Exercise and Type 1 Diabetes

Exercise

There is no doubt that exercise is good for everyone. You may read that exercise helps to control blood glucose levels – this is very true, but mainly for people with Type 2 diabetes. For those people with Type 1 diabetes, exercise can cause some problems if it is not dealt with properly.

Learn how to incorporate exercise into your daily diabetes management, then you can reap the benefits of an active life without compromising your blood glucose control.

Important note: Always check with your doctor or diabetes team before starting any exercise programme. There may be reason for you to take special precautions or avoid some forms of exercise.

More general information on exercising safely and tips for increasing your level of activity can be found in “Physical Activity“.

Here, we look at the ways in which exercise or sports can be fitted into your diabetes management, with the right adjustments in diet and/or insulin.

The relationship between exercise, blood glucose and insulin

Firstly, we need to consider what normally happens in people who do not have diabetes. This will help you to understand why adjustments need to be made to your treatment plan when you exercise.

Exercising muscles need fuel for energy and this is supplied by glucose and fatty acids. It is the level of insulin in the blood that controls the availability of both of these fuels.

Glucose is normally stored in the form of glycogen in muscles and in the liver. When exercising, the glucose stored locally in the muscles is used up first. Then the muscles take glucose from the bloodstream. This lowers the blood glucose level. The falling blood glucose level acts as a signal to the beta cells to reduce their insulin production. This lowers the level of insulin in the blood. Glucose is then released from the liver to top up the blood glucose level in order to keep it within the normal range.

The critical point in this series of events is the decline in insulin production, which occurs in response to the exercise and drop in blood glucose. Low insulin levels encourage the liver to release glucose into the bloodstream. Low insulin levels also favour the breakdown of fats into fatty acids, providing the other source of fuel for exercising muscles.

Note: insulin secretion is reduced, but not stopped altogether. Sufficient insulin is produced so that cells can access the glucose in the bloodstream.

So, exercise lowers the blood glucose level. This brings about a reduction in insulin secretion. Lower insulin levels favour the release of glucose and fatty acids. The blood glucose level is maintained and the exercising muscles are provided with plenty of fuel for energy.

Exercise, blood glucose and insulin in people with Type 1 diabetes

People controlling diabetes with insulin injections do not have any immediate or fine control over their insulin levels (unless using an insulin pump). Let us look at what happens when you, someone with Type 1 diabetes, start exercising. To begin with, we will assume that you have taken normal doses of insulin, as usual, and that your blood glucose is running at near-normal levels.

Glucose, stored as glycogen in the muscles, will be used be up first. Then the muscles will start taking glucose from the bloodstream. Because insulin levels are normal (or even high) the liver does not release more glucose into the bloodstream. The relatively high insulin level in the blood also means that the muscles will use glucose as a fuel, in preference to fatty acids. The result is a falling blood glucose level, which will keep on falling unless it is topped up.

So, exercise causes the blood glucose to drop and this will cause potentially dangerous hypoglycaemia (low blood glucose) unless extra glucose is supplied from the diet. This means that you would normally need to eat extra carbohydrates when you exercise.

Now, let’s suppose that your blood glucose level is running high and you want to exercise. You may think (not unreasonably) that exercise will bring your blood glucose level down. Indeed, it may do; but it could also raise your blood glucose level even further.

Often, blood glucose is high because there is not enough insulin in the blood. If this is the case and insulin levels are really low then consider what may happen when you exercise.

Low insulin levels cause the liver to release glucose into the bloodstream and the blood glucose level rises. This happens even if blood glucose levels are already high.

Also, muscles will be using more fatty acids as a fuel instead of glucose. If fatty acids are burned in excess then by-products called ketones may build up. This causes the blood to become acidic and may lead to a potentially fatal condition called diabetic ketoacidosis, or DKA.

So, exercising when blood glucose levels are high (if insulin levels are low) can be dangerous.

Putting the theory into practise

To recap then, exercise usually causes the blood glucose level to drop. However, if you do not have enough insulin in your body, exercise can cause the blood glucose level to rise and you may be at risk of developing diabetic ketoacidosis.

Remember, your aim is to keep blood glucose levels close to normal wherever possible. Good control is not only important for your long-term health; it is also necessary for your safety and will aid athletic performance when exercising.

There are two ways to adjust for the effects of exercise:

• by eating extra carbohydrates and/or
• by taking less insulin

You will need to learn how to adapt your usual diabetes regimen in order to keep blood glucose levels well controlled when exercising. Your doctor and diabetes nurse will be able to help you with this.

Eating extra carbohydrates

How much extra carbohydrate is needed is a very individual thing. It will also depend on the length of time that you exercise for and how strenuous the activity is. You may need extra starchy foods at the previous meal and/or snacks or sugary foods before, during, and after exercising.

Use your blood glucose monitoring results to gage how much food you need to eat (and when) for that particular activity.

Make sure that you always have plenty of food available, including glucose tablets or a glucose drink, in case of hypoglycaemia during the activity.

Muscle cells will continue to take more glucose from the bloodstream for several hours after strenuous exercise. This means that you may be at risk of hypoglycaemia for up to 18 hours after exercising. Test your blood glucose level at regular intervals during this period and eat extra carbohydrate as required. Be sure to have a good bedtime snack after exercising in the evening.

Taking less insulin

You can adjust for exercise by reducing your insulin dose(s), however this should be done with caution. Consult your doctor or a member of the diabetes team; they will be able to provide you with specific guidelines for adjusting your insulin doses.

Do note that, having altered your dose of insulin, you are effectively committed to exercising. Remember that if your exercise class, training session or sports match is then cancelled you are at risk of high blood glucose levels. If this does happen you may need to find an alternative activity, or eat less in order to prevent your blood glucose levels from rising too high.

Trial and error

There are no magic formulas that you can rely on for perfect blood glucose control in diabetes. At the end of the day it comes down to learning what works and what doesn’t work – for you. Use frequent blood glucose monitoring. Make a note of your test results and the adjustments you have made to your diet and/or insulin and learn by trial and error.

Guidelines for exercising

Here are some simple guidelines which should hep you to maintain good control whilst exercising in a safe and enjoyable manner.

Blood glucose levels beforehand:

• Do not exercise if your fasting (early morning) blood glucose level is more than 14 mmol/l
• Do not exercise if you test positive for ketones in your urine
• If your blood glucose level is less than 6 mmol/l you may need some extra carbohydrate before you start exercising

Blood glucose monitoring:

• Test your blood glucose levels before, during and after exercise
• Keep detailed records to help you identify when changes to your diet and/or insulin are needed
• Learn how your blood glucose levels react to different types of exercise

Adjusting the treatment plan

• Avoid hypoglycaemia by eating extra carbohydrates before, during and after exercising as necessary
• Learn how to adjust your insulin dose(s) with guidance from your diabetes team

Exercise warnings

• Check with your doctor before embarking on a new exercise regimen
• Always include a proper warm-up and cool-down period (5 – 10 mins each)
• Stick to low-impact exercise if you have neuropathy – cycling, swimming and rowing are all preferable to running or dancing
• Wear comfortable footwear that fits well
• Check your feet after exercising for any signs of sores or blisters
• Make sure that glucose and carbohydrate foods are available at all times and wear or carry diabetic ID
• Educate those around you about diabetes – the signs and symptoms of hypoglycaemia may be confused with those of over-exertion by someone who doesn’t know any better
• Avoid exercising limbs in which you have recently injected insulin – this can cause the insulin to be absorbed very quickly, resulting in sudden or severe hypoglycaemia