Isoflavone Intake Associated with Improved Sleep Duration and Quality
Reviewer: Tori Hudson, N.D.
Author: Cui Y, Niu K, Huang C, et al.
Reference: Relationship between daily isoflavone intake and sleep in Japanese adults: a cross-sectional study. Nutr J. December 29, 2015;14:127.
Design: Data was collected from a prospective cohort study of risk factors of chronic disease among adult workers in Japan that included annual health exams, blood tests, a self-administered diet history questionnaire, sleep questionnaire and a self-rating depression measure. A total of 1076 individuals met the criteria for analysis.
Monthly intake of 75 food items and serving sizes were quantified. Isoflavone intake was mainly from soybeans. The typical intake was taken from three soy foods with high isoflavones including natto, tofu and dried tofu. Frequency of consumption was recorded in categories from almost never to 2 or more times per day, for each food that was eaten in the month before their health exam.
The mean daily consumption of nutrients was calculated for all nutrients. Daily isoflavone intake was summarized in quartiles: Quartile 1, 0-10.96 mg/1000 kcal/day; Quartile 2, 10.97-17.99 mg/1000 kcal/day; Quartile 3, 18.00-26.73 mg/1000 kcal/day; Quartile 4, 26.74-83.06 mg/1000 kcal/day.
Sleep duration was categorized as either less than 7 hours/night or 8 or more hours/night. Sleep quality was assessed with a standard sleep questionnaire and participants answered yes or no to the question of whether or not they felt refreshed after sleep.
Other information gathered included blood pressure, fasting blood glucose, serum triglycerides, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol. Body mass index (BMI) and daily physical activity were also recorded for each participant. Intake of alcohol, tobacco, hypnotic drugs, education level, coffee and select vitamins.
Participants: Of 1076 participants, (827 were men), 143 (13.3%) had normal sleep duration and 605 (56.2%) were categorized as having sufficient sleep quality.
Primary outcome: Primary outcomes was the relationship between isoflavone intake and sleep duration and sleep quality.
Key findings: Sleep duration rose with higher isoflavone intake as follows: 1.00 (Q1); 0.93 (Q2)1.12 (Q3) and 1.64 (Q4). Higher isoflavone intake was associated with improved sleep quality: 1.00 (Q1); 1.33 (Q2); 1.52 (Q3); and 1.91 (Q4). These study findings indicate that high daily isoflavone intake from foods is significantly associated with optimal sleep length (7-8 h/d) and sleep quality. This association exists when factoring in other variables in diet and lifestyle.
The mechanism of action of this association between higher intakes of dietary isoflavones and improving sleep duration and quality is not known. However, it appears possible that the interaction of isoflavones with estrogen receptors might be involved. Estrogen affects neurotransmitters that regulate sleep, therefore it seems possible that a phytoestrogen might also affect these same neurotransmitters. Unfortunately, this study was shy in women, both premenopausal and postmenopausal. It also is limited by its design and self-administered diet questionnaires. Given the significant prevalence of sleep disorders and the association of sleep problems with higher risk of coronary artery disease, hypertension, diabetes and obesity… I’m always interested in new options.