Table 1.

Distribution of potential risk factors for breast cancer according to serum T3 level

Factor	T3 quartile
	1	2	3	4	All
	N = 494	N = 704	N = 456	N = 531	N = 2,185
	Column percent (T3 levels in italics)
T3 (mIU/l)	<1.50	1.60 to 1.80	1.90 to 2.00	2.1 to -4.30
Age
<50	62.1	46.6	26.1	21.5	39.7
>50	37.9	53.4	73.9	78.5	60.3
Premenstrual	60.3	44.2	28.7	23.2	39.5
Peri/postmenopausal	39.7	55.8	71.3	76.8	60.5
HRT in peri/postmenopausal	13.3	14.2	15.4	17.6	15.4
missing	-	-	0.3	-	0.1
Nulliparity	18.2	17.0	13.2	19.6	17.1
missing	-	-	0.4	0.8	0.3
OC-use	4.7	6.0	9.0	11.5	7.6
missing	-	-	0.7	0.9	0.4
Menarche <12 years	15.2	13.4	9.6	11.9	12.6
missing	-	0.4	1.3	1.3	0.7
Smoking
never	43.5	47.7	47.6	47.1	46.6
current	35.8	33.2	34.0	33.1	34.0
ex	20.6	19.0	18.0	18.8	19.1
missing	-	-	0.4	0.9	0.3
Alcohol consumption
nothing	14.2	14.1	13.2	19.0	15.1
less than every week	55.3	60.7	62.5	60.1	59.7
every week	30.6	25.1	23.9	19.4	24.7
missing	-	0.1	0.4	1.5	0.5
BMI
<20	14.8	10.1	7.9	7.5	10.1
≥20 <25	62.3	56.1	53.9	46.5	54.7
≥25 <30	17.0	26.1	27.9	30.5	25.5
≥30	5.9	7.7	10.3	15.4	9.7
Height
≤ 160	24.1	28.8	28.9	36.5	29.7
>160 ≤ 165	32.6	33.2	30.9	30.7	32.0
>165 ≤ 170	26.7	24.9	25.0	22.0	24.6
>170	16.6	13.1	15.1	10.7	13.7
Education
<12 years	53.0	53.6	62.5	64.2	57.9
12 years	20.9	27.4	22.1	21.8	23.5
>12 years	21.7	14.9	11.2	10.7	14.5
Missing	4.5	4.1	4.2	3.2	4.0
Married	54.9	54.4	51.3	50.3	52.9
missing	0.8	1.8	7.2	14.5	5.8

Abbreviations: T3, triiodothyronine; HRT, hormone replacementtherapy; OC, oral contraceptives; BMI, body mass index.