Are you most alert at sunrise, or do you hit your stride when the world is winding down? New research shows that whether you are an early riser or a night owl is more than a matter of habit, it is rooted in biology.

“Chronotype, or circadian preference, refers to a person’s preferred timing of sleep and waking and is partly genetically determined so it may be difficult to change,” said Tianyi Huang of Brigham and Women’s Hospital.

Scientists say our bodies run on internal clocks that place us on a spectrum from early birds to night owls. Early birds tend to fall asleep and wake earlier, hitting an energy peak in the morning. Studies have shown that those who prefer mornings are often healthier and have stronger social circles. Age also nudges the clock, with adolescents preferring to stay up later before drifting to earlier waking times in adulthood.

Night owls naturally stay up and wake later, with energy peaking in the afternoon or evening. Forcing that pattern into daytime routines can be tough. In a study of over 60 000 nurses in the United States, people who preferred to go to bed later carried higher diabetes risk, much of it explained by lifestyle, yet a residual risk remained after adjustment. Being a night owl has also been linked to other health issues such as depression.

Early birds get not only the worm but also have better health outcomes.