Dietary Protein Intake and Early Menopause in the Nurses' Health Study II.

Early menopause, which is the cessation of ovarian function before age 45 years, affects 5%-10% of Western women and is associated with an increased risk of adverse health outcomes. Literature suggests that high levels of vegetable protein intake may prolong female reproductive function. We evaluated the association of long-term intake of vegetable protein, animal protein, and specific protein-rich foods with incidence of early natural menopause in the Nurses' Health Study II cohort. Women included in analyses (n = 85,682) were premenopausal at baseline (1991) and followed until 2011 for onset of natural menopause. Protein intake was assessed via food frequency questionnaire. In Cox proportional hazard models that were adjusted for age, smoking, body mass index, and other factors, women in the highest quintile of cumulatively averaged vegetable protein intake (median, 6.5% of calories) had a significant 16% lower risk of early menopause compared with women in the lowest quintile (3.9% of calories; 95% confidence interval: 0.73, 0.98; P for trend = 0.02). Intake of specific foods, including pasta, dark bread, and cold cereal, was also associated with lower risk (P < 0.05). Conversely, animal protein intake was unrelated to risk. High consumption of vegetable protein, equivalent to 3-4 servings per day of protein-rich foods, is associated with lower incidence of early menopause in US women.