Table 4.

Multivariate odds ratios (OR) and 95% confidence intervals (CI) for dietary protein intakes 2–4 years prior to reference year and risk of premenstrual syndrome (n=3,638) stratified by age at diagnosis/ reference year; NHS2 PMS Sub-Study, 1991–2005.

Quintile of protein intake, g/day
	Q1	Q2	Q3	Q4	Q5	P for interaction
Total protein
<40 years old	1.00 (Ref)	0.71 (0.48 – 1.07)	0.65 (0.42 – 1.02)	0.68 (0.43 – 1.06)	0.80 (0.48 – 1.31)	<0.0001
≥ 40 year old	1.00 (Ref)	0.66 (0.47 – 0.92)	1.05 (0.75 – 1.47)	1.01 (0.70 – 1.45)	1.02 (0.68 – 1.51)
Animal protein
<40 years old	1.00 (Ref)	0.74 (0.49 – 1.12)	0.73 (0.48 – 1.12)	0.63 (0.40 – 1.00)	0.58 (0.35 – 0.96)	<0.0001
≥ 40 year old	1.00 (Ref)	0.87 (0.63 – 1.20)	1.06 (0.76 – 1.48)	1.11 (0.77 – 1.58)	0.95 (0.64 – 1.40)
Vegetable protein
<40 years old	1.00 (Ref)	0.84 (0.56 – 1.26)	1.38 (0.92 – 2.06)	1.55 (1.01 – 2.38)	1.70 (1.10 – 2.62)	<0.0001
≥ 40 year old	1.00 (Ref)	1.04 (0.75 – 1.45)	0.81 (0.57 – 1.14)	0.72 (0.50 – 1.03)	1.06 (0.74 – 1.52)
Dairy protein
<40 years old	1.00 (Ref)	1.16 (0.74 – 1.82)	1.10 (0.68 – 1.79)	1.00 (0.61 – 1.65)	0.74 (0.42 – 1.30)	0.0001
≥ 40 year old	1.00 (Ref)	1.12 (0.80 – 1.57)	1.02 (0.72 – 1.45)	0.91 (0.63 – 1.33)	0.95 (0.62 – 1.46)

Ref, reference category

^*Models are adjusted for age, reference year, age at menarche, body mass index, physical activity, oral contraceptive use, parity, smoking status, ever use of antidepressants, childhood trauma, vitamin D from dietary sources and total intake of vitamins B6, B1, iron, and zinc at 2–4 years before reference year.