The evidence is overwhelming that adverse lifestyle factors are the cause of type 2 diabetes, which is becoming an increasing health problem. Interestingly, the disease used to be called late onset diabetes until it became more prevalent in younger people and is now being seen in adolescents and prepubertal children. Then it was called non-insulin dependent diabetes, but as GPs know, the natural history of this disease is such that insulin is often needed as the disease progresses, so this name has also been superseded.
Type 2 diabetes usually arises because of insulin resistance in which the body fails to use insulin properly, combined with some level of insulin deficiency. It increases the level of cardiovascular (CV) disease and is a major cause of morbidity and mortality. Our main thrust of management in the past has been to treat the disease as it presents to us, usually with dietary and exercise advice as well as anti diabetic medications, which are usually needed for the rest of the patient's life and often in increasing doses.
Is it worth putting more energy into both primary and secondary prevention? Figures just reported from the first national survey of the problem in Australia show that around 7% of the population are clearly diagnosed as having type 2 diabetes and many others are pre-diabetic or undiagnosed frank diabetics. The prevalence of type 2 diabetes is expected to double in the next 10 years.
About 80% of the Australian population visit their GP in a year and 56% of the population are either overweight or obese. 80% of people with type 2 diabetes are overweight or obese. GPs are not only ideally placed to diagnose and treat diabetes, but also to intervene in the evolution of the disease, and to prevent the inevitable progression from a poor diet and inactivity to increased weight and insulin resistance, impaired glucose tolerance and on to frank diabetes with associated cardiovascular risk factors.
When thinking prevention there is always a tendency to concentrate on diet. Whilst this is important, particularly in reducing dietary fats, the overwhelming evidence is that the main cause of positive energy balance in weight gain is due to inactivity, not over consumption of calories.
Wei and associates (1) report a survey of 1,263 men who self reported their physical activity and were evaluated for physical fitness and CV risk factors. They found a strong relation between these measures of cardio-respiratory fitness and mortality that held after statistical correction of baseline differences in traditional CV risk factors such as hypertension, hyperlipidaemia, smoking and a personal or family history of CV disease. The least physically active patients (those in the lowest 20% of the fitness categories) also had most pre-existing risk factors and history of CV disease.
The value of an exercise program in the prevention of type 2 diabetes in high risk people has been researched. In the Malmo Preventive Trial (2) a prospective diet and exercise program reduced conversion from abnormal glucose tolerance to frank diabetes by one third.
The above studies only included people of European ethnicity but James et al did a study (3) of the risk for type 2 diabetes among African Americans which also demonstrated a marked reduction of risk for physically active men. So a program of increased physical exercise should help prevent the progression to frank diabetes in high risk persons, ie. those who have a family history of diabetes, history of gestational diabetes or obesity, especially in combination with high risk ethnicity such as Australian Aborigines or with abnormal fasting or post prandial glucose levels.
Another study just published by the American Diabetes Association, the Finnish diabetes prevention study (4) looked at 523 people with impaired glucose tolerance and an average BMI of 31 between 1993 and 1998. They were divided into two groups: an intervention group that had intensive dietetic and exercise advice and support and a control group that had minimal support. Of 83 cases of diabetes that developed during the study, 57 occurred in the control group and only 26 developed in the intervention group.
The cumulative incidence of diabetes after four years of study was 22% in the control group and only 10% in the study group, yielding a 58% reduction in the incidence of the disease. Equal benefits were seen in men and women.
The clinical significance of these studies for GPs is that addressing physical activity is an important part of management of type 2 diabetes. Encouraging patients to become more active is worthwhile. There also needs to be more health promotion of these preventative measures as well as addressing a broader national political approach to combat the environmental issues that produce our obesogenic environment.
References:
(1) Wei et al - Low cardiorespiratory fitness and physical inactivity as predictors of mortality in men with type 2 diabetes. Ann Intern Med. 2000, 132.605-11
(2) Eriksson KF, Lindgate F. No excess 12 year mortality in men with impaired glucose tolerance who participated in the Malmo Preventive Trial with diet and exercise. Diabetologia 1998, 41:1010-6.
(3) James et al Physical activity and NIDDM in African-Americans. The Pitt County Study. Diabetes Care. 1998;21:555-62.
(4) The Finnish Diabetes Prevention Study presented to the American Diabetes Association's 60th Annual Scientific Sessions, San Antonio (June 10, 2000)
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