Some people wake up early like clockwork with a chipper attitude and are eager to start the day. Then there those who have a bit of a slower start, but stay up till the wee hours claiming they’re most productive at night. Sound familiar?

It turns out those waking habits may be embedded in our genes, and scientists have divided them into two categories: “lark” genes in morning people, and “owl” genes in night people.

A team of Mass General researchers, led by Richa Saxena, PhD, in partnership with researchers from the University of Exeter Medical School, published a study in Nature Communications that uncovered more genetic links to circadian rhythms and waking time. They found that people with lark genes may have lower rates of depression when compared to people with owl genes.

What is Your Circadian Rhythm?

Circadian rhythm is a vital cycle that occurs in most living organisms, and it affects number of biological and behavioral processes within the body such as hormonal changes, body temperature and sleeping patterns. Certain genes linked to circadian rhythm have also been tied to certain metabolic and psychiatric disorders.

What the Research Team Found

To gain a deeper understanding of how our genes relate to circadian rhythms and health, Mass General and Exeter researchers used analyzed the genomes of almost 700,000 people from the UK Biobank and 23andMe.

The researchers compared lark and owl gene variants to waking times recorded using activity monitor data from the UK Biobank and a self-reported survey of sleeping and wakeup times. Their analysis increased the number of known loci (the areas of a chromosome where specific genes are found) over tenfold, from 24 to 351.

They found that a number of genes affect what time a person sleeps and wakes up, with the waking times of those with the most lark alleles (gene variants associated with early rising) being shifted an average of 25 minutes earlier than those with the fewest. But investigators also found correlations between these genes and the presence of psychiatric traits.

Connections to Schizophrenia and Depression

The most genetically correlated trait was overall subjective wellbeing, which was positively associated with being a morning person and having lark genes. Being a morning person was also negatively associated with psychiatric traits for disorders like schizophrenia and major depressive disorder.

This means that morning people tend to be happier and have a lower likelihood of experiencing schizophrenia and depression, relatively speaking.

Genetic insights are not always black and white, however, and the results cannot establish a causal relationship. For example, individuals with schizophrenia may tend to go to be later than healthy individuals, but that does not mean their condition is caused by their sleep habits.

But researchers are hopeful studies like these can provide insight into circadian biology and its links to human disease.

“This study highlights the power of teamwork and large-scale human genetics to reveal new aspects of the biology and health implications of our body clocks. The results will also allow researchers to explore more deeply how living in conflict with our individual internal time can lead to poorer health and may point to future individualized intervention strategies.”

Richa Saxena, PhD

Richa Saxena, PhD, is an Assistant Investigator in the Center for Genomic Medicine at Massachusetts General Hospital, an Assistant Professor of Anesthesia at Harvard Medical School and a Phyllis and Jerome Lyle Rappaport MGH Research Scholar 2016-2021.

About the Mass General Research Institute
Research at Massachusetts General Hospital is interwoven through more than 30 different departments, centers and institutes. Our research includes fundamental, lab-based science; clinical trials to test new drugs, devices and diagnostic tools; and community and population-based research to improve health outcomes across populations and eliminate disparities in care.
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