Relationship between daily isoflavone intake and sleep in Japanese adults: a cross-sectional study

Background: Isoflavones comprise a class of phytoestrogens that resemble human estrogen in chemical structure, and have weak estrogenic effects. Because estrogen modulates sleep duration and quality, we hypothesized that isoflavones would have a beneficial effect on sleep status in a way similar to estrogen. We conducted a cross-sectional study to investigate the relationship between daily isoflavone intake and sleep status in Japanese subjects. Methods: Our study included 1076 Japanese adults aged 20-78 years. Daily isoflavone intake was assessed using a brief self-administered diet history questionnaire, and sleep was evaluated using a self-reported questionnaire. Results: The prevalence of regular sleep duration (7-8 h/day) and sufficient sleep quality were 13.3 % and 56.2 %, respectively. After adjusting for potential confounding factors, the odds ratios (95 % CIs) for optimal sleep duration (7-8 h) when higher isoflavone intakes (Q2-Q4) were compared with low isoflavone intake (Q1) were Q2: 0.94 (0.53-1.56); Q3: 1.28 (0.73-2.24); and Q4: 1.84 (1.06-3.18) (p for trend = 0.013). In the final adjusted model, sufficient sleep quality across categories of isoflavone intake was Q1: 1.00 (reference); Q2: 1.30 (0.91-1.84); Q3: 1.48 (1.03-2.12); and Q4: 1.78 (1.22-2.60); (p for trend = 0.002). Conclusion: Higher daily isoflavone intake was positively associated with optimal sleep duration and quality in a Japanese population. This finding suggests that daily isoflavone intake may have a potentially beneficial effect on sleep status.