Type 2 Diabetes + the Circadian Clock: Does Timing of Exercise Matter?

Coverage of the American Diabetes Association (ADA) Scientific Sessions is brought to you by the ADA x BT1 Collab.

Speakers for this session, “Zeitbergers (Time-keepers) of Metabolic Health–Resetting the Circadian Clock,” included: Joseph (Joe) Bass, MD, Ph.D. (Northwestern University Feinberg School of Medicine), Dongyin Guian, Ph.D. (Baylor College of Medicine), Kristin Eckel-Mahan, Ph.D. (University of Texas Health Science Center), Juleen R. Zierath, Ph.D. (Karolinska Instituet) and Lisa Chow, MD, MS (University of Minnesota).

In this article, we focus on the research presented by Juleen R. Zierath.

Scientists credited throughout her part of the presentation at ADA 2022 included: Paolo Sassone-Corsi, John A. Hawley, Harriet Wallberg-Henriksson, Anna Krook and their respective teams.

Juleen R. Zierath is a biologist who studies the cellular mechanisms that impact insulin resistance. Her team focuses on insulin sensitivity, metabolic levels and how muscles use oxygen throughout the day. They explore how these levels shift in people with diabetes, metabolic impairments, or obesity.

What is the circadian clock?

In one of the studies presented, researchers were interested in understanding how synchronizing exercise and diet to your circadian clock (essentially, the body’s internal clock) may alter genes and metabolism—particularly “Mitochondria convert chemical energy from the food we eat into an energy form that the cell can use.” (Medical News Today)mitochondrial function and glucose metabolism.

A circadian clock or rhythm is “physical, mental and behavioral changes that follow over a 24-hour cycle.” Circadian clocks and rhythms are natural processes that most living things experience.

The impact of exercise on glucose levels

Researchers examined whether exercising at different times of day affects blood sugar levels. Specifically, they were interested to see if certain times of day were associated with less rise in blood sugar levels after exercise. They first analyzed glucose levels throughout the day using a continuous glucose monitor (CGM) in men with type 2 diabetes against a control group.

“Exercise has an insulin-independent effect on glucose metabolism,” Zierath explained.

Results: exercising in the morning vs. afternoon

Researchers found that blood glucose dropped when the men performed exercise training in the afternoon. However, morning exercise was linked to an unexpected rise in blood glucose levels. 

Data from fat and muscle biopsies, serum and plasma samples showed many changes in proteins associated with glucose metabolism when the men participated in high-intensity cycling in the morning. Whereas, when participants exercised in the afternoon, the data showed changes in mitochondrial metabolism. 

Irrespective of the time of day, the training altered many types of “A lipid is any of various organic compounds that are insoluble in water. They include fats, waxes, oils, hormones, and certain components of membranes and function as energy-storage molecules and chemical messengers.” (Britannica)lipids in participants. Training in the morning had a unique effect on the metabolism of carbohydrates.

Timing of exercise matters—even for mice!

Similar studies focused on mice, which gave scientists a good comparison of how exercise and the circadian clock affect animals other than humans. The mice study showed similar results to the one with humans. The mice were trained in early active and rest phases. Though opposite of the human circadian clock, this was still a meaningful comparison.

“When mice were trained at the early active phase, we found changes in metabolism,” Zierath said. 

Ketone metabolism, amino acid breakdown, lipid oxidation and more were affected in mice.

Afternoon exercise: a winner for blood glucose levels

Research consistently showed that afternoon training in people with type 2 diabetes or obesity may better affect glucose metabolism overall. 

Zierath concluded that “timing of exercise during the day may prove to be valuable therapy for patients with metabolic disorders.”

The bottom line is: Diabetes is complicated and affects everyone uniquely. Exercise is just one tool for diabetes management. Consider experimenting if you are interested in timing your exercise around your circadian rhythm. Click here for tips on exercising safely, healthily and positively with type 2 diabetes.