Table 2.

Relative Risks (RR) and 95% confidence intervals (CI) for ovulatory infertility by categories of multivitamin supplement use.

	Cases / Non-cases *	Age-Adjusted † RR (95% CI)	Multivariate-Adjusted ‡ RR (95% CI)
Multivitamin Use
Non Users	224 / 10,926	1.00 (referent)	1.00 (referent)
Users	214 / 15,607	0.67 (0.55, 0.80)	0.65 (0.53, 0.80)
Frequency of use
Non Users	224 / 10,926	1.00 (referent)	1.00 (referent)
≤ 2 tablets/wk	32 / 1,808	0.84 (0.58, 1.23)	0.88 (0.60, 1.28)
3 – 5 tablets/ wk	52 / 3,796	0.66 (0.49, 0.90)	0.69 (0.51, 0.95)
≥ 6 tablets/ wk	127 / 9,783	0.63 (0.51, 0.79)	0.59 (0.46, 0.75)
P trend §		<0.001	<0.001

^*223 multivitamin users (3 cases and 220 non-cases) did not provide information about the frequency of multivitamin use.

^†Adjusted for age (continuous) and calendar time (4 two-year intervals).

^‡Age adjusted model further adjusted for total energy intake (continuous), body mass index (<20, 20–24.9, 25–29.9, ≥30 and missing), parity (0, 1, ≥2 and missing), smoking history (never, past 1–4 cig/day, past 5–14 cig/day, past 15–24 cig/day, past ≥ 25 cig/day or unknown amount, current 1–4 cig/day, current 5–14 cig/day, current 15–24 cig/day and current ≥ 25 cig/day or unknown amount), physical activity (<3 MET-h/wk, 3–8.9 METh/wk, 9–17.9 MET-h/wk, 18–26.9 MET-h/wk, 27–41.9 MET-h/wk, ≥ 42 MET-h/wk and missing), contraceptive use (current user, never user, past user 0–23 months ago, past user 24–47 months ago, past user 48–71 months ago, past user 72–95 months ago, past user 96–119 months ago, past user ≥ 120 months ago and missing), and intakes of alcohol (no intake, < 2 g/day, 2–4.9 g/day, ≥ 5 g/day), coffee (<1 serving/month, 1 serving/month, 2–6 servings/week, 1 serving/day, 2–3 servings/day, ≥ 4 servings/day), major types of fatty acids and protein.

^§Calculated with the median frequency of use in each category as a continuous variable.