by Marlene Busko
The beneficial effect of exercise on glucose control in patients with type 2 diabetes is related to improved cardiorespiratory fitness and a shrinking waistline, a new study suggests. Other effects of exercise — such as improved VO2 max, muscle mass, or fat distribution — were not linked with better HbA1c levels.
The results have clinical implications for the design of exercise training programs used to treat individuals with type 2 diabetes and provide further evidence that combining aerobic exercise with resistance training is the best approach, something guidelines already stress, says senior author Timothy S. Church, MD, from the Pennington Biomedical Research Center, Baton Rouge, Louisiana.
The new findings come from a secondary analysis of the Health Benefits of Aerobic and Resistance Training in Individuals with Type 2 Diabetes (HART-D) trial in individuals with complete follow-up data; the original results, published in the Journal of the American Medical Society in 2010 (JAMA. 2010;304:2253-2262), showed that 9 months of supervised aerobic training, resistance training, or both had a similar, favorable impact on HbA1c levels.
The research is published online May 13 in Diabetes Care.
Trim the Tummy, Gain Better Glucose Control
According to the authors, previous studies probing how body fat distribution, muscle strength, and fitness influenced long-term glucose control either had small, homogeneous samples or lacked a control group.
The HART-D trial "created a unique opportunity to really look at what [aspect of exercise] was creating a positive change in HbA1c," Dr. Church told Medscape Medical News.
The trial randomized 262 sedentary patients to a control group or to 3 types of exercise for 9 months. They all had type 2 diabetes that was not optimally controlled: 20% had heart disease, and 20% had neuropathy. "These were high-risk individuals with diabetes…what you see in the clinic," Dr. Church said.
The current analysis examined data from 201 of these participants with complete follow-up data. These patients were diverse: 39% were African American and 64% were women, and they ranged in age from 30 to 75 years. Overall, they were obese (mean body mass index [BMI], about 35) and middle-aged (mean age, 58 years) with relatively poor baseline fitness.
The aerobic exercise consisted of brisk walking on an inclined treadmill, at 50% to 80% of maximal cardiorespiratory fitness. The resistance training consisted of standard weight-bearing exercises in the gym.
On average, patients in the weight-lifting group or the aerobic group spent 140 minutes per week in the gym, and patients in the combined exercise group spent 110 minutes a week doing aerobic exercise and 30 minutes a week doing resistance training, Dr. Church said.
The researchers looked for changes from baseline to 9 months in HbA1c levels, weight, BMI, waist circumference, body fat, measures of fat mass, VO2, and leg muscle strength and estimated effort expended during exercise, or estimated metabolic equivalents of task (METs). Dual-energy X-ray absorptiometry (DEXA) was used to determine the participants' body fat composition.
Participants with increased estimated METs and reduced waist circumference were 2.81 times more likely to have lower HbA1c levels and a reduction in the use of medication for type 2 diabetes compared with those without improved fitness and central adiposity.
In the current study, "we didn't see things like changes in muscle mass or change in fat mass," said Dr. Church. "It was surprising to see fitness — measured by how long you stay on a treadmill — and belly fat as the big drivers" behind better glucose control.
Combined Aerobic and Resistance Training Is Best
Much like a drug-dosing study, this trial was designed to determine the optimal exercise regimen, not to find out how to get people to exercise, Dr. Church explained.
The original HART-D study involved more than 20,000 supervised exercise sessions, he noted, and participants had excellent compliance (more than 80% adhered to the program).
In a real-world setting, patients can perform aerobic exercise without supervision, although initial direction is needed for resistance training, he conceded. Patients can be counseled about attending local YMCAs or doing home-based exercise programs.
"The [new] study provides more evidence that the optimal benefits [occur] when you combine aerobic exercise plus resistance training," which agrees with the current recommendations, Dr. Church commented. It also sheds light on a potential mechanism to explain why exercise works, he added.
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What is HbA1c?
The term HbA1c refers to glycated haemoglobin. It develops when haemoglobin, a protein within red blood cells that carries oxygen throughout your body, joins with glucose in the blood, becoming 'glycated'.
By measuring glycated haemoglobin (HbA1c), clinicians are able to get an overall picture of what our average blood sugar levels have been over a period of weeks/months.
For people with diabetes this is important as the higher the HbA1c, the greater the risk of developing diabetes-related complications.
HbA1c is also referred to as haemoglobin A1c or simply A1c.
How does HBA1c return an accurate average measurement of average blood glucose?
When the body processes sugar, glucose in the bloodstream naturally attaches to haemoglobin.
The amount of glucose that combines with this protein is directly proportional to the total amount of sugar that is in your system at that time.
Because red blood cells in the human body survive for 8-12 weeks before renewal, measuring glycated haemoglobin (or HbA1c) can be used to reflect average blood glucose levels over that duration, providing a useful longer-term gauge of blood glucose control.
If your blood sugar levels have been high in recent weeks, your HbA1c will also be greater.
HbA1c targets
Targets for HbA1c are as follows:
- For people without diabetes, the range is 20-41 mmol/mol
(4-5.9%) - For people with diabetes, an HbA1c level of 48 mmol/mol
(6.5%) is considered good control, although some people may prefer their numbers to be closer to that of non-diabetics - For people at greater risk of hypoglycemia (lower than normal blood sugar), a target HbA1c of 59 mmol/mol (7.5%) to reduce the risk of hypos
| HbA1c targets | mmol/mol | % |
|---|---|---|
| Non-diabetics | 20 - 41 mmol/mol | 4% - 5.9% |
| Diabetics | 48 mmol/mol | 6.5% |
| Diabetics at higher risk of hypoglycemia | 59 mmol/mol | 7.5% |
Type 2 diabetes is a really interesting disorder to study because it presents problems with glucose metabolism. Many people that are insulin resistant or in a state of prediabetes will also have similar problems but to a lesser degree. Problems with glucose metabolism often mean it is quite difficult to lose weight. So anything that can reverse this and aid glucose metabolism will help with weight control.
The study shows improvements in HbA1c related to increased fitness and reduced waist circumference generally.
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