Table 5.

Joint associations of remote period^a and recent period^b duration of aspirin use with CRC risk in the NHS and HPFS

Pooled NHS and HPFS	Joint associations according to duration of aspirin use and timing				P interaction d
	Low to lowc	Low to highc	High to lowc	High to highc
No. of CRC cases (2147 in total)	1225	437	201	284
Age-adjusted model, HR (95% CI)e	1 (Reference)	0.80 (0.72 to 0.90)	0.78 (0.67 to 0.91)	0.65 (0.57 to 0.74)	.72
MV-adjusted model, HR (95% CI)f	1 (Reference)	0.82 (0.73 to 0.92)	0.79 (0.68 to 0.92)	0.67 (0.58 to 0.77)	.75

^aRemote period duration of aspirin use: duration of regular aspirin use during every specific remote period (>10 years before every follow-up period, ie, begin from 1980 [NHS] and 1986 [HPFS], and then was extended by every 2-year subsequent interval at a time, until 2002). AHEI = Alternate Healthy Eating Index score; BMI = body mass index; CI = confidence interval; CRC = colorectal cancer; HPFS = Health Professionals Follow-up Study; HR = hazard ratio; MV = multivariable; NHS = Nurses’ Health Study; NSAIDs = nonsteroidal antiinflammatory drugs.

^bRecent period duration of aspirin use: duration of regular aspirin use during every specific subsequent 10-year period after the remote periods.

^cAdjusted for age and follow-up cycle in the follow-up period.

^dAdjusted for age, follow-up cycle, sex, race, pack-years of smoking, physical activity, BMI, alcohol consumption, AHEI, regular use of nonaspirin NSAIDs, family history of CRC, history of diabetes mellitus, screening colonoscopy or sigmoidoscopy in the past 2 years, multivitamin use, total calorie intake, red or processed meat intake, fiber intake, folate intake, calcium intake, and vitamin D intake in the follow-up period.

^eRemote period duration of aspirin use and recent period duration of aspirin use were dichotomized into low category (≤5 years) vs high category (>5 years), resulting in 4 categories (low to low, low to high, high to low, and high to high, ie, low remote to low recent, low remote to high recent, high remote to low recent, and high remote to high recent duration of aspirin use).

^f P _interaction was calculated using the multiplication of mid-point of each low or high category of duration of aspirin use in years.