Tuesday September 18 2007
Aerobic exercise and weight training reduces blood sugar levels
Any kind of exercise can help people with type 2 diabetes, reported the news agency Reuters. It said that aerobic and resistance training lowered blood sugar levels in diabetic patients, and a combination of both lowered blood sugar levels even futher. Participants liked the exercise and, contrary to prevailing beliefs, stuck with the programme. It concluded that “doctors should prescribe exercise to every diabetes patient.”
This report was based on a trial with reliable results and shows, once again, the benefits of exercise. However, it is likely that people who are not given incentives, as they were in this trial, are less likely to exercise and therefore less likely to see the same benefits. Further research into the best way to motivate and sustain behaviour change in people with diabetes needs to be done.
Where did the story come from?
Doctor Ronald Sigal and colleagues from the University of Calgary and the University of Ottawa carried out this research. The Canadian Institutes of Health Research, Canadian Diabetes Association funded the study and it was published in the peer-reviewed medical journal, Annals of Internal Medicine.
What kind of scientific study was this?
This was a randomised controlled trial that assessed the effects of 6 months’ exercise on blood sugar levels in people with type 2 diabetes. The researchers recruited adults (aged 39–70) with type 2 diabetes and asked them to take part in 12 preliminary supervised exercise sessions over four weeks, in order to see whether they would be likely to stick with the exercise programme.
The 251 people who attended at least 10 of the 12 sessions were then randomly allocated to one of four groups: aerobic exercise (treadmills and exercise bikes), resistance exercise (seven different exercises on weight machines), combined aerobic and resistance exercise, or control (participants were asked to return their former level of activity). Exercise sessions were three times weekly for 22 weeks, starting with 15–20 minutes and increasing in length to 45 minutes, whilst also increasing in difficulty. Sessions were fully supervised by a personal trainer for the first month, and every other week subsequently.
The participants’ physicians were asked not to change their medication during the study unless absolutely necessary and the participants were all given advice on what they should eat in order to try and standardise diets between participants, but not to make them lose weight. The researchers measured and compared the change in the marker for blood sugar levels, haemoglobin A1C, between the start and the end of the study in all groups. A reduction in haemoglobin A1C level indicates an improvement in control of blood sugar (glycaemic control). The people assessing haemoglobin A1C levels were blinded to group allocation; however, it was not possible to keep the participants unaware of the group allocation.
What were the results of the study?
The researchers found that both aerobic and resistance exercise reduced levels of haemoglobin A1C compared with control over six months. Combining aerobic and resistance exercise reduced levels of haemoglobin A1C more than either type of exercise alone. Thirty people did not complete the study, 5% in the control group, 20% in the aerobic group, 11% in the resistance group, and 13% in the combined group. The majority of people who left the exercise groups did so because they did not have time or they lost interest.
What interpretations did the researchers draw from these results?
The researchers concluded that aerobic and resistance training can improve blood sugar control in type 2 diabetes, and combining these two types of exercise is even more effective.
What does the NHS Knowledge Service make of this study?
This was a good quality study, whose results are reliable, and indicate that different types of exercise can help people with type 2 diabetes to control their blood sugar levels. The main limitation to this study is that in real life it may be difficult to get people to participate in the levels of exercise needed to reap these benefits. In this study, researchers selected the most motivated people, provided free membership at an exercise facility and a personal trainer during the study, and all participants who completed 70% or more of the sessions were given six months further membership for free. This means that people who took part in this study were probably more motivated to exercise than the average person. In addition, type 2 diabetes often occurs in conjunction with other medical conditions, some of which may make vigorous exercise difficult, or potentially unfeasible.
Another point to note is that similar numbers of people in each group had to start taking or increase the dose of medication to control their blood sugar levels. Therefore, even with exercise, some people will still need medication to fully control their diabetes.
This study was not designed to follow people for long enough to determine whether the improvements in blood sugar level control resulted in reductions in adverse clinical outcomes associated with uncontrolled diabetes, such as heart attacks or kidney failure. Other studies have shown that changes of haemoglobin A1C of this magnitude are worthwhile and are associated with a reduction in the complications from diabetes.
Sir Muir Gray adds...
There is no better value, safer treatment then regular exercise; small changes in lifestyle – walking an extra 3,000 steps a day – can be of vital importance.