What is Diabetes?
Diabetes mellitus is a syndrome of impaired glucose metabolism caused by a complete or partial deficiency of the hormone, insulin, and/or decreased sensitivity of the body’s tissues to insulin. This results in hyperglycemia – elevated blood glucose levels. The metabolism of fats and protein are also affected in diabetes mellitus as well as the water and electrolyte balance in the body.
The pancreas contains a group of tissue known as the islet of Langerhans. It has three types of cells in it – alpha, beta and delta cells. The beta cells secrete insulin, as well as amylin. When glucose enters the bloodstream, the pancreas releases insulin, and this decreases the blood glucose level by the following ways :
- Acts on the cells membranes and promotes glucose uptake and usage.
- Liver cells take up glucose, convert it to glycogen and store it.
A lack of insulin or decreased sensitivity of the body’s tissues to respond to insulin means that the glucose will continue to circulate in the bloodstream leading to elevated blood glucose levels (hyperglycemia).
Apart from glucose, insulin affects the fat and protein in the body :
- Once the maximum glycogen capacity is reached, the liver will convert the excess glycogen into fatty acids.
- Proteins synthesis is promoted and breakdown (catabolism) is decreased.
The serious, and often life-threatening effects of diabetes is seen in the long term. The disruption of nutrient metabolism has far reaching consequence for various organs in the body and affects the functioning and structure of these areas. This is most pronounced in the the blood vessels. This derangement eventually leads to the complications of diabetes, especially in the eye, nervous system and kidneys.
What Causes Diabetes?
There are various causes of diabetes which either disrupt insulin production or impair the cell’s ability to take up glucose as it become less sensitive to insulin (insulin resistance). A genetic predisposition is a common risk factor among all types of diabetes and obesity has become a growing concern as it is linked to both type 2 and gestational diabetes. Individual causes and risk factors are discussed under each type of diabetes.
Types of Diabetes Mellitus
There are three main types of diabetes :
- Type I (1) diabetes
- Type II (2) diabetes
- Gestational diabetes
Type 1 Diabetes
This type of diabetes is often called juvenile-onset diabetes mellitus because it tends to start at a younger age, usually around the age of 14 years, although it may develop earlier or later in life. Type 1 diabetes is a result of destruction of the beta cells in the pancreas thereby impairing insulin production.
Types 1 diabetes is an autoimmune disease which means that they body’s immune cells attack and destroy the beta cells. There are various theories about the causes of this immune dysfunction but the exact cause in every case is unknown. It is believed that there is a hereditary tendency (genetic/inherited) for the beta cells to degenerate and prevent the immune cells from attacking it. This may also be linked to viruses or environmental factors.
Type 1 diabetes tends to develop very abruptly, over days or weeks. The destruction of the beta cells is extensive and little or no insulin is produced therefore insulin needs to be administered (injection).
Type 2 Diabetes
This type of diabetes is also known as adult-onset diabetes because it tends to occur later in life, usually after the age of 30. These days however, type 2 diabetes is being seen in younger age groups, even in adolescents.
With type 2 diabetes, the impairment of glucose metabolism arises as a result of a decreased sensitivity to insulin by the body’s cells. This means that the cells do not respond to insulin to take up glucose from the bloodstream and utilize it. This is known as insulin resistance. Unlike in type 1 diabetes, the insulin levels in the blood are elevated, above the norm (hyperinsulinemia) as the pancreas secretes higher amounts of glucose in an attempt to overcome this resistance (compensatory mechanism).
Type 2 diabetes has been linked to a number of factors, of which obesity (especially the accumulation of abdominal fat) is now considered as the main risk factor. The rising incidence of obesity globally, especially in children and young adults, may account for type 2 diabetes being seen in younger age groups than was previously the case. Other factors that contribute to the development of type 2 diabetes includes a family history of diabetes, previous history of gestational diabetes (pregnant women), sedentary lifestyle and ethnicity.
Insulin resistance may also be caused by the following :
- High amounts of glucocorticoids (high doses or long term use of corticosteroids, Cushing’s syndrome)
- Excess growth hormone
- Polycystic ovary syndrome (PCOS)
- Autoantibodies to the insulin receptor
- Mutations of the insulin receptor (genetic or acquired)
- Hemachomatosis – iron overload
Type 2 diabetes develops gradually as the cells resistance to insulin increases over time. Despite the resistance, the cells do take up glucose but in much smaller quantities and only in the presence of very high levels of insulin. Eventually the beta cells become “exhausted” and insulin production and secretion drops.
This type of diabetes develops in some women in late pregnancy and usually resolves after the birth of the baby. It can however persist and become permanent. Even if gestational diabetes resolves, the mother is at an increased risk of type 2 diabetes as mentioned above. The baby is also at a higher risk of type 2 diabetes if born to a mother who had gestational diabetes.
The main causes of gestational diabetes appear to be related to the hormone fluctuations associated with pregnancy as well as excessive weight gain during pregnancy. Obese women who fall pregnant are at a greater risk as well as certain ethnic groups and women who were diagnosed with pre-diabetes (impaired glucose tolerance) prior to pregnancy.
Apart from increasing the baby’s risk of developing type 2 diabetes later in life, gestational diabetes may also increase body fat in the baby (large baby requiring cesarean section), cause low blood sugar levels (hypoglycemia) in the baby or breathing problems (neonatal breathing problems).
Article reviewed by Dr. Greg. Last updated on October 15, 2010