The midpoint of sleep is associated with dietary intake and dietary behavior among young Japanese women.

Objectives: How human chronotype is correlated to nutrient and food-group intakes and dietary behavior remains to be elucidated. We cross-sectionally examined the association between the midpoint of sleep and these dietary variables in young Japanese women. A calculated halfway point between bedtime and rise time was used as midpoint of sleep.

Methods: The subjects were 3304 female Japanese dietetics students aged 18-20years from 53 institutions in Japan. Dietary intake during the previous month was assessed by a validated, self-administered diet history questionnaire. The midpoint of sleep was calculated using self-reported bedtimes and rise times.

Results: Late midpoint of sleep was significantly negatively associated with the percentage of energy from protein and carbohydrates, and the energy-adjusted intake of cholesterol, potassium, calcium, magnesium, iron, zinc, vitamin A, vitamin D, thiamin, riboflavin, vitamin B(6), folate, rice, vegetables, pulses, eggs, and milk and milk products. It was also significantly positively associated with the percentage of energy from alcohol and fat, and the energy-adjusted intake of noodles, confections, fat and oil, and meat. Furthermore, subjects with a later midpoint of sleep tended to begin meals later, eat for a longer time, skip meals more frequently, and watch TV at meals, not only at breakfast but also at lunch and dinner.

Conclusions: The midpoint of sleep is significantly associated with dietary intake of certain nutrients and foods and other dietary behaviors in young Japanese women. This finding may contribute to consider the relationships between chronotype and dietary intakes and behaviors.