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68
VOLUME 9 NUMBER 2 • JUNE 2012
REPORT
SA JOURNAL OF DIABETES & VASCULAR DISEASE
The risk of hypoglycaemia can be managed by increasing
carbohydrate (CHO) intake before, during and after exercise. The
amount of carbohydrate consumed is dependent on the type and
dosage of insulin injected, specifically the time of peak action,
body mass of the exercising person and energy expenditure of
the exercise. Riddel recommends 1.0 g CHO/kg/hour. This can be
ingested in the form of a 6–8% glucose drink, such as Energade
(6.6 g/100 ml) and Powerade (5.6 g/100 ml).
12
Insulin dosage reduction
In order to reduce hypoglycaemia, Rabasa-Lohret suggested that
one could reduce the insulin dosage in accordance with the intensity
of the exercise.
19
He suggested reducing the pre-meal dosage by
25% when exercising at a low intensity, a 50% reduction when
exercising at a moderate intensity and up to 75% reduction when
exercising at a high intensity. Some people find, however, that
lowering their pre-meal insulin dose may cause an initial rise in their
blood glucose, which impairs their performance.
19
Grimm found it was more important to supplement with
carbohydrates than to lower the insulin dosage to prevent
hypoglycaemia. His study indicated that the intensity and duration
of exercise would determine the patient’s carbohydrate intake and
insulin adjustments. He suggested 15–100 g of carbohydrate per
hour during exercise, if the exercise is performed at the time of
the peak effect of insulin action. Furthermore, daily insulin dosages
should be decreased by 20–30% if exercising for one hour or more
(Table 1).
20
Sprinting to prevent hypoglycaemia during and after exercise
Guelfi revealed a novel approach to preventing hypoglycaemia
during moderate-intensity exercise.
21
She suggested going for
four-second maximal sprints every two minutes in the middle of
a moderate-intensity workout to simulate the activity patterns of
intermittent sport. This high-intensity activity increases adrenal
hormone levels, which leads to less hypoglycaemia both during and
for several hours after exercise.
21
Post-exercise snacks and insulin adjustments to prevent post-
exercise hypoglycaemia
The key to good glycaemic control is strategic carbohydrate
replenishment and insulin lowering post exercise. If one has
exercised at a moderate to high intensity for more than 45 minutes,
it is imperative to take the necessary snacks before going to bed
and/or to decrease one’s insulin dosage strategically at each meal
and at bedtime over the next 24 hours.
Glycogen-replenishment drinks and low-dose insulin post
exercise may speed up liver and muscle glycogen replenishment
in athletes with diabetes who exercise for more than two hours
daily. Endurance athletes may require a combination of 0.8 g/kg
carbohydrate and 0.4 g/kg protein in their replenishment drinks.
This combination is known to hasten glycogen replenishment,
creating an essential substrate that can convert to glucose when
the blood glucose levels drop too low.
22
Previous hypoglycaemic episodes and moderate-intensity
exercise may lead to more hypoglycaemia
Studies have shown a blunted counter-regulatory response
to hypoglycaemia following low/moderate-intensity exercise.
Furthermore, hypoglycaemia prior to exercise, even in the
sedentary state, attenuates the counter-regulatory response to
exercise. In other words, hypoglycaemia begets hypoglycaemia.
23
Some researchers suggest increasing one’s blood glucose levels and
avoiding hypoglycaemia for two weeks prior to an endurance event
in order to prevent hypoglycaemia during the event.
Exercise, sleep and unchanged insulin may lead to nocturnal
hypoglycaemia
If a person with diabetes exercises for more than 45 minutes, he/
she will utilise the majority of the muscle and liver glycogen stores
and is thus more likely to develop hypoglycaemia over the next
24 hours. Sleep may decrease one’s autonomic nervous system
responses to hypoglycaemia. If a patient does not reduce his/her
insulin dosage and take an appropriate bedtime snack, he/she has
a good chance of developing nocturnal hypoglycaemia.
Is insulin pump therapy the answer to hypoglycaemia?
Insulin pump therapy may provide a solution to hypoglycaemia for
a number of reasons:
In most cases, patients infuse 20% less insulin when using a
•
pump versus multiple daily injections.
The depot of insulin remains in the pump and only small
•
amounts of insulin are infused under the skin and circulate.
Pump users can adjust their insulin dosages in fractions, which
•
makes insulin adjustments far more accurate.
An insulin pump can be disconnected during exercise and basal
•
rates can be reduced for an appropriate period before exercise
to lower circulating insulin levels during exercise.
Pump users can decrease their basal rates of insulin replacement
•
at critical times during the night and early morning to reduce
the incidence of nocturnal hypoglycaemia.
Hyperglycaemia
Hyperglycaemia may be common in exercises such as squash or
high-intensity spinning or resistance training, due to an excessive
counter-regulatory hormonal response. In the non-diabetic,
circulating counter-regulatory hormones decrease rapidly post
exercise and insulin levels increase, allowing for rapid glycogen
replenishment and therefore a rapid decrease in glucose levels.
Most patients with type 1 diabetes choose to exercise during the
tail effect of their insulin action, or they will decrease their insulin
dosage to avoid hypoglycaemia. Therefore, post-exercise insulin
levels may be low. With high post-exercise circulating counter-
regulatory hormones and low insulin levels in the patient with
type 1 diabetes, the patient’s blood glucose levels may remain high
Intensity/
duration
Length of exercise
< 20 min 20–60 min > 60 min
< 60% of maxi-
mal heart rate
0 g
15 g
30 g/h
60–75% of maxi-
mal heart rate
15 g
30 g
75 g/h
↓
insulin dosage 20%
> 75% of maxi-
mal heart rate
30 g
75 g
↓
insulin dosage
0–20%
100 g/h
↓
insulin dosage 30%
Adapted from Grimm
et al
.,
Diabetes Metab
2004:
30
: 465–470.
Table 1.
Extra carbohydrate and insulin adjustments (depending on duration
and intensity) to prevent hypoglycaemia in patients with type 1 diabetes
engaging in physical activity.