Table 2. RRs of colorectal cancer by dose and duration of aspirin use in a cohort of 74 250 Swedish women and men, 1998–2005.

	Colorectal cancer				Colon cancer		Rectal cancer
Aspirin	No. of casesa	Person-years of follow-up	Age- and sex-adjusted RR (95% CI)	Multivariate RR (95% CI)b	No. of casesa	Multivariate RR (95% CI)b	No. of casesa	Multivariate RR (95% CI)b
Nonusec	417	304 321	1.00 (reference)	1.00 (reference)	271	1.00 (reference)	149	1.00 (reference)
Use	288	230 610	0.89 (0.76–1.03)	0.87 (0.75–1.01)	185	0.84 (0.69–1.02)	104	0.92 (0.72–1.19)
No. of tablets/week
1	45	42 545	0.85 (0.62–1.16)	0.83 (0.61–1.14)	26	0.73 (0.48–1.09)	20	1.07 (0.67–1.72)
2–6	65	52 524	0.91 (0.70–1.18)	0.88 (0.68–1.16)	38	0.77 (0.55–1.09)	27	1.09 (0.72–1.65)
>6	70	44 954	0.80 (0.62–1.04)	0.77 (0.59–0.99)	41	0.75 (0.55–1.03)	24	0.79 (0.51–1.22)
P-value for trend			0.09	0.04		0.05		0.37
Years of aspirin use
1–10	52	81 165	0.98 (0.80–1.19)	0.96 (0.78–1.17)	78	0.88 (0.68–1.13)	50	1.09 (0.79–1.52)
11–20	27	24 901	0.89 (0.60–1.31)	0.87 (0.59–1.29)	19	0.93 (0.58–1.49)	8	0.73 (0.36–1.51)
>20	31	35 481	0.66 (0.46–0.96)	0.65 (0.45–0.94)	23	0.76 (0.49–1.16)	9	0.52 (0.26–1.02)
P-value for trend			0.03	0.02		0.20		0.04

CI=confidence interval; RR=rate ratio;

^aThe number of cases may not sum up to the total number of cases owing to missing information on number of tablets and years of aspirin use. Four cases that were diagnosed with both colon and rectal cancer were included in analysis of both cancer sites.

^bMultivariate RRs were adjusted for baseline age, sex, education, family history of colorectal cancer, body mass index, leisure-time physical activity, history of diabetes, and smoking.

^cReference group for all comparisons.