VOLUME 11 NUMBER 2 • JUNE 2014
75
SA JOURNAL OF DIABETES & VASCULAR DISEASE
REVIEW
Correspondence to: CM Kolka
Department of Biomedical Sciences, Diabetes and Obesity Research
Institute, Cedars-Sinai Medical Center, CA, USA
Tel: (310) 967-2791
Fax: (310) 967-3869
e-mail:
Originally published in
Diabetes Metab
2013;
4
(9): 308
.
S Afr J Diabetes Vasc Dis
2014;
11
: 75–81
Treating diabetes with exercise: focus on the
microvasculature
CM KOLKA
Abstract
The rising incidence of diabetes and associated metabolic
diseases, including obesity, cardiovascular disease and
hypertension, have led to investigation of a number of drugs
to treat these diseases. However, lifestyle interventions,
including diet and exercise, remain the first line of defence.
The benefits of exercise are typically presented in terms of
weight loss, improved body composition and reduced fat
mass, but exercise can have many other beneficial effects.
Acute effects of exercise include major changes in blood
flow through active muscle, and an active hyperaemia
that increases the delivery of oxygen to the working
muscle fibres. Longer-term exercise training can affect the
vasculature, improving endothelial health and possibly basal
metabolic rates. Further, insulin sensitivity is improved both
acutely after a single bout of exercise and shows chronic
effects with exercise training, effectively reducing diabetes
risk. Exercise-mediated improvements in endothelial
function may also reduce complications associated with
both diabetes and other metabolic diseases. Therefore,
while drugs to improve microvascular function in diabetes
continue to be investigated, exercise can also provide many
similar benefits on endothelial function and should remain
the first prescription when treating insulin resistance and
diabetes. This review will investigate the effects of exercise
on the blood vessels and the potential benefits of exercise
on cardiovascular disease and diabetes.
Keywords:
exercise, diabetes, insulin, muscle, vasculature, blood
vessels
The prevalence of diabetes has been increasing steadily in the United
States and in many other parts of the world. In 2010, 25.8 million
individuals in the United States were diagnosed with diabetes,
a figure almost double that of 10 years previously.
1
Diabetes
frequently occurs with other diseases, including dislipidaemia,
hypertension, cardiovascular disease and obesity. Common
complications of diabetes include heart disease, blindness, kidney
disease and peripheral neuropathy, often leading to amputation.
People with type 2 diabetes are typically sedentary, overweight, and
have decreased physical fitness,
2
and the Center for Disease Control
and Prevention and the American Heart Association consider lack
of physical activity as a risk factor for heart disease.
3
Currently the first treatment prescribed for type 2 diabetes is
lifestyle modification, including diet and exercise, though drugs
are used when lifestyle changes are not sufficient. Weight loss
is a primary recommendation in overweight or obese patients,
particularly those with type 2 diabetes, and can show many short-
term benefits, such as improvements in glycaemic control, reduction
in cardiovascular risk factors, and resolution of co-existing illnesses.
Lifestyle intervention alone can cause significant weight loss and at
least a partial remission of diabetes.
4
The contribution of exercise to weight loss specifically is
controversial, and studies have shown only an incrementally
greater weight loss by exercise and diet over dietary interventions
alone. However, weight loss is not required for the resolution of
diabetes, and some drugs increase body weight while improving
insulin sensitivity, such as the thiazolidinediones.
5
Therefore obesity
and increased fat mass are not always directly linked to diabetes:
while the majority of those with type 2 diabetes are overweight, a
large proportion of obese individuals are not diabetic. Yet obesity
is a major risk factor for developing diabetes. The location of
fat tissue is a major determinant of insulin resistance, as visceral
fat is associated with insulin resistance,
6
and subcutaneous fat
deposition confers a protective effect against diabetes.
7
Obesity and
increased fat mass can determine diabetes and cardiovascular risk,
8
thus an intervention to reduce body fat will also reduce diabetes
risk. Exercise can reduce fat mass independently of changes in total
body weight.
9
Exercise is also associated with significant improvements in
other aspects of disease, such as the reduction of complications,
associated metabolic diseases, and other risk factors.
9
The metabolic
syndrome, typified by high blood pressure, high triglyceride levels,
low high-density lipoprotein (HDL) cholesterol levels, high fasting
glucose levels, and central obesity, is recognised to predispose
individuals to the development of diabetes and atherosclerosis.
Interestingly, most of the criteria of the metabolic syndrome
pertain to blood measurements, and can therefore affect blood
vessels. Further, many of the complications of diabetes, including
retinopathy, kidney disease and peripheral neuropathy, also have a
vascular basis. In their review, Joyner and Green note that exercise
is much more protective against cardiovascular disease than would
be expected based on changes in traditional risk factors, including
body mass index (BMI), blood lipid levels and blood pressure.
10
They suggest a vicious circle between autonomic dysfunction and
endothelial dysfunction, leading to cardiovascular disease, which
can be prevented by exercise.
10
Here, the role of the endothelium
and microvasculature in exercise and diabetes is reviewed.
Exercise as treatment for diabetes
Type 2 diabetes occurs when the body cannot maintain normal
blood sugar levels. In the early stages of the disease, insulin is
unable to stimulate glucose storage in the appropriate tissues. To
