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Conditions That Contribute To Diabetes

The conditions described below are often a component of diabetes (especially of Type 2 syndrome) and may themselves contribute to the existence of the condition.

Insulin Resistance

We have already seen that resistance to the effects of insulin, which usually appears to act at the level beyond the receptor sites, is of major significance in Type 2 diabetes. Insulin resistance is defined as a reduced response or sensitivity to a physiological amount of insulin (i.e. a quantity which would be expected to have an identifiable effect). Its existence is suspected when a test of a venous blood plasma sample after a fast reveals an abnormally high level of insulin (hyperinsulinaemia) in the presence of a normal or raised level of blood glucose. Sensitivity to insulin can be determined using a laboratory technique called the hyperinsulinaemic glucose clamp. A certain quantity of insulin is infused and at the same time, dextrose (a form of sugar) is also given. The more sugar that is required to maintain a normal blood glucose level during the period of elevated insulin caused by the infusion, the greater the person's sensitivity to insulin. Studies suggest that there is considerable variation in the degree of insulin sensitivity in apparently healthy people, and insulin resistance as such does not cause any symptoms. Indeed, about one quarter of those surveyed have degrees of insulin resistance comparable with those in people diagnosed with glucose intolerance or Type 2 diabetes.

Insulin Resistance Syndrome

This syndrome was first described in 1988 and has a number of alternative names (Reaven's syndrome, metabolic syndrome, syndrome X). It has several components and usually more than one is present in those affected. The key features, identified in 1988, are:

glucose intolerance or Type 2 diabetes
decreased level/rate of glucose disposal by insulin
hyperinsulinaemia-
essential hypertension (high blood pressure)
low plasma levels of HDL lipoproteins
hypertriglyceridaemia (high levels of triglyceride fats in the blood).

Since 1988, other factors have been added which were felt to be important, including abdominal obesity and impaired fibrinolysis - a process that normally takes place in the blood by means of which minute blood clots are broken down. Insulin resistance syndrome confers a much greater risk of atherosclerosis or furring of the arteries and coronary heart disease. People with Type 2 diabetes or impaired glucose tolerance quite often show features of the syndrome (such as hypertension) . It is necessary to treat these conditions, alongside diabetes, when they are present in order to reduce the risk of cardiovascular disease.

Polycystic Ovary Syndrome and Insulin Resistance

In women, the relatively common condition called polycystic ovary syndrome, in which the follicles of the ovaries fail to produce eggs to maturity and develop multiple small cysts, may in some cases be linked with insulin resistance, in some cases. Polycystic ovary syndrome is caused by a hormonal imbalance which results in a greater than normal availability of male sex hormones [androgens, mainly testosterone) which may stimulate a masculine pattern of hair growth in some women. The ovaries normally produce minute quantities of androgens which are 'mopped up' by proteins called globulins. It is thought that hyper-insulinaemia in insulin resistance may stimulate the production of testosterone by the ovaries and also inhibit the production of globulin. This allows more testosterone to be available, producing the symptoms of polycystic ovary syndrome. It has been found that affected women may have a greater susceptibility to Type 2 diabetes. Also, women affected by gestational diabetes run a greater risk of developing polycystic ovary syndrome.

Abdominal (or Visceral) Obesity

As has been noted, there is a close connection between obesity and Type 2 diabetes and it is thought that upper body or abdominal fat may be particularly important. However, although men are more likely to show this pattern of fat distribution than women (who more frequently lay down fat below the waist), there is no apparent sex difference in the incidence of Type 2 diabetes. The main function of abdominal adipocytes (fat cells) is to store triglycerides as an energy reserve in times of need. These fat cells have been shown to have a different metabolic activity compared to other fat cells elsewhere, particularly with regard to their sensitivity to certain hormones. They have been found to be more resistant to insulin but show greater sensitivity to catecholamines (counter-regulatory hormones) which act in opposition to insulin. Hence it is felt by some experts that abdominal obesity promotes the type of insulin resistance that is often a feature of Type 2 diabetes, although it is probably only one contributory factor and may not be enough to cause diabetes in itself.

Hypertension

High blood pressure can occur on its own but it is often a feature of Type 2 diabetes and the insulin resistance syndrome. Less commonly, it may also be associated with Type 1 syndrome as well. It is believed that the physiological and metabolic consequences of insulin resistance and Type 2 diabetes promote the development of hypertension and that the two are closely linked.

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