Monday July 28 2008
An extra 45 minutes a day could include a lunchtime walk
“People with diabetes can limit the impact of the condition simply by walking for an extra 45 minutes a day”, says The Guardian. A study found that exercise helped to keep blood sugar levels in check. The benefits of exercise in controlling blood sugar in people with diabetes are well-known and they are recommended, along with dietary change, to delay the onset of diabetes.
This study of 20 volunteers was too small to show any changes in blood sugar control, however it did confirm the feasibility of a simple programme in which each volunteer was given a pedometer and asked to walk an extra 45 minutes each day. This led to more than 10,000 steps a day in the group with diabetes, maintained for eight weeks. These results are encouraging. There was a measurable change in the ability of muscle cells to burn fat in people with diabetes, and in the ability of cells to use sugar in the diabetes and control groups. Further studies will be needed to show how these cellular changes are linked to the control of diabetes.
Where did the story come from?
Dr Michael Trenell and colleagues from the Diabetes Research Group at the Institute of Cellular Medicine and the Magnetic Resonance Centre at Newcastle University carried out the research. The study was funded by a grant from the Wellcome Trust and a fellowship from Diabetes UK. It was published online in the peer-reviewed medical journal Diabetes Care.
What kind of scientific study was this?
This was a cross-sectional study in which the researchers took 20 volunteers, 10 with and 10 without type 2 diabetes (controls). They were matched so that each person with diabetes was as similar as possible in age, sex, weight and habitual physical activity to a person in the control group. They performed a variety of tests on the participants before the study started, then asked them to increase the amount of daily physical activity for eight weeks, and measured this with a pedometer. They repeated the tests at two weeks and eight weeks.
The researchers were interested in whether there were differences between the groups in the activity of mitochondria in the muscle cells. Mitochondria are components of the cell that are thought to play a role in the development of type 2 diabetes by affecting the way the cells react to the hormone insulin. The researchers set out to measure differences in the activity of the mitochondria in the muscle at baseline and after physical activity in people with and without diabetes. They looked at how much of the enzyme “ATP” was used by the muscles, and how well lipids (fats) were metabolised. Measurements were done by magnetic resonance spectroscopy of muscles, a non-invasive technique that obtains information about the biochemical content of cells without the need for a biopsy.
The researchers used a pedometer at the start of the study to measure baseline physical activity. The pedometer is activated by movement, and is a validated method of recording physical activity. In this study, the pedometer was attached to the arm, and baseline activity levels were averaged over three days. Measures of diabetes control were also recorded for all volunteers, using blood tests, fasting plasma glucose, insulin sensitivity using HOMA and HbA1c.
Both groups were asked to increase their activity levels by setting a goal of an extra 45 minutes of walking a day. They wore the pedometers to check this, and also received phone calls from the research team.
What were the results of the study?
The 10 volunteers with diabetes were aged on average 59 years and had a BMI of 33 with a fasting blood sugar of 7.1mmol/L. The 10 control volunteers were aged on average 56 years, and had a BMI of 30 with lower fasting glucose, 5.5mmol/L, confirming the absence of diabetes. All the measurements taken at the start of the study were similar in the 10 people with diabetes when compared with those without diabetes. At baseline, they walked between 6,400 and 7,600 steps a day, used 12 micromols/ml/minute of ATP each, and had similar rates of lipid metabolism.
After increasing physical activity, the measures at eight weeks showed that the number of steps had increased to 12,322 per day on average for the people with diabetes, and to 9,187 steps per day for those without. There were no changes in basal ATP use as measured by the MRI spectroscopy, but lipid metabolism rates increased in the people with diabetes more than in the group of people without diabetes.
What interpretations did the researchers draw from these results?
The researchers say that in their study, “resting and maximal ATP turnover are not impaired in people with well-controlled type 2 diabetes compared to the matched controls”. They conclude that “increased unsupervised daily physical activity is sustainable and improves lipid oxidation independent of change in mitochondrial activity in people with type 2 diabetes”.
This supports the theory that pedometers encouraged an increase in walking, and that this improved their bodies' ability to store sugar and burn fat.
What does the NHS Knowledge Service make of this study?
This was a small study, which the researchers fully acknowledge was not powered, i.e. it was not large enough to detect changes in glucose control, which is clearly an important outcome that is of interest to people with diabetes. Other limitations mentioned by the researchers include:
- ATP production in the mitochondria of muscle cells may also be determined by other factors, such as oxygen demand, and it is not clear from this study what the normal variation in the measure of ATP production through the day or between people is. The significance of the changes in ATP turnover reported by this study would need this context for interpretation by non-experts in the field.
- As this was a cross-sectional study, it is possible that other differences between the groups, for example, differences in motivation to exercise, might have led to the difference in physical activity noted between those with diabetes and without diabetes. This is important and may have led to bias, or inaccuracies, in the study results since well-motivated people with diabetes may also have changed other aspects of their behaviour, such as diet, for the duration of the study.
Overall, this very small study in people with diabetes provides encouraging results, i.e. that physical activity such as walking can have benefits for the cellular metabolism of people with diabetes. From a more general point of view, an increase in steps of between 3,000 and 6,000 steps per day achieved with the simple pedometer device is also encouraging and supports current public health advice.
Sir Muir Gray adds...
Walking is the single best safest medicine you can take.