Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are increased, and people may lose weight even if they are not trying to
Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high.
- Urination and thirst are increased, and people may lose weight even if they are not trying to.
- Diabetes damages the nerves and causes problems with sensation.
- Diabetes damages blood vessels and increases the risk of heart attack, stroke, chronic kidney disease, and vision loss.
- Doctors diagnose diabetes by measuring blood sugar levels.
- People with diabetes need to follow a healthy diet that is low in refined carbohydrates (including sugar), saturated fat, and processed foods. They also need to exercise and usually take drugs to lower blood sugar levels.
Diabetes mellitus is a disorder in which the amount of sugar in the blood is elevated. Doctors often use the full name diabetes mellitus, rather than diabetes alone, to distinguish this disorder from diabetes insipidus. Diabetes insipidus is a relatively rare disorder that does not affect blood glucose levels but, just like diabetes mellitus, also causes increased urination.
(See also Diabetes Mellitus in Children and Adolescents.)
The three major nutrients that make up most food are carbohydrates, proteins, and fat. Sugars are one of three types of carbohydrates, along with starch and fiber.
There are many types of sugar. Some sugars are simple, and others are complex. Table sugar (sucrose) is made of two simpler sugars called glucose and fructose. Milk sugar (lactose) is made of glucose and a simple sugar called galactose. The carbohydrates in starches, such as bread, pasta, rice, and similar foods, are long chains of different simple sugar molecules. Sucrose, lactose, carbohydrates, and other complex sugars must be broken down into simple sugars by enzymes in the digestive tract before the body can absorb them.
Once the body absorbs simple sugars, it usually converts them all into glucose, which is an important source of fuel for the body. Glucose is the sugar that is transported through the bloodstream and taken up by cells. The body can also make glucose from fats and proteins. Blood “sugar” really means blood glucose.
Did You Know…
|Blood “sugar” really means blood glucose.|
Insulin, a hormone released from the pancreas (an organ behind the stomach that also produces digestive enzymes), controls the amount of glucose in the blood. Glucose in the bloodstream stimulates the pancreas to produce insulin. Insulin helps glucose to move from the blood into the cells. Once inside the cells, glucose is converted to energy, which is used immediately, or the glucose is stored as fat or the starch glycogen until it is needed.How Insulin Works
The levels of glucose in the blood vary normally throughout the day. They rise after a meal and return to pre-meal levels within about 2 hours after eating. Once the levels of glucose in the blood return to pre-meal levels, insulin production decreases. The variation in blood glucose levels is usually within a narrow range, about 70 to 110 milligrams per deciliter (mg/dL), or 3.9 to 6.1 millimoles per liter (mmol/L) of blood in healthy people. If people eat a large amount of carbohydrates, the levels may increase more. People older than 65 years tend to have slightly higher levels, especially after eating.
If the body does not produce enough insulin to move the glucose into the cells, or if the cells stop responding normally to insulin (called insulin resistance), the resulting high levels of glucose in the blood and the inadequate amount of glucose in the cells together produce the symptoms and complications of diabetes.
Types of Diabetes
Prediabetes is a condition in which blood glucose levels are too high to be considered normal but not high enough to be labeled diabetes. People have prediabetes if their fasting blood glucose level is between 100 mg/dL (5.6 mmol/L) and 125 mg/dL (6.9 mmol/L) or if their blood glucose level 2 hours after a glucose tolerance test is between 140 mg/dL (7.8 mmol/L) and 199 mg/dL (11.0 mmol/L). Prediabetes carries a higher risk of future diabetes as well as heart disease. Decreasing body weight by 5 to 10% through diet and exercise can significantly reduce the risk of developing future diabetes.
Type 1 diabetes
In type 1 diabetes (formerly called insulin-dependent diabetes or juvenile-onset diabetes), the body’s immune system attacks the insulin-producing cells of the pancreas, and more than 90% of them are permanently destroyed. The pancreas, therefore, produces little or no insulin. Only about 5 to 10% of all people with diabetes have type 1 disease. Most people who have type 1 diabetes develop the disease before age 30, although it can develop later in life.
Scientists believe that an environmental factor—possibly a viral infection or a nutritional factor during childhood or early adulthood—causes the immune system to destroy the insulin-producing cells of the pancreas. A genetic predisposition makes some people more susceptible to an environmental factor.
Type 2 diabetes
In type 2 diabetes (formerly called non– insulin-dependent diabetes or adult-onset diabetes), the pancreas often continues to produce insulin, sometimes even at higher-than-normal levels, especially early in the disease. However, the body develops resistance to the effects of insulin, so there is not enough insulin to meet the body’s needs. As type 2 diabetes progresses, the insulin-producing ability of the pancreas decreases.
Type 2 diabetes was once rare in children and adolescents but has become more common. However, it usually begins in people older than 30 and becomes progressively more common with age. About 26% of people older than 65 have type 2 diabetes. People of certain racial and ethnic backgrounds are at increased risk of developing type 2 diabetes: blacks, Asian Americans, American Indians, and people of Spanish or Latin American ancestry who live in the United States have a twofold to threefold increased risk as compared with whites. Type 2 diabetes also tends to run in families.
Obesity is the chief risk factor for developing type 2 diabetes, and 80 to 90% of people with this disorder are overweight or obese. Because obesity causes insulin resistance, obese people need very large amounts of insulin to maintain normal blood glucose levels.
Certain disorders and drugs can affect the way the body uses insulin and can lead to type 2 diabetes.
Examples of common states (conditions) that result in impaired insulin use are
- High levels of corticosteroids (most commonly due to use of corticosteroid drugs or Cushing syndrome)
- Pregnancy (gestational diabetes)
Diabetes also may occur in people with excess production of growth hormone (acromegaly) and in people with certain hormone-secreting tumors. Severe or recurring pancreatitis and other disorders that directly damage the pancreas can lead to diabetes.Diabetes Mellitus
Symptoms of Diabetes Mellitus
The two types of diabetes can have very similar symptoms if the blood glucose is significantly elevated.
The symptoms of high blood glucose levels include
- Increased thirst
- Increased urination
- Increased hunger
When the blood glucose level rises above 160 to 180 mg/dL (8.9 to 10.0 mmol/L), glucose spills into the urine. When the level of glucose in the urine rises even higher, the kidneys excrete additional water to dilute the large amount of glucose. Because the kidneys produce excessive urine, people with diabetes urinate large volumes frequently (polyuria). The excessive urination creates abnormal thirst (polydipsia). Because excessive calories are lost in the urine, people may lose weight. To compensate, people often feel excessively hungry.
Other symptoms of diabetes include
- Blurred vision
- Decreased endurance during exercise
Type 1 diabetes
In people with type 1 diabetes, the symptoms often begin abruptly and dramatically. A serious condition called diabetic ketoacidosis, a complication in which the body produces excess acid, may quickly develop. In addition to the usual diabetes symptoms of excessive thirst and urination, the initial symptoms of diabetic ketoacidosis also include nausea, vomiting, fatigue, and—particularly in children—abdominal pain. Breathing tends to become deep and rapid as the body attempts to correct the blood’s acidity (see Acidosis), and the breath smells fruity and like nail polish remover. Without treatment, diabetic ketoacidosis can progress to coma and death, sometimes very quickly.
After type 1 diabetes has begun, some people have a long but temporary phase of near-normal glucose levels (honeymoon phase) due to partial recovery of insulin secretion.
Type 2 diabetes
People with type 2 diabetes may not have any symptoms for years or decades before they are diagnosed. Symptoms may be subtle. Increased urination and thirst are mild at first and gradually worsen over weeks or months. Eventually, people feel extremely fatigued, are likely to develop blurred vision, and may become dehydrated.
Sometimes during the early stages of diabetes, the blood glucose level is abnormally low at times, a condition called hypoglycemia.
Because people with type 2 diabetes produce some insulin, ketoacidosis does not usually develop even when type 2 diabetes is untreated for a long time. Rarely, the blood glucose levels become extremely high (even exceeding 1,000 mg/dL [55.5 mmol/L]). Such high levels often happen as the result of some superimposed stress, such as an infection or drug use. When the blood glucose levels get very high, people may develop severe dehydration, which may lead to mental confusion, drowsiness, and seizures, a condition called hyperosmolar hyperglycemic state. Many people with type 2 diabetes are diagnosed by routine blood glucose testing before they develop such severely high blood glucose levels.
Complications of diabetes
Diabetes damages blood vessels, causing them to narrow and therefore restricting blood flow. Because blood vessels throughout the body are affected, people may have many complications of diabetes. Many organs can be affected, particularly the following:
- Brain, causing stroke
- Eyes (diabetic retinopathy), causing blindness
- Heart, causing heart attack
- Kidneys (diabetic nephropathy), causing chronic kidney disease
- Nerves (diabetic neuropathy), causing decreased sensation in feet
High blood glucose levels also cause disturbances in the body’s immune system, so people with diabetes mellitus are particularly susceptible to bacterial and fungal infections.
Diagnosis of Diabetes Mellitus
- Measuring the level of glucose in the blood
The diagnosis of diabetes is made when people have abnormally high levels of glucose in the blood. Doctors do screening tests on people who are at risk of diabetes but have no symptoms.
Did You Know…
|Many people have type 2 diabetes and are not aware of it.|
Blood glucose measurement
Doctors check blood glucose levels in people who have symptoms of diabetes such as increased thirst, urination, or hunger. Additionally, doctors may check blood glucose levels in people who have disorders that can be complications of diabetes, such as frequent infections, foot ulcers, and yeast infections.
To accurately evaluate blood glucose levels, doctors usually use a blood sample taken after people have fasted overnight. Diabetes can be diagnosed if fasting blood glucose levels are higher than 125 mg/dL (6.9 mmol/L). However, it is possible to use blood samples taken after people have eaten. Some elevation of blood glucose levels after eating is normal, but even after a meal the levels should not be very high. Diabetes can be diagnosed if a random (not done after fasting) blood glucose level is higher than 199 mg/dL (11.0 mmol/L).
If you have diabetes, self-testing your blood sugar (blood glucose) can be an important tool in managing your diabetes and preventing complications. You can test your blood sugar at home with a portable electronic device called a blood sugar meter using a small drop of your blood.