A study in the journal Sleep looked at the sleep and awake times of 2,200 Australian teens and preteens.
The children who went to bed late and woke up late got the same amount of time as the early birds. Yet their sleep patterns exposed them to more unhealthy behaviors.
Researchers observed that early-bed/early-risers slept 70 to 90 minutes earlier and in the morning woke up about an hour to an hour and a half earlier than the late risers.
On average, the late risers had a higher body mass and index and were more likely to be obese and overweight. The reason: sleeping late led to more sitting and less exercise.
The early risers were able to accumulate about 27 more minutes of physical activity and vigorous exercise.
The late risers spent 48 more minutes online and watching TV, and this usually happened between the hours of 7 p.m. and midnight.
On a broad scale, researchers say late risers basically exchanged 30 minutes of physical activity for 30 minutes of sedentary behavior.
This is a key finding since all the research shows a large number of teens tend to stay up late and wake up late, and these are habits kids often carry on as adults.