Table 3.

Pooled multivariate hazard ratio (HR) of site-specific SCC and melanoma by total niacin intake in the NHS and HPFS

	Quintile of total niacin intake					p for trend
	1	2	3	4	5
Pooled risk on the body sites with higher sun exposure (head, neck, and extremities)
SCC
No. of cases	380	403	394	430	397
Pooled HR1	1 (referent)	0.92 (0.69, 1.23)	0.87 (0.71, 1.05)	0.95 (0.70, 1.29)	0.85 (0.73, 0.98)	0.10
Melanoma
No. of cases	93	106	93	104	115
Pooled HR1	1 (referent)	0.96 (0.72, 1.27)	0.89 (0.48, 1.65)	0.94 (0.71, 1.25)	1.05 (0.77, 1.42)	0.38
Risk of SCC on the body sites with lower sun exposure (trunk and mucosa)
SCC
No. of cases	55	59	63	62	68
Pooled HR1	1 (referent)	0.88 (0.61, 1.28)	0.90 (0.62, 1.31)	0.88 (0.49, 1.58)	0.97 (0.68, 1.40)	0.75
Melanoma
No. of cases	57	71	68	54	76
Pooled HR1	1 (referent)	1.12 (0.74, 1.70)	1.08 (0.67, 1.74)	0.85 (0.58, 1.25)	1.21 (0.63, 2.34)	0.50

¹The multivariate-adjusted HR from each cohort were combined with meta-analytic methods using random effects model. The HR from each cohorts were adjusted for family history of melanoma (yes vs. no), natural hair color (red, blonde, light brown, dark brown and black), number of arm moles (0, 1–2, 3–9 and ≥10), skin reaction to sun exposure as a child/adolescent (none/some redness, burn, painful burn/blisters), number of lifetime blistering sunburns (0, 1–4, 5–9 and ≥10), average time spent in direct sunlight since high school (<2, 2–5, 6–9 and ≥10 hr/wk), cumulative UV flux since baseline (quintiles), body mass index (<25.0, 25.0–29.9, 30.0–34.9 and ≥35.0 kg/m²), physical activity (quintiles), smoking status (never, past, current with 1–14, 15–24 and or ≥25 cigarettes/d), intakes of total energy (quintiles), alcohol (0, 0.1–4.9, 5.0–9.9, 10.0–19.9 and ≥20.0 g/d) and citrus intake (quintiles). Analyses for women were also adjusted for menopausal status and postmenopausal hormone use (premenopausal, postmenopausal never, past or current use.