A study measuring the sleep patterns of students found that students fell asleep later in the evening and woke up later in the morning during winter. Students also received less natural light exposure during the winter, when daylight hours on the campus are limited and the skies are notoriously overcast. The researchers believe this lack of daytime light exposure triggered the delayed winter bedtimes by 'pushing back' (or delaying) their natural circadian cycle. Getting outside in the morning, even on cloudy days, is the best way to prevent this circadian delay, they say.
