Many diseases have regular daily variations in risk or symptoms tied to the body’s internal clock.
Like others in the modern world, you probably spend a lot of your day living by the clock.
Your body does the same thing with many of its internal functions, except that the clock it uses isn’t on a smartphone.
The body actually has many biological “clocks” that create the body’s circadian rhythms — the physical, mental, and behavioral changes that follow a daily cycle. And now researchers are uncovering how treatment for conditions can be improved with by working with these “clocks.”
There’s a master clock in the hypothalamus in the brain. This is set by the light and dark cycle in your environment. There are also many peripheral clocks composed of molecules in cells throughout the body.
Scientists think that, in general, the circadian system optimizes the functioning of the body. But for people with certain diseases, the circadian system can make symptoms worse at specific times of the day.
Several diseases show regular daily variations in their risk or severity of symptoms.
Colds or infections. One study found that fever peaked in the evening for bacterial infection and in the morning for viral infection.
In another study, nasal secretions during a cold were highest in the early morning, decreased during the day, and increased a little in the evening.
Seasonal allergies. Seasonal allergy symptoms — sneezing, stuffy nose, and red, itchy eyes — are more common in the morning compared to the rest of the day.
Although many diseases follow daily patterns, factors other than circadian rhythms can also play a part.
For example, with nighttime asthma, lying down or sleeping may contribute to a person’s symptoms.
Steven Shea, PhD, a circadian rhythm researcher at Oregon Health and Science University in Portland, said these factors, along with circadian rhythms, “add together to make asthma symptoms even worse for some people during the night.”
“Monday morning is the worst time for heart attacks because it’s also the first day of the workweek back at work,” said Courtney M. Peterson, PhD, an assistant professor of nutrition at the University of Alabama at Birmingham’s Nutrition Obesity Research Center.
“This is an example of a combined effect due to the circadian rhythm, or biological clock, and behavior or what’s going on with your life,” said Peterson.
Shea’s lab runs controlled studies to further understand how circadian rhythms contribute to daily disease patterns.
Epinephrine plays an important role in the cardiovascular system’s response to stress. It causes a number of physiological changes, such as increased heart rate and blood pressure, and more rapid breathing.
“We’re now looking at people with sleep apnea and asking them to exercise at different times of day and night in the lab,” said Shea, “looking at their physiological responses to different challenges at different times.”
Understanding how circadian rhythms affect disease severity can also help doctors treat diseases more effectively — what’s known as chronotherapy.
Some of this has to do with timing medications to match the circadian rhythms.
“By doing this, you could reduce the side effects and the cost of the drugs,” said Shea, “but you may also improve the efficacy.”
Another approach is to give people vaccinations when their immune system is most likely to produce a beneficial immune response.
The timing of medications and vaccinations is only one type of chronotherapy.
Peterson studies how shifting when you eat affects health.
“There’s more and more evidence that the time of day that you eat has an effect on health,” said Peterson.
In one study, she put men with prediabetes on either a 12-hour or 6-hour feeding schedule. Men on the shorter schedule — known as time-restricted feeding — finished dinner by 3 p.m. each day.
This study combined both eating according to circadian rhythms and intermittent fasting, so it’s difficult to know the circadian effects alone.
But Peterson said that other research has found that eating more of your daily calories for breakfast and lunch — even without changing the time of meals — improves blood sugar control and other risk factors for obesity and type 2 diabetes.
This dietary research is still in its early stages, with no large clinical trials yet. But as larger studies are done, the effects of mealtime on health will become more clear.
“I expect in the next 10 years that we’ll probably have clear national dietary guidelines on meal timing,” said Peterson.
Researchers are learning more about how your circadian rhythms affect your overall health. The body has many biological “clocks” that create the body’s circadian rhythms — the physical, mental, and behavioral changes that follow a daily cycle.
Researchers are hoping to discover ways people can stay healthy by harnessing their circadian rhythms.