Table 2.

Rotating night shift work duration and colorectal cancer risk in the Nurses’ Health Study, 1988–2012 (N = 77,439)

	No. of cases	Person‐yrs	RR (95% CI)1	p‐trend1 , 3	RR (95% CI)2	p‐trend2 , 3
NHS baseline rotating night shift work history in years
Never	584	634,953	1.0 (ref)		1.0 (ref)
1–2	346	376,925	1.02 (0.90, 1.17)		1.04 (0.91, 1.19)
3–4	269	257,258	1.05 (0.91, 1.22)		1.05 (0.91, 1.22)
5–9	112	104,179	1.08 (0.88, 1.32)		1.06 (0.87, 1.30)
10–14	73	69,547	1.04 (0.82, 1.33)		1.01 (0.79, 1.29)
15–19	45	42,259	1.05 (0.78, 1.43)		1.02 (0.75, 1.39)
20–29	59	41,964	1.34 (1.02, 1.76)		1.26 (0.96, 1.65)
30+	39	24,740	1.21 (0.87, 1.68)	0.04	1.17 (0.84, 1.63)	0.14
	1,527	1,551,827
NHS baseline rotating night shift work history in years 4
Never	584	634,953	1.0 (ref)		1.0 (ref)
1–14	800	807,909	1.04 (0.94, 1.16)		1.04 (0.94, 1.16)
15+	143	108,964	1.20 (1.00, 1.45)		1.15 (0.95, 1.39)
	1,527	1,551,827

¹ Adjusted for age (months) and follow‐up cycle.

² Adjusted for age (months), height (continuous in inches), BMI (<18.5, 18.5–24.9, 25.0–29.9, ≥30 kg/m²), educational level (RN license, bachelor's degree, masters or doctoral degree), menopausal status (premenopausal, postmenopausal), menopausal hormone therapy (never, past, current), first‐degree family history of colorectal cancer (yes, no), alcohol consumption (0, 0.1–4.9, 5–14.9, ≥15 g/day), physical activity (≤8, 8.1–16, 16.1–24, >24 MET‐hr/week), smoking status (never smoker, current smoker, past smoker), colonoscopy/sigmoidoscopy in the previous 2 years (yes, no), current regular aspirin or NSAIDS use (>2 tablets/week), daily energy intake (kcal/day), red or processed meat (servings/day) and folate consumption (ug/day) in quintiles.

³ p‐trend was calculated using the midpoint of each category of rotating shift work duration in years (1–2, 3–4, 5–9, 10–14, 15–19, 20–29, 30+).

⁴ Categories of shift work duration (Never, 1–14 years, 15+ years) were used to compare with our previously published results.