Blood Sugar and Exercise
How exercise affects blood sugar and diabetes.
- Total Diabetes Wellness
- Updated on February 18, 2024
- Science Based
Exercise is an essential part of managing diabetes. Whether you have prediabetes, type 1 diabetes, or type 2 diabetes, regular exercise will improve your overall health and help stabilize and lower your blood sugar levels.
People with diabetes must be careful about their blood sugar levels when exercising. Too much or too little exercise can cause blood sugar spikes and dips, which can be dangerous. But with a little knowledge and planning, it is possible to enjoy safe and healthy exercise while managing your diabetes.
Always discuss exercise with your doctor BEFORE starting any kind of exercise program. This is especially important if you are on medications. Full disclaimer here.
The Effect of Exercise on Blood Sugar
Exercise can have both short-term and long-term effects on blood sugar levels. In the short term, exercise can cause blood sugar levels to rise or fall, depending on the type of exercise, the intensity, and how long you exercise. In the long term, regular exercise can help improve your body’s sensitivity to insulin, which can help keep your blood sugar levels in a healthy range.
The type of exercise you do can affect your blood sugar levels differently. Aerobic exercise (such as walking, running, or cycling) can cause your blood sugar levels to rise during and for hours after exercise. This is because when you do aerobic exercise, your muscles use more glucose for energy. The release of stored glucose for energy means blood sugar levels rise, and your body needs to release more insulin to balance your blood sugar levels.
If you have diabetes and are insulin resistant (pre-diabetes or type 2 diabetes) or your body doesn’t make insulin (type 1 diabetes or LADA), your blood sugar levels may remain high after exercise. Usually, your blood sugar levels will come down on their own shortly after exercise. However, people with type 1 diabetes may need to take additional insulin to lower blood sugar levels.
Anaerobic exercise (such as weightlifting or sprinting) can cause your blood sugar levels to fall during and for up to 24 hours after exercise. This is because when you do anaerobic exercise, your muscles use less glucose for energy, so your body doesn’t need to release as much insulin.
The intensity of your exercise can also affect your blood sugar levels. If you exercise at a higher intensity, your body will need to release more insulin to balance your blood sugar levels. Generally, someone taking a moderate walk won’t notice a significant effect on blood sugar levels, while someone going for a 5-mile run will.
Finally, how long you exercise can also affect your blood sugar levels. If you exercise for a longer period of time, your body will need to release more insulin to keep your blood sugar levels in balance.
Exercise Lowers HbA1C Levels
HbA1C (glycated hemoglobin) measures your average blood sugar levels over the past three months. If you have diabetes, your doctor likely runs this blood test every three months.
Research has shown that regular exercise can help to lower HbA1C levels. For example, one study showed that people with type 2 diabetes who exercised for 90 minutes, three days per week for three months, lowered their HbA1C levels by almost 2%, regardless of any weight loss.
Another study showed that people with type 2 diabetes who did a combination of aerobic and resistance exercise lowered their HbA1C levels by 0.6% more than those who just did aerobic exercise or just did resistance exercise.
So, regular exercise is an excellent place to start if you want to lower your HbA1C levels.
Safe Blood Sugar Ranges for Exercise
Maintaining safe blood sugar levels before, during, and after exercise is important.
If you have diabetes, your blood sugar level should be at least 100 mg/dL before you begin any type of exercise. According to Mayo Clinic, If your blood sugar is below 100 mg/dL, you should consume a small snack of about 15grams of carbohydrates to raise your blood sugar.
Fast-acting carbs, such as fruit juice, fruit, or even glucose tablets, will have the quickest effect on blood sugar levels.
If your blood sugar level exceeds 250 mg/dL, you should not exercise. Above 250 mg/dL is considered unsafe for exercise, and you’re at an increased risk of ketoacidosis if your blood sugar gets too high. If your blood sugar is above 250 mg/dL, we recommend holding off on exercise until your blood sugar levels are lower. In the meantime, focus on your diet and getting enough sleep; your blood sugar levels should naturally lower significantly. Once you are below 250 mg/dL, you’re in a safe range for exercise.
You should also monitor your blood sugar levels more during and after exercise.
Monitoring Blood Sugar Levels During Exercise
If you have diabetes, monitoring your blood sugar levels before, during, and after exercise is essential. This will help you to keep your blood sugar levels in a safe range and avoid any complications.
There are a few different ways to monitor your blood sugar levels during exercise.
One way is to use a continuous glucose monitor (CGM). A CGM is a small sensor that is placed under your skin and measures your blood sugar levels in real-time. This can be helpful if you have diabetes because it can help you see how your blood sugar levels change during exercise.
Another way to monitor your blood sugar levels during exercise is to use a glucometer. A glucometer is a small, handheld device that you can use to test your blood sugar levels. You will need to prick your finger with a small needle to get a drop of blood, which you will place on a test strip. The glucometer will then give you a reading of your blood sugar level.
If you are using a glucometer, it is important to test your blood sugar levels before and after exercise. You should also test your blood sugar levels during exercise if you feel any symptoms of low or high blood sugar, such as sweating, feeling shaky, or feeling dizzy.
When To Stop Exercise - Low Blood Sugar
You should stop exercising immediately if:
- Your blood sugar levels fall below 70 mg/dL
- You feel dizzy or lightheaded
- You have blurred vision
- You feel shaky or anxious
These are all signs of low blood sugar levels and can be very dangerous. If you experience any of these symptoms, stop exercising and check your blood sugar levels.
If your blood sugar levels are below 70 mg/dL, the American Diabetes Association recommends following the 15-15 rule. You should consume 15 grams of fast-acting carbohydrates such as fruit juice or glucose tablets. Then, wait 15 minutes and recheck your blood sugar. If your blood sugar levels are below 100 mg/dL, consume another 15 grams of fast-acting carbs and recheck your levels in 15 minutes.
Once your blood sugar levels are above 100 mg/dL, it is safe to continue exercising.
Keep in mind that with most moderate exercise, episodes of low blood sugar (hypoglycemia) are not common. Low blood sugar is most likely to occur if:
- You haven’t eaten in a while or are fasting
- You’ve taken insulin or another medication that can lower blood sugar
- You’ve exercised strenuously
- You’ve exercised for an extended period of time
When To Stop Exercise - High Blood Sugar
You should stop exercising immediately if:
- Your blood sugar levels rise above 250 mg/dL
- You feel nauseous or vomit
- You have difficulty breathing
- You have ketones in your urine
These are all signs of high blood sugar levels and can be very dangerous. If you experience any of these symptoms, stop exercising and check your blood sugar levels. If you find ketones in your urine and your blood sugar is over 250 mg/dL, you should immediately contact your doctor. Your doctor will advise you on how to best and safely lower your blood sugar levels. Please visit your nearest urgent care or emergency room if you cannot reach your doctor. High blood sugar levels with ketones can be life-threatening and shouldn’t be ignored.
You should not exercise if your blood sugar levels are above 250 mg/dL.
The Best Time of Day To Exercise
Research has suggested if you have diabetes, the best time of day to exercise is in the early afternoon. This study found that men with type 2 diabetes had better overall blood sugar levels with afternoon exercises versus early morning exercise.
Another study found that beginning exercise 30 minutes after eating a meal can help blood sugar levels from rising or lowering as much during exercise.
Exercise and maintaining an active lifestyle are important for diabetes management and overall health and well-being. While some times of the day may be advantageous for exercise, the most important thing is to find a convenient time for you and your schedule. You are making lifestyle changes that you want to become a permanent part of your life. So be sure to pick a time that will allow you to incorporate exercise into your schedule and won’t be inconvenient to your other obligations.
Risks of Exercising With Diabetes
There are some risks associated with exercising if you have diabetes. These risks include low blood sugar levels (hypoglycemia), high blood sugar levels (hyperglycemia), and ketoacidosis.
Hypoglycemia is a condition where your blood sugar levels drop too low. This can happen if you exercise for a long time or if you do not eat enough before or after exercise. Symptoms of hypoglycemia include feeling shaky, feeling dizzy, sweating, and having a fast heart rate.
Hyperglycemia is a condition where your blood sugar levels rise too high. This can happen if you do not monitor your blood sugar levels during exercise or if you eat too much before or after exercise, particularly if you eat a lot of carbohydrates. Symptoms of hyperglycemia include feeling thirsty, having a dry mouth, feeling tired, and needing to urinate more often.
Ketoacidosis is a serious complication that can occur if you have diabetes. It happens when your body does not have enough insulin and begins to break down fat for energy. This process produces ketones, which can build up in the blood and cause serious health problems. Symptoms of ketoacidosis include nausea, vomiting, abdominal pain, confusion, and difficulty breathing. If you experience these symptoms, stop exercising and call your doctor immediately.
Exercising with diabetes comes with risks, but those risks can be managed with proper planning and preparation. Be sure to talk to your doctor before you start any exercise program. They can help you create a safe exercise plan to help manage your diabetes.
Cautions for Exercising if You Take Insulin
If you take insulin, there are some special considerations you need to be aware of before starting an exercise program. When you exercise, your body burns more sugar for energy. This can cause your blood sugar levels to drop too low, which can be dangerous. To help prevent this from happening, you may need to adjust your insulin dose or eat a snack before exercising.
If you take insulin, discussing your exercise plans with your doctor before starting is especially important. Your doctor may need to adjust and lower your medication use.
You should also check your blood sugar levels before, during, and after exercise. If you take insulin, you are at higher risk of both low blood sugar and high blood sugar. Make sure you’re prepared for both scenarios when you exercise. We recommend keeping a small bag with you that includes your diabetes testing supplies and fast-acting carbs should you need them.
Exercise is a vital part of managing diabetes, so it is important to exercise even if you take insulin.
The Bottom Line
With a little planning and preparation, you can safely exercise with diabetes. Just be sure to talk to your doctor before starting any new exercise program so they can help create a plan that is safe for you. Exercising comes with its own set of risks, but by managing your blood sugar levels carefully, you can minimize those risks and stay healthy and active.
For people with diabetes, safe blood sugar ranges for exercise are above 100 mg/dL and below 250 mg/dL. If you are above or below this range, do not exercise until your blood sugar is more stable and within this range.
If your blood sugar falls outside of this range during exercise, or if you feel unwell at any time, it is important to stop immediately. Check your blood sugar levels and take the appropriate corrective action.
