Type 2 diabetes is caused by varying degrees of insulin resistance and insulin deficiency.
Insulin resistance is a condition in which the cells of the body become resistant to the effects of insulin ie. the normal response to a given amount of insulin is reduced. Hence higher levels of insulin are needed to have the effects on the cells.
It is thought that the initial development of type 2 diabetes starts with impaired insulin action or insulin resistance.
Insulin resistance causes certain physiological responses. Therefore two defects are necessary for the development of type 2 diabetes – insulin resistance and insulin deficiency relative to the resistance ( see Figure below )
This dual defect of insulin resistance and insulin deficiency is caused by a combination of genetic and environmental factors.
Studies suggest a strong genetic basis for development of type 2 diabetes. (It has been noticed that there is almost 90% concordance rate in monozygotic twins)
In most cases the insulin resistance is due to obesity, especially the visceral fat ( which is next to the intestines ).
The proportion of visceral fat , compared to the overall fat is dependant on Genetics and ethnicity. Asians , particularly Indians have a larger proportion of visceral fats compared to other populations.
Thus Indians are more likely to develop insulin resistance and diabetes at lower levels of obesity, since they have more visceral fats.
The rising incidence of type 2 diabetes over the past few decades also suggests a link to the lifestyle of people.
Increased consumption of higher fat foods and decreased physical activity are causing increase in obesity worldwide, thereby increasing the number of people at risk for developing type 2 diabetes.
Causes of Insulin Resistance
There are several probable causes of insulin resistance, including genetic factors.
Some of them are
- Infection or severe illness
- Steroid use
Insulin Resistance and Diabetes – relationship
Insulin resistance is the first stage towards devlopment of type 2 diabetes and it is present sometimes for years.
In people who will ultimately develop diabetes, it is found that blood glucose and insulin levels are normal for years.
Then at some stage insulin resistance develops.
Further at this stage there is often an association of high insulin levels, central obesity , lipid abnormalities and/or high blood pressure ( hypertension).
This constellation of various disease processes is known as metabolic syndrome.
The Metabolic Syndrome
The key component of the metabolic syndrome is central obesity.
Metabolic syndrome is defined as central obesity plus any of the two factors shown below
- Increased trigylcerides
- Reduced HDL-cholestrol
- Increased blood pressure
- Increased fasting blood glucose
The metabolic syndrome should be treated aggressively so as to reduce the risk of cardiovascular disease and to prevent type 2 diabetes.
The recommended treatment for metabolic syndrome include promotion of a healthy lifestyle which includes
- Moderate calorie restriction to achieve 5-10% weight loss
- Moderate increase in physical activity
- Change in Diet composition
Because of insulin resistance, the muscles are resistant to insulin and therefore the pancreas needs to make more insulin to maintain a normal glucose level.
However the resistance of the cells continues to rise over time and the pancreas has to make more and more insulin to maintain normal glucose levels.
When the pancreas is no longer able to make enough insulin, the blood glucose levels begin to rise.
Initially they rise after meals, when glucose levels are at their highest and more insulin is needed, but eventually the level is high even in the fasting state.
Type 2 diabetes in now present in the body.
The ability of the pancreas to produce enough insulin may be affected by any of the following factors
- Pancreatic disease