C intake (mg d⁻¹)
	<42.9	42.9–65.5	65.6–92.4	⩾92.5	P _trend ^a
Age
<65
Breast cancer deaths	56	53	54	58
Covariate-adjusted model+clinical characteristics^b	1.00	0.91 (0.62–1.34)	0.81 (0.55–1.19)	1.09 (0.75–1.59)	0.69
⩾65
Breast cancer deaths	72	50	43	30
Covariate-adjusted model+clinical characteristics^b	1.00	0.88 (0.61–1.28)	0.76 (0.52–1.12)	0.48 (0.31–0.74)	0.0007
P_interaction^c=0.03
BMI
<30
Breast cancer deaths	102	84	90	74
Covariate-adjusted model+clinical characteristics^b	1.00	0.86 (0.64–1.15)	0.84 (0.63–1.12)	0.80 (0.59–1.09)	0.17
⩾30
Breast cancer deaths	21	18	4	8
Covariate-adjusted model+clinical characteristics^b	1.00	1.33 (0.64–2.77)	0.36 (0.12–1.10)	0.54 (0.22–1.35)	0.04
P_interaction^c=0.30
Smoking
Never smoker
Breast cancer deaths	25	22	17	19
Covariate-adjusted model+clinical characteristics^b	1.00	0.80 (0.44–1.45)	0.55 (0.29–1.04)	0.53 (0.28–0.99)	0.03
Ever smoker
Breast cancer deaths	18	12	12	20
Covariate-adjusted model+clinical characteristics^b	1.00	0.93 (0.42–2.02)	0.70 (0.33–1.49)	1.82 (0.90–3.67)	0.14
P_interaction^c=0.10

^aDetermined using category medians.
^bCox proportional hazard model adjusted for age (continuous), energy intake (continuous), education level (primary, high school, university), marital status (single, married, divorced, widowed, living with partner), menopausal status at diagnosis, (premenopausal, postmenopausal, unknown), body mass index (<20, 20–24.9, 25–29.9, ⩾30 kg m⁻²), alcohol intake (non-drinker, <3.4, 3.4–9.9, ⩾10 g d⁻¹), calendar year of diagnosis (continuous), disease stage (I, II, III/IV), grade (I, II, III), radiation treatment (yes/no) and chemotherapy and/or hormonal treatment (no chemotherapy or hormonal treatment, hormonal therapy and no chemotherapy, chemotherapy and no hormonal therapy, and hormonal therapy and chemotherapy). BMI is not adjusted for in models stratified by BMI and alcohol intake is not adjusted for in models stratified by alcohol.
^cP-value from likelihood ratio test comparing a model with the cross-product term between vitamin C and potential effect modifier to the model with main effects only.

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