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Moderate activity reduces diabetes risk

Systematic review
Results
Comment

Hands up everyone who knows what a MET is? Answer is a Metabolic Equivalent Task, which is the amount of energy expended in performing various activities compared with sitting down doing nothing. It is commonly used in medicine to express metabolic rates measured during a treadmill test. Two definitions of the MET are used, essentially equivalent:

1 MET is equivalent to a metabolic rate consuming 3.5 millilitres of oxygen per kilogram of body weight per minute.

1 MET is equivalent to a metabolic rate consuming 1 kilocalorie per kilogram of body weight per hour.

In more common parlance, a slow walk or promenade is equivalent to about two METs, a brisk walk about four METs, and gym work more like six METs and above. A new systematic review of observational studies links moderate periods of moderate intensity exercise with reduced risk of developing type 2 diabetes in adults [1].

Systematic review

The review sought observational studies up to March 2006 associating moderate exercise with incidence and prevalence of type 2 diabetes. Moderate intensity exercise was that with a MET score of 3-6.

Results

Ten cohorts were found with just over 300,000 persons of both sexes aged mostly between their late-30s to early-60s. Follow up in these studies tended to be long with seven of the studies longer than seven years, and the shortest four years. The mean follow up period, weighted by study numbers, was 8.2 years.

In most of the studies exercise included walking, but cycling and light gardening were also included. The definition of diabetes varied, including glucose tolerance test results, the use of primary care or national registers, and, mostly, by self-report of a diagnosis by a physician, usually validated.

There were 9,400 cases of diabetes, a prevalence of 3.1%. This meant that type 2 diabetes occurred in 0.4% of these older adults every year, a risk of 1 in 263 per year. Compared with sedentary persons, the risk was substantially lower in people who took moderate exercise (by about 30%), whether all activity or only brisk walking was used in the tests of association (Table 1). Because people who take no exercise tend to be fatter, there was adjustment of risk for BMI, and here the reduction of risk was about 17%.



Table 1: Evidence associating physical activity and walking with reduction in risk of developing type-2 diabetes



Observation
Studies
People
Relative risk
Percent risk reduction
Total physical acitivity
Development of type 2 diabetes, no BMI adjustment
9
213,314
0.69 (0.58 to 0.83)
31
Development of type 2 diabetes, with BMI adjustment
9
295,231
0.83 (0.76 to 0.90)
17
Walking
Development of type 2 diabetes, no BMI adjustment
4
152,698
0.70 (0.58 to 0.84)
30
Development of type 2 diabetes, with BMI adjustment
4
234,615
0.83 (0.75 to 0.91)
17


Comment

The amount of exercise examined in this paper was not heroic, amounting to no more than about 2.5 hours of brisk walking every week. The message is that to help avoid developing diabetes, you don't necessarily have to go into the gym, just walk down there and then walk back again. Given that walking does other good things positively affecting heart, and circulation, and bone, and balance, and weight, this is something of a no-brainer. Diabetes is worth avoiding.

References:

  1. CY Jeon et al. Physical activity of moderate intensity and risk of type 2 diabetes. Diabetes Care 2007 30: 744-752.

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