Your circadian rhythm is the 24-hour clock that drives wakefulness and sleep. Disruptions to this biological clock have profound effects on our bodies and our hormones. New research has identified genes for the biological clock, known as clock genes, which may be the basis for metabolic diseases like obesity, diabetes and insulin resistance. The biological clock has a powerful influence on metabolism and appetite. When someone’s circadian rhythms are out of whack—by dysfunctional genes or by not getting enough sleep, jet lag or eating at unusual times, metabolism slows down and appetite increases.
Traditionally, the brain has been thought to be the main controller of our circadian clock. We now know that different organs in the body like the pancreas, liver and the intestines all have their own circadian rhythms. Each organ produces hormones, enzymes and other molecules at various times of the day. The brain acts more like a conductor of the symphony, coordinating the various organs. Metabolic disorders occur when the brain is not in sync with the organs. Insulin resistance is the classic example of this, when the pancreas is out of sync with the liver and the brain, causing insulin production to be too high or too low.
The discovery of clock genes has led to questions about how disruptions in circadian rhythm can contribute to metabolic disease, and if fixing dysfunctional rhythms could help treat conditions like diabetes and obesity. For example, studies are underway to determine if there is an ideal time of day to eat to help with weight loss and blood sugar control.
It is difficult to reverse the effects of metabolic disease once the wheels are set in motion. Researchers have focused on the body’s internal clock to look for ways to treat metabolic derangements. The idea is to find out if a dysfunctional biological clock is the cause or the result of metabolic problems. It’s the classic “chick-and-egg” scenario.
Evidence for the clock: Researchers know that metabolism and the biological clock are connected. Studies have noted variations in genes that control the biological clock in patients with obesity, diabetes and hypertension. In mice, mutations of the clock gene and other genes related to the biological clock cause insulin resistance and metabolic syndrome.
Evidence for the diseases: Some studies have shown that blood sugar other hormones can influence our circadian rhythms.
What comes first? Do metabolic problems precede a dysfunctional biological clock or vice versa?
Dr. Hitoshi Ando, professor at Jichi Medical University in Japan has set out to answer this question. Dr. Ando is studying mice that are genetically deficient in the fat hormone, leptin and are susceptible to obesity and diabetes. It turns out that these mice have defective circadian rhythms. Dr. Ando fed one group of mice a healthy diet and the other group a high calorie diet for one month. The healthy diet only partially corrected the circadian rhythm problem. Next he tried giving leptin injections to the mice, which also had only a partial effect. The conclusion was that a healthy diet and replacing the missing hormone only partially reversed the defective biological clock and that inherent defects in the biological clock have a detrimental effect on hormones. Dr. Ando concluded that the problems in the biological clock were not caused by metabolic abnormalities, but that treatment with leptin and a healthy diet can partially reverse the abnormality.
Other research has shown that a high fat diet disrupts the biological clock. It is thought that leptin plays an important role in maintaining circadian rhythms.
The link between metabolic disease and the circadian clock is especially important for people who work at night and sleep during the day. Studies have shown that people who work these hours are at increased risk for metabolic disease like type 2 diabetes, metabolic syndrome and obesity. Dr. Ando found that working the night shift influences the biological clock as well as leptin.
As we learn more about the influence of circadian rhythms and hormones, it becomes clear that a normal sleep-wake cycle is vital for a healthy body and hormonal balance.