Diabetes mellitus is a metabolic disorder that occurs due to either a deficiency of insulin or insulin action or both. It raises blood glucose levels (hyperglycaemia), which may affect the eye, kidney, nerves and blood vessels.
Normal blood gluose varies in humans between 70-100mg/dl in the fasting state and 100 -140 mg/dl in the fed state. Glucose is the principal fuel for energy in the body. The main source of blood glucose is food that is digested and absorbed from the gut. The other source is stored carbohydrate i.e. glycogen in the liver and muscle. In the fed state body mainly depends on glucose derived from the ingested food. In the fasting state the body maintains blood glucose by breakdown of stored glucose especially from the liver (glycogenolysis).
This delicate balance of blood glucose throughout 24 hours is maintained accurately by the action of insulin which is secreted from the beta cell of the pancreases irrespective of the eating pattern and physical activity. Another important determinant of maintaining blood glucose is the sensitivity of the insulin action on the muscle, fat and liver tissues. When insulin sensitivity is decreased, body needs more insulin to burn glucose to produce energy. This is called insulin resistance.
Insulin resistance is commonly seen in obese people who have more fat in the body and in the muscle. When this delicate balance is affected body will not be able to use (metabolise) glucose and there will be accumulation of blood glucose. This state of increased blood glucose level is called Diabetes Mellitus.
Causes of Diabetes:
Ageing populations, economic development, urbanization, unhealthy diets, increased sugar consumption, low fruit, low vegetable intake and reduced physical activity are generally associated with diabetes.1 There are many modifiable factors and Non modifiable factors which cause diabetes. They include the following
- Genetic predisposition
- Obesity or overweight
- Central obesity
- Sedentary life style
- Unhealthy diet
- Mental and physical stress
- Multiple pregnancies
- Gestational Diabetes mellitus
Stages of Diabetes:
Diabetes develops and progresses because of loss of beta-cell function. UKPDS clearly shows loss of 50% of beta-cell function at the time diagnosis, which continued to decline, progress and worsen diabetes. This is shown in the graph below,2
In early stages of development of diabetes, insulin resistance is compensated by increased insulin secretion. This causes higher than normal blood levels of insulin (Phase 1). Insulin resistance in due course tends to worsen so that postprandial hyperglycemia develops despite elevated insulin concentration (Phase 2). Over a period of time, as the pancreatic beta cells get exhausted, it’s secreting capacity decreases. This results in lower insulin secretion and diabetes develops (Phase 3). As blood glucose rises, this in turn causes further reduction in insulin secretion (glucotoxicity). Presence of insulin resistance, decreased insulin secretion and glucotoxicity produces a decompensated state of glucose metabolism leading to Diabetes Mellitus.3
- World Health Organization, Food and Agriculture Organization UN. Diet, nutrition and the prevention of chronic diseases: report of a joint WHO/FAO expert consultation. Geneva: World Health Organization; 2002 – WHO technical report series; 916
- Lebovitz HE. Diabetes Review 1999; 7: 139- 153
- Gordon C. Weir and Susan Bonner-Weir; Five Stages of Evolving Beta-Cell Dysfunction During Progression to Diabetes; DIABETES, VOL. 53, SUPPLEMENT 3, DECEMBER 2004; S16-21