Are You a Lion, Bear, Wolf, or Dolphin? Understanding Your Chronotype

The four chronotypes (lion, bear, wolf, dolphin) as described in a TODAY article, and what the cited studies found about age, genetics, light and mortality.

By Harry Soul - SleepWiseReviews

Independent Sleep Researcher - September 2022

The Four Chronotypes

The four-type model below is sleep doctor Michael Breus's, as described in a TODAY article. Treat the types as a starting point for thinking about your schedule, not a clinical diagnosis.

Lion (about 15-20% of people, per Breus via TODAY)

Early risers who are up at the crack of dawn. Most productive in the morning.

Bear (about 50% of people, per TODAY)

Bears usually follow the schedule of society, with sleep-wake patterns matching the solar cycle. They like to get their seven or eight hours of sleep. Most people, according to the article, fall into the bear category.

Wolf (about 15-20% of people, per TODAY)

Self-proclaimed night owls. They have a hard time waking up early and are most energetic in the evenings. The article says wolves can plan to be most productive at night.

Dolphin (about 10% of people, per TODAY)

Light sleepers who, according to the article, struggle the most with insomnia. They tend to wake up feeling unrefreshed.

Working With Your Chronotype

If you tend to run late and have an early schedule, remember that light and dark have the biggest influence on circadian rhythms (see the NIGMS note below).

What Researchers Mean by Chronotype

The National Institute of General Medical Sciences describes circadian rhythms as including some of the physical, mental and behavioral changes an organism experiences over a 24-hour cycle, and says light and dark have the biggest influence on them.

Roenneberg and colleagues (2007) report that sleep and wake times show a near-Gaussian distribution in a given population. They also report that chronotype is both age- and sex-dependent. A Healthline overview puts it this way: most research breaks chronotypes into morning, evening and neither, and the majority of people are neither morning nor evening types. The same overview says some describe four types, with the names bear, wolf, lion and dolphin.

The percentages next to the Lion, Bear, Wolf and Dolphin headings come from a TODAY article about Breus's system. The article says that, according to Breus, about 15 to 20 percent of people are lions. It also gives about 50 percent for bears, about 15 to 20 percent for wolves and 10 percent for dolphins, without attributing those figures to him.

How Chronotype Changes With Age

A study of chronotypes in the US observed a near-normal distribution overall and within each age group. Timing shifted later during adolescence, peaking in lateness at about 19 years, and shifted earlier thereafter. The study also found that men are typically later chronotypes than women before 40, but earlier types after 40. For teenagers specifically, see Teen Sleep: Why Teenagers Physically Cannot Sleep Early.

How Much Is Genetic?

A 2019 genome-wide study of 697,828 people in Nature Communications raised the number of genetic locations associated with being a morning person from 24 to 351. In the subset of about 85,000 people with activity-monitor data, those carrying the most morningness alleles (the top 5%) had a mean sleep timing 25 minutes earlier than the 5% carrying the fewest. The authors estimated the heritability of chronotype from the genetic data at 13.7%, towards the lower end of previously reported figures (12 to 21%). For more on the genetics of sleep timing and duration, see Morning Larks vs Night Owls: Is Your Sleep Type Actually Genetic?

Can Light Shift Your Timing?

In a camping study by Wright and colleagues (2013) volunteers lived under the natural summer light-dark cycle. The abstract reports that later chronotypes showed larger circadian advances when exposed to only natural light. The abstract does not give the size of the shift. See Light Therapy for Sleep: How to Use It and When It Helps for practical options.

Evening Types, Health and Schedules

In UK Biobank data, Knutson and von Schantz (2018) found that, compared with definite morning types, definite evening types had significantly increased risk of all-cause mortality (HR 1.10, 95% CI 1.02-1.18). The authors say mortality risk in evening types may be due to behavioral, psychological and physiological risk factors. Roenneberg's 2012 work on social jet lag reports that the discrepancy between circadian and social clocks is associated with increased body mass index. If your schedule is irregular as well, Sleep Consistency and Health: What the Research Shows is a useful next read.

What the Research Shows

• It shows that sleep timing follows a near-Gaussian distribution differs by age and sex, and has a genetic component.
• A 2019 genome-wide study estimated the heritability of chronotype at 13.7% from genetic data, and light exposure shifted timing in one study.
• In one cohort, definite evening types had significantly increased risk of all-cause mortality (HR 1.10).

When To Talk to a Clinician

For insomnia, the NHS insomnia page advises seeing a GP if you have had trouble sleeping for months, or if it is affecting your daily life in a way that makes it hard for you to cope.