Lifestyle Interventions to Prevent Diabetes
Bandolier
readers are familiar with the associations of weight, sedentary lifestyle, and
poor diet with type 2 diabetes in older adults, and increasingly with younger
adults and even children. Most readers would instantly prescribe diet and
exercise, but would probably not have the numbers immediately to hand to press
home any arguments about whether diet and exercise worked or not. A new
systematic review and meta-analysis [1] provides them.
Systematic review
The
review set out to answer the question whether a lifestyle education programme
compared with conventional education improved glucose levels or incidence of
diabetes in people at high risk of developing type 2 diabetes. Two outcome
measures were sought. The change in glucose values two hours after a 75 g oral
glucose load at baseline, and more than six months later. The other outcome was
diabetes incidence. Subjects had to have impaired glucose tolerance, impaired
fasting glucose, or borderline values, according to standard criteria.
Trials
had to be randomised, and searching was limited to English language papers
published to November 2004.
Results
Nine
studies were included, eight with information on plasma glucose, and five on
diabetes incidence. Seven involved diet and exercise, and two diet alone;
controls were generally conventional counselling or advice. Trials enrolled 80
to 3,000 subjects, with follow up from six months to six years; five larger
trials had follow up of three years or longer.
The
average age of patients in the trials ranged from 39 to 57 years, and the
average BMI from 24 to 31 kg/sq m. Baseline two hour plasma glucose after oral
load averaged 8-10 mmol/L in individual studies.
Plasma glucose
The
prime end point was the difference between the two hour plasma glucose from
baseline to one year or more. Results for individual studies are in Figure 1.
Overall, there was a reduction in two hour plasma glucose after an oral load by
0.8 mmol/L (95% confidence interval 0.4 to 1.3 mmol/L).
Figure 1: Change in plasma glucose at 2 hours after oral load from baseline to one year
Diabetes incidence
The
incidence of diabetes reported in five studies lasting one to six years is
shown in Figure 2. The weighted mean duration was 3.6 years. The incidence of
diabetes was 28% with control (7.8%, or 1 in 13 per year), but only 15% with
diet and exercise (4.2%, or 1 in 24 per year). The relative risk was 0.6 (0.5
to 0.7), and the number needed to treat was 7.4 (6.2 to 9.4) to prevent one
person developing type 2 diabetes.
Figure 2: Incidence of diabetes over one to six years (mean 3.6 years)
Comment
This
is good evidence, with consistent reductions both in glucose levels and in
diabetes incidence over reasonably long periods of time. The reduction of
diabetes incidence by half may even understate the case. While the average
duration was commendably long, at 3.6 years, continued use of a healthy
lifestyle should continue to generate benefits. A 10-year NNT can be calculated
at 2.6, for instance.
Put
another way, if people in the studies continued to develop diabetes at the same
rate, after 10 years 8 out of 10 in the control group would have developed
diabetes, compared with only 4 out of 10 with the intervention. And of course,
we have no information about adherence, so we only know about the effects of
treatment on average. It is likely that individuals who really changed their
lifestyle and stuck to it could reduce their individual risk of developing
diabetes to much lower levels. The message is, yet again, that the best way of
avoiding seeing your doctor, except socially, is to eat fruit and vegetables,
have a good walk, and perhaps enjoy a nice glass of wine when you get back.
Reference:
- K Yamaoka, T Tango. Efficacy of lifestyle education to prevent type 2 diabetes. A meta-analysis of randomized controlled trials. Diabetes Care 2005 28: 2780-2786.