Table 3.

Serum 25-Hydroxy Vitamin D and Risk of Upper Respiratory Tract Infection in Health Diary Participants (n = 758)

Episodes	All Rate Ratioa (95% CI)	Quartiles of Serum Vitamin D Closest to 1 November 2009b
		1: Ref	2: RR (95% CI)	3: RR (95% CI)	4: RR (95% CI)	P Value for Heterogeneity
Winter
URTI	0.93 (.86–1.01)	1.0	0.94 (.74–1.19)	0.97 (.76–1.23)	0.86 (.68–1.10)	.66
Colds	0.94 (.87–1.02)	1.0	1.01 (.79–1.30)	1.01 (.79–1.29)	0.92 (.72–1.18)	.83
ILI	0.87 (.68–1.10)	1.0	0.41 (.23–0.73)	0.70 (.39–1.25)	0.50 (.27–.94)	.01
All seasons
URTI	0.91 (.83–.99)	1.0	0.87 (.66–1.13)	0.86 (.66–1.12)	0.79 (.61–1.02)	.34
Colds	0.91 (.83–1.00)	1.0	0.91 (.69–1.20)	0.90 (.68–1.18)	0.82 (.63–1.07)	.54
ILI	0.84 (.68–1.04)	1.0	0.47 (.28–.78)	0.59 (.36–.98)	0.51 (.30–.85)	.01
Days of illness
Winter
Any	0.96 (.85–1.10)	1.0	0.96 (.65–1.40)	1.07 (.73–1.57)	0.91 (.61–1.34)	.79
Moderate	0.97 (.85–1.11)	1.0	0.97 (.66–1.43)	1.10 (.74–1.63)	0.93 (.62–1.40)	.78
Severe	0.84 (.63–1.11)	1.0	0.58 (.30–1.12)	0.60 (.32–1.12)	0.49 (.24–.99)	.13
All seasons
Any	0.95 (.84–1.07)	1.0	0.90 (.60–1.34)	0.96 (.66–1.46)	0.86 (.58–1.27)	.85
Moderate	0.95 (.84–1.08)	1.0	0.91 (.61–1.37)	0.99 (.67–1.45)	0.87 (.59–1.30)	.86
Severe	0.82 (.63–1.07)	1.0	0.52 (.28–.95)	0.52 (.29–.92)	0.49 (.26–.91)	.04

Abbreviations: CI, confidence interval; ILI, influenza-like illness; RR, rate ratio; URTI, upper respiratory tract infection (cold or ILI).

^a Rate ratio per 10 ng/mL change in serum 25-hydroxy vitamin D, adjusted for season of closest blood draw (December–February, March–May, June–August, September–November), age, sex, race (white, black, Asian, other), Hispanic ethnicity, body mass index, northern latitude, smoking status (never, former, current), activity level (low, moderate, high), artificial tanning (no/yes), total annual vacation days in a warm climate.

^b Quartiles based on distribution of 758 participants: 25th, 50th, and 75th percentiles (21.75, 28.42, 35.4 ng/mL).