To get straight to the point: yes, exercise can lower blood sugar. But, exercise can also raise blood sugar. It depends on what kind of exercise you’re doing. Aerobic exercise will likely lower blood sugar, while anaerobic exercise will likely raise blood sugar.
Aerobic exercise is what you might call cardio. Essentially, it is activity that will get your heart-rate going for a longer period of time. Examples of this are cycling, jogging, swimming, and rowing.
This increases blood flow in the body, which in turn promotes insulin sensitivity. Additionally, the muscles use up glucose. In other words, cardio lowers blood sugar because the body is able to transport more glucose to the cells than it normally would.
Anaerobic exercise is a shorter and more intense kind of activity; it will get you out of breath quickly. Examples of this are interval training, weightlifting, sprinting, and jumping.
More specifically, anaerobic exercise doesn’t rely on oxygen. Instead, it relies on energy from the muscles. To get that energy, the body increases hormones – like adrenaline – which promote the liver to release its store of glucose. That extra release of glucose raises blood sugar levels.
So, does exercise lower blood sugar? Yes and no. But there are ways to keep blood sugar stable when you exercise. Read on to find out more!
When does Exercise Lower Blood Sugar?
If you’re doing cardio, then exercise should always lower blood sugar. However, there are certain times of the day when you will be more insulin sensitive.
If exercise is adding to that insulin sensitivity, then you might end up with blood sugar that is too low. So, it’s best to think about how timing, insulin, and exercise will affect you.
Usually, insulin sensitivity decreases throughout the day (which can result in higher blood sugar). This is true for people with or without diabetes.
But, this can be different for those with insulin-dependent diabetes. You might find that your insulin medications actually result in less glucose being used in the morning. Effectively, this would make you less insulin sensitive in the morning.
Christel Oerum – the popular fitness blogger with type 1 diabetes – explains: “our basal insulin will vary throughout the day […] I’ll need more insulin to cover a given amount of carbs in the morning than I do for the exact same type and amount of carbs at night”.
In that case, it might be easier for you to exercise at a different time of day. Clearly, it’s a fairly individual matter. So, it all comes down to trial-and-error.
When doing anaerobic exercise, the situation could be in reverse. Since anaerobic exercise raises blood sugar, you might consider doing it when you are more insulin-sensitive, in order to balance out the blood sugar levels.
That’s also not to say that you can’t exercise at certain times of the day: you just need to know how your body will respond in order to plan ahead.
How to Manage Blood Sugar when Exercising
As always, testing blood sugar levels is a good idea. You should test before, during (if possible), and after exercise. If you can use a continuous glucose monitor (CGM), that would make testing during exercise even easier.
These numbers will help you establish what your blood sugar levels should be during exercise. It’s especially useful to consult with a doctor if it’s new to you.
But, once you’ve figured out how your body responds, it should be fairly straightforward to establish how to manage blood sugar when exercising.
For instance, you might want to eat a snack prior to your aerobic exercise – or, particularly if you want to lose weight and want to reduce carb intake – reduce insulin for your meal. And, if doing anaerobic exercise, you might want to increase insulin.
So, don’t feel discouraged by how blood sugar will change. Just be prepared. Always make sure to have a high-carb snack with you; eat it while exercising if you need to!
Exercising with diabetes is manageable: many athletes can attest to this. Jay Cutler, the professional American football player, and Scott Allan, the Scottish professional association football player both have type 1 diabetes.
Indeed, Christel Oerum is another inspiration – so much so that we’ve interviewed her!
Some other aspects to consider:
- Exercising together with others can be a good idea; you can help each other, especially if the other person is aware of your condition.
- Aim to finish exercise at least two hours before bed to avoid going low during sleep.
Unplanned exercise might happen, like running for the bus, helping a neighbour move furniture, or taking your kids to the playground. So, keep testing!
Usually, these occurrences will lower blood sugar: eat something. But you can’t know exactly what to do without knowing what your blood sugar is.
Don’t exercise intensely if your ketone levels are high. And, if you’re insulin-dependent, don’t exercise without any insulin in your body. Exercise can increase ketone levels. During exercise, ketones are used in burning fat and using energy.
But without insulin, the ketones will be made faster than they can be metabolised, which could lead to too many ketones (ketoacidosis).
This happens because your body starts to burn fat instead of carbohydrates, which then results in the release of ketones. The body uses ketones as a daily energy source, as well as glucose. During exercise you increase your fat burn, and this can lead to high levels of ketones.
Is it worth it?
By this point, you may be wondering whether thinking about all these aspects of exercise is worth it. Just like any area of diabetes management, exercising with diabetes will eventually come more naturally. Once you’ve figured out how your body behaves, it will be even easier.
Having these doubtful thoughts is not unusual: JDRF writes “studies show that many people with T1D do not engage in regular physical activity owing to a fear of hypoglycemia, or dangerously low blood-glucose levels”.
So, why do it? You’re probably aware that exercise is beneficial. And, this is especially true for those with diabetes, for various reasons.
First, those with diabetes are at higher risk of cardiovascular problems later in life. Regular exercise keeps the heart and blood vessels quite happy and healthy. Additionally, exercise prevents extra fat from building up around organs which would lead to insulin resistance.
For the short-term, exercise is a good way to burn off stress and release endorphins, keeping you happy. This is great since stress and diabetes are not the best companions.
Burning off that stress will also let you sleep better. Read more about diabetes and sleep here.
And those endorphins will help with a generally better mental health, including more self-confidence and better mood. That better mood goes hand in hand with the more everyday energy you get from regular exercise.
That doesn’t mean you need to become an athlete to manage your diabetes. Even staying active by gardening or going for walks will help you. And if you have certain strains on your body, try exercises like swimming which don’t rely on you to use the weight of your body.
It’s really an all-round plus!
Exercise: much more than Lower Blood Sugar
While exercise does indeed lower blood sugar – and raise it too – it is perfectly fine, and advisable, to exercise. Yes, it’s not always easy to manage, but to quote Christel Oerum:
“Finding your formula for exercise and diabetes can take time but it can be done […] I don’t think anyone should just accept “always” going high or low”.
Ultimately, exercise should be more than just low blood sugar. It’s a part of life that can make you healthier, happier, and will make diabetes management easier for both the long-term, and for other short-term areas.
Still not sure how exercise will affect your blood glucose and insulin dosage? Then let Hedia do the calculations when you enter activity into the diabetes assistant. Download it for free at the App Store or Google Play!