Table 4.

Multivariate OR and 95 % CI for dietary protein intakes (g/d) 2–4 years prior to the reference year and risk of premenstrual syndrome (PMS; n 3638), stratified by age at the reference year; Nurses’ Health Study II PMS Sub-Study, 1991–2005

	Quintile 1		Quintile 2		Quintile 3		Quintile 4		Quintile 5
	OR	95 % CI	OR	95 % CI	OR	95 % CI	OR	95 % CI	OR	95 % CI	P 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 years 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 years 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 years 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 years 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, BMI, physical activity, oral contraceptive use, parity, smoking status, ever use of antidepressants, childhood trauma, vitamin D from dietary sources and total intake of vitamin B₆, thiamin, Fe and Zn at 2–4 years prior to the reference year.