Page 17 - The SA Journal Diabetes & Vascular Disease Volume 9 No 4 (November 2012)

VOLUME 9 NUMBER 4 • NOVEMBER 2012 159
SA JOURNAL OF DIABETES & VASCULAR DISEASE CHANGING BEHAVIOUR
Table 1. What the guidelines say
• Adults should take at least 150 minutes of at least moderate intensity
physical activity a week, in bouts of 10 minutes or more
• One option is 30 minutes of moderate activity on at least five days a
week
• Another alternative is 75 minutes of vigorous intensity activity spread
across the week
• Adults should undertake physical activity to improve muscle strength on at
least two days a week
• Everyone should minimise the amount of time they spend being sedentary
for extended periods
in low-income households and in black or minority ethnic groups, apart from
African-Caribbean and Irish populations. And self-reported measures of sed-
entary behaviour show two-thirds of adults spend more than two hours each
day watching TV and using a computer.
WHAT’S THE EVIDENCE THAT PHYSICAL ACTIVITY
PREVENTS CVD?
There is strong evidence that physical activity prevents the development
of coronary artery disease (CAD) and reduces further events and symp-
toms in patients with established CVD. People who are physically ac-
tive have a 20–35% lower risk of cardiovascular disease, coronary heart
disease and stroke compared to those who are sedentary. Prospective
epidemiological studies consistently show that the most physically active
people have half the coronary artery disease (CAD) rates of the most
sedentary. The mechanisms by which physical activity reduces CAD are
also clear. Studies show beneficial effects of exercise on atherosclerotic
risk factors, myocardial function, coronary artery size and capacity to
vasodilate, vascular tone and vulnerability to ventricular fibrillation.
The underlying effect of physical activity is anti-inflammatory, produc-
ing antioxidants that remove damaging free radicals, so preventing the
tissue damage that leads to a whole range of diseases, according to
Dr Bird. “Physical activity is the most effective anti-ageing treatment we
have,” he says, adding that this is a simple message to give to patients
to help get them moving.
THE EVIDENCE FOR PHYSICAL ACTIVITY IN TYPE 2 DIABETES
Physical activity has long been considered a cornerstone of diabetes man-
agement, together with diet and medication. But high-quality evidence on
its benefits in diabetes has only emerged over the past few years.
First, exercise can reduce the risk of progression to diabetes. Two ran-
domised trials have shown that taking
around 150 minutes of physical ac-
tivity a week and diet-induced weight
loss of 5–7% more than halved the
risk of progression from impaired
glucose tolerance (IGT) to
type 2 diabetes, with
a 58% reduction. An-
other study showed
that exercise alone,
diet alone and exer-
cise and diet com-
bined were all equally
effective in reducing
progression from IGT
to diabetes.
What about the effects of exercise on people who already have type 2
diabetes? Studies show that structured exercise programmes have a sta-
tistically and clinically significant beneficial effect on glycaemic control.
A systematic review of trials of more than eight weeks’ duration showed
HbA1c was, on average, around 0.6% lower in people taking regular ex-
ercise compared to controls (7.65% vs 8.31%). This reduction was inde-
pendent of weight loss.
Larger cohort studies have found that higher levels of regular physical
activity are associated with significantly lower cardiovascular and overall
mortality in people with type 2 diabetes than can be explained by glucose
lowering alone. One study showed that men in the lowest quartile of
cardiorespiratory fitness had 4.5-fold greater risk for overall mortality
than those in the highest quartile, even after adjusting for other risk fac-
tors including fasting glucose and underlying CVD.
HOW MUCH IS ENOUGH?
The updated guidelines for physical activity, published in 2011, recom-
mend that adults should take at least 150 minutes of at least moderate
intensity physical activity a week, in bouts of 10 minutes or more (see
Table 1). One way to achieve this, the guidance suggests, is to do 30
minutes on at least five days a week.
What counts as moderate intensity? Options include brisk walking and
moderate pace cycling (see Table 2). An easy way to explain moderate
intensity activity to patients is to say that it should make them breathe
faster, experience an increase in heart rate and feel warmer. They may
even sweat on warm days.
Alternatively, the guidelines suggest comparable benefits can be
achieved through 75 minutes of vigorous intensity activity spread across
the week. A person doing vigorous activity will usually be breathing very
hard, have a rapid heartbeat and not be able to carry on a conversation
comfortably.
Adults should undertake physical activity to improve muscle strength
on at least two days a week, because this helps maintain functional abil-
ity, keeps bones healthy, and is beneficial for glucose metabolism and
blood pressure, and everyone should minimise the amount of time they
spend being sedentary for extended periods.