Table 3.

Relative risks (RR) and 95% confidence intervals of breast cancer across quartiles of creatinine-standardized urinary melatonin level (n=1,354)

	Quartiles of urinary melatonin levels (in ng/mg creatinine)
	Quartile 1	Quartile 2	Quartile 3	Quartile 4	p-trend
Invasive + in situ cases combined
No. of cases / no. of controls	162 / 200	148 / 199	136 / 201	109 / 199
Simple RR a	1.00 (ref)	0.95 (0.76–1.19)	0.90 (0.72–1.13)	0.79 (0.62–1.01)	0.08
Multivariable RR b	1.00 (ref)	0.96 (0.77–1.20)	0.92 (0.73–1.16)	0.78 (0.61–0.99) c	0.08
Invasive cases only
No. of cases / no. of controls	121 / 156	114 / 154	111 / 150	87 / 161
Simple RR a	1.00 (ref)	0.97 (0.75–1.26)	0.97 (0.75–1.26)	0.80 (0.61–1.06)	0.15
Multivariable RR b	1.00 (ref)	0.99 (0.76–1.28)	1.01 (0.78–1.31)	0.80 (0.61–1.07)	0.19
In situ cases only
No. of cases / no. of controls	41 / 44	34 / 45	25 / 51	22 / 38
Simple RR a	1.00 (ref)	0.89 (0.57–1.41)	0.68 (0.42–1.12)	0.76 (0.45–1.28)	0.29
Multivariable RR b	1.00 (ref)	0.84 (0.52–1.35)	0.63 (0.38–1.06)	0.62 (0.36–1.07)	0.09

^aSimple conditional logistic regression model.

^bMultivariable conditional logistic regression model adjusted for the following: age at menarche (<12, 12, 13, ≥14 years), age at menopause (≤45, 46–50, 51–53, ≥54 years), parity (nulliparous, 1–2, 3–4, or ≥5 children), family history of breast cancer (mother or sister: yes, no), BMI (continuous in kg/m²), alcohol intake (0, 1–14.9, ≥15 g/day), smoking status (current: yes, no), history of benign breast disease (yes, no), antidepressant use (current: yes, no), PMH (current: yes, no), type and duration of PMH (estrogen only: 0, <5, ≥5 years; estrogen + progesterone: 0, <5, ≥5 years), and first morning urine (yes, no).

^cThis estimate is statistically significant because the 95% confidence interval does not include the null value of 1.00.