Association of Frequency of Milk or Dairy Product Consumption with Subjective Sleep Quality during Training Periods in Japanese Elite Athletes: A Cross-Sectional Study.

The purpose of the study was to examine the association of the frequencies of milk and dairy product consumption with subjective sleep quality during the training period in Japanese elite athletes. In this cross-sectional study, 682 Japanese elite athletes who were candidates for the 2016 Rio Olympic Games underwent medical evaluations at the medical center of The Japan Institute of Sports Sciences. Self-reported questionnaires were used to collect information on demographics and lifestyle (age, height, weight, sports, presence of milk allergy, smoking and drinking habits), subjective sleep quality (good, normal, or poor), bedtime, waking time, sleep duration, and frequencies of milk and dairy product consumption. Data from 679 athletes (379 men, 300 women) without milk allergy, were analyzed. Based on the frequencies of both milk and dairy product consumption, the athletes were divided into three groups: low (0-2 d/wk), middle (3-5 d/wk), and high (6-7 d/wk). Multiple logistic regression models showed that in comparison with the low milk consumption group, the middle [OR (95% CI): 0.48 (0.26-0.91)] and high groups [0.38 (0.21-0.71)] were significantly associated with a lower risk of decrease in subjective sleep quality (0: good, 1: normal or poor) only in women, after adjusting for possible confounders, such as smoking, drinking habits, and sleep duration. Accordingly, the present study elucidated that a greater frequency of milk consumption was significantly associated with a lower risk of decrease in subjective sleep quality, during training periods in women.