You have certainly heard of the terms “early riser” and “night owl”, but what you may not know is that scientists have developed a way to measure exactly who you are and even more accurately how late it is in your body compared to the rest of the world.
The internal 24-hour clock in your brain is known as your daily rhythm, and its personal manifestation is your chronotype – which is very different for each individual.
For example, night owls tend to have a late chronotype; these individuals have a delay of any number of hours in their daily rhythm, go to bed late and wake up late. Similarly, those whose internal clock is advanced have an early chronotype and tend to be early risers.
Recently, scientists have developed a blood test to determine how delayed or advanced the internal clock is in relation to external time.
Three laboratories have researched techniques to do just that. All have the same basic approach, namely measuring changes in RNA levels in blood cells. This gives us an idea of which genes are expressed and to what extent, and which are not. This information can then be used to determine where in their 24-hour cycle a person falls at the time of the test, essentially indicating their internal or biological time.
At Northwestern University, Dr. Rosemary Braun developed “TimeSignature”, a test that determines the expression of 40 different genes from two blood samples. Why these 40? During the development of the test, the Braun team used data from blood samples taken from volunteers every 2 hours to find patterns for variation in gene expression over the course of the day. They first measured the expression of about 20,000 different genes.
They then ran these data through a machine learning algorithm to determine which genes had expression patterns that best predicted the time of day, and these 40 genes were identified as the result. The method can predict a person’s biological time with reasonable accuracy within 1.5 hours.
How could this test be useful? Since our internal clock regulates the function of all our major organs, each of which has its own daily rhythm, it may be possible to better determine the best time to administer certain drugs or treatments. One notable example is that administering 5-fluorouracil, a type of chemotherapy, in the middle of the night to patients with gastrointestinal cancer increases toxicity fivefold. Another reason is that open-heart surgery performed in the afternoon instead of in the morning halves the risk of complications.
One study also found that angiotensin-2 receptor blockers were more effective in reducing the complications of cardiovascular disease in people with hypertension when taken at bedtime than when taken in the morning. This type of treatment plan is called chronotherapy. Knowing if a person’s internal clock is delayed or brought forward can further improve the precise timing of this and other treatments to maximize the benefits and minimize the risks.
In addition, abnormalities at the time of the circadian cycle have been associated with a variety of conditions, such as depression, diabetes, heart disease and Alzheimer’s disease. It is important to investigate whether this difference in their internal time contributes to the symptoms of these disorders. Knowing whether these patients have a circadian phase advance or delay in addition to these conditions can therefore be helpful in treatment.
There is also a class of sleep disorders known as circadian rhythm disturbances, which include a disturbance of the sleep-wake cycle. Delayed phase sleep disorders and advanced phase sleep disorders are two of them and occur when significant phase advances or delays impair quality of life. This category also includes shift work disorder, which occurs in people whose work falls at the exact time when their body would tend to sleep. Circadian rhythm disturbances can lead to excessive drowsiness, insomnia, attention and mood difficulties, and several negative long-term effects. This blood test could be ideal for diagnosing and treating such disorders by knowing the timing of the circadian cycle and how it is altered in these patients.
It is also a known fact that sleep changes with age. With age, it takes longer to fall asleep and sleep becomes more fragmented. The increased need for bathroom excursions during the night, which is associated with ageing, and a general lowering of the threshold for awakening contribute to sleep fragmentation. In addition, sleep architecture, i.e. the organization of sleep into different phases, shows some changes. Older people spend less time in less of these phases: slow sleep and REM sleep. These and other factors lead to a shorter total sleep duration during the night.
It is important to note that there is also a remarkable phase progression in ageing, which means that despite all efforts, people tend to become sleepy much earlier in the day and wake up much earlier too, with the inability to sleep in the morning after a certain amount of time. This shift in the daily rhythm can sometimes have undesirable consequences, such as a general lack of sleep. Knowing the circadian phase of the elderly can provide information on how to help people whose quality of life has been affected by these changes.
Overall, the timing of circadian rhythms varies greatly between individuals. As we work to develop more individualized treatments, this tool can make a significant contribution to diagnosing, understanding and treating a wide range of conditions. All this shows that the body’s internal clock can be as important as the time you see when you look at your watch.