A Person's Internal Clock is Revealed in Hair Roots

Creatures on earth are attuned to the daily cycle of the planet through circadian rhythms: functions that follow a daily, 24 hour pattern. In humans, the central circadian clock sits in the suprachiasmatic nucleus of the hypothalamus, where it can also receive input about the amount of light or darkness the retina is sensing. But there can also be variations in the circadian rhythms from one individual to another; these manifest as preferences to be more (or less) active at certain times of the day.

Now researchers have found a way to determine these natural preferences, also known as the chronotype of an individual, by analyzing their hair roots. Since circadian rhythms can go beyond bodily functions like sleep or metabolism to also influence the effect of medications, this work is meant to serve as a basis for personalized medicine that has been tailored to a person’s chronotype. The study, which analyzed circadian rhythms in around 4,000 people, also determined that rhythms vary slightly in men and women, and that lifestyle choices can impact chornotype more significantly than we knew. The findings have been reported in the Proceedings of the National Academy of Sciences (PNAS).

Before this, melatonin levels in saliva have been the primary way to determine an individual’s personal chronotype. But this is a difficult method that cannot be applied widely, noted senior study author Professor Achim Kramer, head of the Division of Chronobiology at Charité – Universitätsmedizin Berlin.

In this work, the investigators created a method to assess the activity of seventeen genes that are related to circadian rhythm and determine chronotype using hair root analysis. When compared to previous tools, this new approach is comparable.

“Hair analysis is, however, far easier to perform, which is what makes the method so valuable,” noted Kramer. 

A variety of things were found to influence the circadian clock to create the individual chronotype. People who were in their mid-20s tend to get tired later than people who are older than 50. Women tended to have a slightly earlier start of nighttime than men. Unemployed people tended to be more active around 30 minutes later than people who were employed. Genetics also had an influence.

Now the team is doing additional work to standardize the test for widespread use.

Sources: Charité – Universitätsmedizin Berlin, Proceedings of the National Academy of Sciences (PNAS)