Exercise your control over type 1 diabetes

In his autobiography, five-time Olympic gold medallist Sir Steve Redgrave credits the treatment he received from consultant diabetologist, Dr Ian Gallen, for enabling him to win his fifth Olympic gold medal for rowing in Sydney in 2000. 

Before this Olympic win, Sir Steve had been told by two consultants that he would have to retire because of his type 1 diabetes. However, Dr Gallen – who has a background in physiology and was familiar with rowing – decided to see what he could do. And the rest is history. 

Sir Steve spread the word about Dr Gallen to other sports people and the demand for his services grew. Eventually, the NHS allowed him to set up a separate diabetes sports clinic, which now receives referrals from all over the UK.

At the clinic, patients spend 30 minutes with a dietitian and 30 minutes with a diabetes nurse specialist. Both specialists review the patient’s diabetes management and subsequently create management strategies to help them to handle their condition better.

Dr Gallen spoke at a recent ‘Optimising insulin pump therapy’ meeting in Dublin –  a collaborative venture between Bayer Diabetes Care and Medtronic Limited. He told the meeting that there are key differences between managing endurance sports (eg. cycling) and managing sports that produce short intense exercise (eg. sprinting).

Dietetics is also very important for serious sports people with type 1 diabetes as they need a lot of calories and their insulin regime must reflect this.

According to Dr Gallen, the first things you need to know about your patient are:

• What sport they play

• What time of the day they play

• How intensely they play

• For how long they play.

Exercise and diabetes

The key points regarding diabetes and exercise include:

• Glucose dispersal into muscle is increased after exercise

• The ability to produce a counter-regulatory hormone response is impaired by exercise

• The ability to produce a counter-regulatory hormone response is impaired by hypoglycaemia. 

“Someone with diabetes, who is doing exercise like long-distance cycling, is burning glucose instead of fat,” said Dr Gallen. 

“The way we address this is by trying to get the circulating insulin levels down as low as possible during exercise; to try and make the physiology of the person as normal as possible.”

Dr Gallen said this can be done by:

• Reducing background insulin levels

• Taking extra glucose – but you need to work out how much

• Stimulating the counter-regulatory hormone response – which is possible.

Know your exercise

Moderate-intensity, long-duration sports in the late post-prandial period are associated with severe falls in blood glucose. Meanwhile, short high-intensity exercise occurring in the late post-prandial period is associated with high blood sugars. If your patient is involved in a team sport, you need to find out what sort of game they play and what position they play in.

For example, someone who plays in the forward position of a rugby team will spend the whole match running back and forth. They are always working, but at a relatively slow rate, so their body will react similarly to a runner and their sugar levels will fall. However, someone who plays on the wing of the same team will only do short bursts of running once or twice every 10 minutes, so their sugar levels will rise.

Dr Gallen suggests that patients whose blood sugars are at risk of rising to high levels during exercise – and who use an insulin pump – should experiment by taking a half-unit as a bolus, 30 minutes before their match and work up from there. If the patient does not use a pump, they could inject half a unit, 30 minutes before the match. 

Nocturnal hypoglycaemia

Studies show that there is a rise in blood glucose while doing exercise and there is a very marked increase in glucose uptake 10-12 hours after exercise. This means that for the same insulin dose there is a 25% increase in glucose uptake into muscle. A person can have very low levels of insulin during exercise and their blood sugar will still come down, provided their muscles are contracting.

If someone is doing exercise every single day, they do not need to reduce their night-time dose of insulin. However, if someone is exercising less than three days a week, they will need to alter their regime to avoid hypoglycaemia on the nights following exercise. 

They can do this by cutting their long-term insulin dose down by either reducing their bolus by 25% or reducing the basal component on their multiple daily injections by 20-25% on the days that they exercise.

High-intensity exercise

If the patient is exercising at a high intensity, the tendency for nocturnal hypoglycaemia is even more marked. This includes track and field sports where there are periods of high-intensity exercise and low-intensity exercise. Those patients will have more hypoglycaemia and will have lower blood glucose measured by continuous glucose monitoring (CGM).

During exercise, the patient’s blood sugar might be higher, so they may have less hypoglycaemia, but they will be more sensitive to hypoglycaemia at night-time following the exercise.  “For some reason, women are less likely to have hypoglycaemic unawareness after exercise than men are. We don’t know why that is,” explained Dr Gallen.

Hypoglycaemia during exercise

Research carried out by Steve Davis in the US shows that a period of hypoglycaemia the day before exercise abolishes the counter-regulatory hormonal response to exercise. This leaves the person at severe risk of hypoglycaemia during exercise.

In addition, exercise abolishes the counter-regulatory response to hypoglycaemia, leaving the person at risk of hypoglycaemia at night. The more severe the hypoglycaemia, the more marked the effect is. But again, women are protected from this effect. 

According to Dr Gallen, you must determine whether or not your patient should exercise within 24 hours of having hypoglycaemia. Unless they are being supervised, it is unlikely that they should.

“If the exercise is intermittent and the person is sleeping on their own, particularly if it is a man, try to work out if they can set an alarm to wake them in the middle of the night. Or perhaps there are people in the shared house or hall or residence who might have a look in at them or be aware of what to do if there were signs of hypoglycaemia,” Dr Gallen said.

Meanwhile, it is vitally important when talking to young men and women that you counsel them specifically about the interaction between sport, alcohol and hypoglycaemia. 

Glycaemic control 

Having identified the type of exercise your patient wants to do, you can work out whether their blood sugar is likely to rise or fall. There are different strategies depending on whether the exercise is done in the immediate post-meal post-insulin period, or in the late post-insulin shot period. 

You can reduce pre-exercise bolus insulin but it does require pre-planning. When exercise is occurring within 90 minutes of the patient’s bolus pump shot or bolus injection, it is possible to adjust the meal-related dose. “You could do this by suggesting a 25% reduction, get them to check their blood sugar after and see was that enough. Then you could give them some guidelines about how to reduce it further,” said Dr Gallen.

This method reduces hypoglycaemia during and after exercise, and it also reduces the carbohydrate requirement of the patient. However, this method also requires pre-planning, it is not helpful for spontaneous exercise and it is not helpful for late post-prandial exercise.

The patient can reduce basal insulin, but they need to replace it with a quick shot of insulin after they finish exercising or they will suffer hyperglycaemia.

Extra carbohydrate

“If the patient is not on an insulin pump, all you can do is to give them extra carbohydrate,” said Dr Gallen. “There is no point giving more than 60g of carbon hydrogen oxygen (CHO), because there is evidence that the body can only absorb 60g of CHO per hour. So giving more than this would just add to post-exercise hypoglycaemia.”

However, the patient must take the extra carbohydrate while exercising, which might not be practical. Also, this process is counter-productive if patients are exercising to control body weight, as 60g of carbohydrate provides 240 calories. “It is better to take glucose in small bursts during exercise than all at the start,” said Dr Gallen. 

He advises patients who play team sports to keep a watery drink by the touchline, drink it as needed and take six dextrosol tablets or four jelly babies every 20 minutes. Sports drinks also work very well for cyclists, but are less convenient for swimmers.

So, while taking extra carbohydrate is useful for unplanned or prolonged exercise, it may not be possible with some forms of exercise. Furthermore, it is not helpful when weight control is important and it is easy to over-replace glucose, leading to hyperglycaemia.

Pump therapy

Dr Gallen advised that, for endurance sports, the patient’s dose should be reduced to 20% of the normal infusion rate, 30 minutes before exercise. Then, it should be restarted at a normal basal rate shortly before finishing, or immediately after the exercise if the former is not practicable.

“For all exercise, you need to reduce the nocturnal insulin infusion rate if the exercise is less frequent than every three days. If someone is doing exercise every single day, you don’t need to do that because their basal dose will have come down and stayed down,” said Dr Gallen.

Correct basal dose

In theory, pump therapy should enable basal insulin to be markedly reduced or suspended during exercise. It enables rapid post-exercise adjustment, and it allows post-exercise bolus dose and post-exercise nocturnal basal dose to be reduced and pre-programmed.

“To my mind, this is the gold standard,” said Dr Gallen. 

“However, you need to know when to restart pump therapy and with how much.”

For endurance sports, Dr Gallen recommends suspending pump therapy during the exercise period. For sprint-type sports, he recommends giving 50-75% of the normal basal dose. The basal dose should be adjusted 30-60 minutes before exercise – that is suspended or reduced by 50-75%.

While healthcare workers worry about ketosis when insulin is stopped or reduced, ketosis is only a problem in resting hyperglycaemic patients. This is because it accumulates. In exercising patients, every molecule is burnt so it doesn’t accumulate. But as soon as they stop exercising the ketones can build up. 

This means that for a sport that lasts for any length of time, such as cycling, the patient should start taking insulin from the pump about 30 minutes before they finish exercising. But this is not practical for people like rugby players, who should give themselves a shot of insulin as soon as they stop exercising. They should also rub their skin for quicker insulin absorption.

Insulin pump therapy offers flexibility and rapid changes in post-exercise insulin infusion rates. However, this therapy is expensive and may not be practical for contact sports like judo, rugby or basketball. The advantages of reducing basal insulin after exercise is that it reduces nocturnal hypoglycaemia. However, it may cause morning hyperglycaemia.