Does exercise lower blood sugar levels in patients with diabetes or prediabetes?

Does Exercise Lower Blood Sugar Levels?

Yes, exercise consistently lowers blood glucose levels in people with diabetes and prediabetes through increased muscle glucose uptake and improved insulin sensitivity. 1

Mechanism and Acute Effects

Exercise causes blood glucose to decline through direct mechanisms:

• Muscle glucose uptake increases 7 to 20 times above baseline during physical activity, depending on exercise intensity, independent of insulin action. 2
• Activities of longer duration and lower intensity generally cause a decline in blood glucose levels in both type 1 and type 2 diabetes, though typically not to hypoglycemic levels in those controlled by lifestyle alone. 1, 3
• Moderate exercise (such as walking after meals) lowers maternal blood glucose levels even in gestational diabetes. 1
• The glucose-lowering effect persists for hours after exercise due to enhanced insulin sensitivity, facilitating more efficient glucose disposal when carbohydrates are consumed. 3

Type-Specific Responses

Type 2 Diabetes and Prediabetes

• Individuals with type 2 diabetes will likely experience blood glucose reduction during aerobic exercise, even if hyperglycemic after a meal, because endogenous insulin levels are higher at that time. 1
• Exercise may be undertaken even with blood glucose exceeding 300 mg/dL (16.7 mmol/L) without ketosis, provided the person feels well and is adequately hydrated. 1
• Combined aerobic and resistance training improves glycemic control more effectively than either alone, though this may be related to greater total caloric expenditure. 1

Type 1 Diabetes

• Blood glucose responses are more variable in type 1 diabetes due to the complex interplay between exogenous insulin, exercise-induced glucose uptake, and counterregulatory hormones. 4, 5
• Very intense exercise can cause transient blood glucose elevations lasting 1-2 hours due to catecholamine release, though intermittent high-intensity exercise after breakfast still reduces glucose levels overall. 1

Long-Term Metabolic Benefits

Beyond acute glucose lowering:

• Regular exercise training increases insulin sensitivity and improves glucose tolerance in people with impaired glucose tolerance and type 2 diabetes. 6, 7
• Exercise combined with diet or medication produces greater improvements in glycemic control than medication or diet alone in type 2 diabetes. 6, 7
• The insulin-sensitizing effect of exercise decreases within 3 days and disappears after 1 week, necessitating regular ongoing activity. 2

Critical Safety Considerations

Hypoglycemia Risk

• Individuals with diabetes controlled by lifestyle alone face minimal hypoglycemia risk during exercise and do not require stringent glucose monitoring or carbohydrate supplementation. 1, 3
• Those taking insulin or insulin secretagogues (sulfonylureas, meglitinides) are at significant risk for exercise-induced hypoglycemia and require carbohydrate supplementation and/or insulin dose adjustments. 1
• Consume 15 grams of carbohydrate before exercise if pre-exercise glucose is below 100 mg/dL in insulin users, with the exact amount dependent on insulin doses, exercise duration, and intensity. 1
• High-intensity or prolonged glycogen-depleting exercise requires 5-30 grams of carbohydrate during and within 30 minutes after exercise to prevent delayed hypoglycemia. 1

Medication Considerations

• Metformin rarely causes hypoglycemia by itself, but hypoglycemia can occur if you do not eat enough, drink alcohol, or take other blood sugar-lowering medicines. 8
• Insulin doses should be reduced prior to exercise, though some insulin is typically still needed to prevent ketogenesis. 4

Recommended Exercise Prescription

Adults with Diabetes

• Engage in at least 150 minutes per week of moderate-to-vigorous aerobic exercise, spread over at least 3 days with no more than 2 consecutive days without activity. 1
• Perform resistance exercise 2-3 sessions per week on nonconsecutive days to maximize glucose control benefits. 1
• Daily exercise is recommended to decrease insulin resistance, regardless of diabetes type. 1

Youth with Diabetes

• Youth should engage in 60 minutes daily of moderate-to-vigorous aerobic activity, with muscle- and bone-strengthening activities at least 3 days per week. 1

Common Pitfalls to Avoid

• Do not postpone exercise due to elevated glucose (unless >300 mg/dL with ketosis or feeling unwell), as exercise will lower glucose in type 2 diabetes. 1
• Do not assume all diabetic patients need pre-exercise carbohydrates—this applies only to insulin and secretagogue users. 1
• Do not allow more than 2 days between exercise sessions, as insulin sensitivity benefits dissipate rapidly. 1, 2
• Monitor glucose before, during, and especially after exercise in insulin users, as delayed hypoglycemia can occur hours later. 1