Is Exercise Effective at Improving Blood Glucose in Diabetes?
By Dr Roxie Becker

In the case of type 2 diabetes, there is usually a large emphasis placed on dietary changes, which can be very effective. However, it is also important to counsel patients on exercise which can further improve blood glucose control.

Glucose uptake during exercise

Glucose is transported into the muscle during exercise through insulin-mediated and insulin-independent pathways. One of the main glucose channels in muscle is the GLUT4 channel. When insulin binds to insulin receptors on the cell surface, it causes these GLUT4 channels to be inserted into the cell membranes, which allows glucose into the cell.

In the case of type 2 diabetes, there is impaired signaling inside the cells, which prevents these GLUT4 channels from being inserted into the membranes in response to insulin. Exercise improves insulin sensitivity and causes these channels to be inserted into cell membranes, independent of insulin, which is why it can be especially effective for blood glucose control in people with insulin resistance.

Exercise improves insulin sensitivity

Exercise has been shown to improve insulin sensitivity for up to 72 hours after an acute bout of exercise.¹ Short-term studies using continuous glucose monitors (CGMs) have shown that regular exercise is effective at reducing average blood glucose levels and at reducing the time spent in hyperglycemia each day (blood glucose levels of greater than 10.0 mmol/dL).² The meta-analysis also showed that regular exercise did not significantly increase the risk of hypoglycemia (low blood glucose levels).

How much and what types of exercise are effective?

General physical activity recommendations include 150 minutes of moderate to vigorous activity per week. People who meet or fall short of this recommendation lower their HbA1c by an average of 0.36% points, while people who obtain more than 150 minutes per week lower their HbA1c by an average of 0.89% points.³ Given that the improved insulin sensitivity in response to exercise persists for only around 48-72 hours, it has been suggested that exercising at least every 48 hours is likely to be more beneficial for long-term glycemic control rather than longer bouts of exercise less frequently.¹

Regarding the type of exercise, one randomized clinical trial allocated people to either do aerobic training, resistance training, or both for 22 weeks. While all types of exercise improved HbA1c, the group that included both types of exercise (for the same total weekly exercise minutes as the other groups) saw significantly greater improvements in their HbA1c.⁴

While more seems to be better, it’s also important to meet people where they are, and any amount of exercise is beneficial. Timing may also play an important role. One randomized trial compared advising people to either walk for 30 minutes a day in total, or to specifically walk for just 10 minutes after breakfast, lunch, and supper.⁵ When people walked after meals, their blood glucose levels improved significantly more than when they walked during other times of the day.

The effects of exercise on diabetes-related complications

Since the complications of diabetes result from blood vessels being exposed to elevated blood sugar levels over time, these effects are likely to reduce diabetes-related vascular complications. A meta-analysis published in 2022 found that higher amounts of exercise were associated with lower risks of cardiovascular disease, cardiovascular mortality, and microvascular complications such as retinopathy (resulting from damage to the blood vessels in the back of the eye) and peripheral nephropathy (damage to the nerves in the feet and hands).⁶ These outcomes results should make prescribing exercise to people with diabetes a non-negotiable.

A word of caution

According to the American Diabetes Association, there is no evidence to suggest that individuals with diabetes need to be extensively screened (such as a cardiac stress test) if they want to participate in low-intensity exercise such as walking.⁷ However, for sedentary and older individuals who wish to engage in more vigorous activity, they should be screened for complications that could predispose them to injury when undertaking a new exercise program. These include, but are not limited to, coronary artery disease, severe peripheral neuropathy, severe autonomic neuropathy (damage to the nerves that regulate blood pressure and other central nervous system functions), and proliferative retinopathy.

Individuals taking injectable insulin should also be cautioned to carefully monitor their blood sugar levels during exercise and should be made aware of the symptoms of hypoglycemia and educated to keep glucose tablets or fruit juice nearby. This is because those taking injectable insulin are at a higher risk of hypoglycemia during acute bouts of exercise. In individuals who are managing their diabetes with lifestyle changes alone are at minimal risk of hypoglycemia, but should still be warned about the symptoms to be aware of.

In conclusion, exercise forms an important part of a lifestyle approach to the management of type 2 diabetes, and can effectively improve glycemic control and reduce the risk of diabetes-related complications.

References:

1. Way KL, Hackett DA, Baker MK, Johnson NA. The Effect of Regular Exercise on Insulin Sensitivity in Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis. Diabetes Metab J. 2016 Aug;40(4):253-71. doi:10.4093/dmj.2016.40.4.253
2. MacLeod SF, Terada T, Chahal BS, Boulé NG. Exercise lowers postprandial glucose but not fasting glucose in type 2 diabetes: a meta-analysis of studies using continuous glucose monitoring. Diabetes Metab Res Rev. 2013 Nov;29(8):593-603. doi:10.1002/dmrr.2461
3. Umpierre D, Ribeiro PAB, Kramer CK, et al. Physical Activity Advice Only or Structured Exercise Training and Association With HbA1c Levels in Type 2 Diabetes: A Systematic Review and Meta-analysis. JAMA. 2011;305(17):1790–1799. doi:10.1001/jama.2011.576
4. Sigal RJ, Kenny GP, Boulé NG, Wells GA, Prud’homme D, Fortier M, Reid RD, Tulloch H, Coyle D, Phillips P, Jennings A, Jaffey J. Effects of aerobic training, resistance training, or both on glycemic control in type 2 diabetes: a randomized trial. Ann Intern Med. 2007 Sep 18;147(6):357-69. doi:10.7326/0003-4819-147-6-200709180-00005
5. Reynolds AN, Mann JI, Williams S, Venn BJ. Advice to walk after meals is more effective for lowering postprandial glycaemia in type 2 diabetes mellitus than advice that does not specify timing: a randomised crossover study. Diabetologia. 2016 Dec;59(12):2572-2578. doi:10.1007/s00125-016-4085-2
6. Marlene Rietz, Alexander Lehr, Eriselda Mino, Alexander Lang, Edyta Szczerba, Tim Schiemann, Christian Herder, Nina Saatmann, Wolfgang Geidl, Janett Barbaresko, Manuela Neuenschwander, Sabrina Schlesinger; Physical Activity and Risk of Major Diabetes-Related Complications in Individuals With Diabetes: A Systematic Review and Meta-Analysis of Observational Studies. Diabetes Care. 2022; 45 (12): 3101–3111. doi:10.2337/dc22-0886
7. Colberg SR, Albright AL, Blissmer BJ, Braun B, Chasan-Taber L, Fernhall B, Regensteiner JG, Rubin RR, Sigal RJ; American College of Sports Medicine; American Diabetes Association. Exercise and type 2 diabetes: American College of Sports Medicine and the American Diabetes Association: joint position statement. Exercise and type 2 diabetes. Med Sci Sports Exerc. 2010 Dec;42(12):2282-303. doi:10.1249/MSS.0b013e3181eeb61c