Every cell in the body needs a constant supply of glucose. This fuel is carried throughout the body by the blood. The blood glucose levels are carefully controlled. Hormones are chemical messengers that play the main role in ensuring that blood glucose levels are not too high, nor too low. However, various problems can arise and the blood glucose may reach abnormal levels.
What is hyperglycemia?
Hyperglycemia is the medical term for high blood glucose levels. At the other end is hypoglycemia which is abnormally low blood glucose levels. Since glucose is a sugar, hyperglycemia is also sometimes referred to as high blood sugar levels. If it is persistently high then it can damage cells throughout the body and cause permanent complications. This can eventually have fatal consequences.
The most common condition where hyperglycemia is seen is diabetes mellitus. This is the reason why diabetes mellitus is also sometimes called sugar diabetes. However, an elevation of blood glucose levels can also occur with other diseases and disorders. Despite the body’s attempts, the blood glucose levels do not return to a normal level in these conditions.
How are blood glucose levels controlled?
Glucose is sourced from the breakdown of food in the gut. Nutrients are absorbed from the gut and complex nutrients are broken down further within the body. Blood transports the glucose throughout the body. However, the blood glucose levels have to be maintained within a narrow range. This is mainly controlled by hormones from the pancreas.
There are two main hormones that regulate the blood glucose levels – insulin and glucagon. Insulin lowers blood glucose levels. It stimulates cells to increase glucose uptake from the blood and triggers the liver to store any excess glucose. Glucagon raises the blood glucose levels when it drops too low. Stored glucose (glycogen) is mobilized and proteins and fats are also used for energy production in a process known as gluconeogenesis.
How high are hyperglycemia levels?
The normal blood glucose levels depends on the timing of the last meal. The normal range for fasting blood glucose levels are 72 to 99mg/dL. Fasting refers to a period of not eating any food for at least 8 hours. The glucose levels can rise to as high as 140mg/dL up to 2 hours after eating a meal and still be considered normal.
Therefore fasting blood glucose levels of 100mg/dL and above is considered as hyperglycemia. Similarly blood glucose levels above 140mg/dL is considered as hyperglycemia, irrespective of when a person has consumed food. The acceptable blood glucose range differs for well managed diabetes mellitus.
Causes of Hyperglycemia
Prolonged hyperglycemia is one of the main consequences of diabetes mellitus. However, acute episodes may be seen in periods of stress/shock, severe infections, pregnancy, stroke and heart attacks. These non-diabetic causes of hyperglycemia need to be treated in order for the blood sugar levels to return to a normal state.
Hyperglycemia in strokes and heart attacks can negatively impact the prognosis. It may also be seen in conditions associated with growth hormone, like gigantism, as growth hormone is one of the accessory hormones (along with cortisol and epinephrine) that can raise blood sugar levels.
Raised blood glucose levels may be seen in stressful situations and severe illnesses as discussed above. It is primarily due to the action of the body’s ‘stress hormones’, epinephrine (mainly) and cortisol, which raises the blood glucose levels. Epinephrine reduces the body’s sensitivity to insulin and may also increase gluconeogenesis.
The rise in blood sugar levels is necessary for the body to have greater energy resources available for heightened states (‘fight-flight response’). The blood glucose levels return to normal once the stimulus for the stress is removed. Stress hyperglycemia should be monitored closely and reevaluated at regular intervals to exclude the possibility of diabetes mellitus.
Prolonged and persistent elevation in blood glucose levels in diabete mellitus (sugar diabetes) is the consequence of a lack of insulin (type 1 diabetes mellitus) or insulin resistance (type 2 diabetes mellitus). The condition develops gradually and is marked by associated signs and symptoms like:
- polydipsia (constant thirst)
- polyuria (large volumes of urine in a day ~ frequent urination)
- polyphagia (excessive hunger)
Over time, hyperglycemia associated with diabetes mellitus leads to tissue damage. This is most prominent in the nerves and blood vessels and leads to a host of complications. Diabetes mellitus is a chronic condition (irreversible) and proper glucose control (medication, diet and lifestyle) is essential to limit the impact of long standing hyperglycemia.
Effects of Hyperglycemia
In the short term, high blood glucose levels do not have a pronounced effect. It also does not cause lasting damage if it lasts for short periods of time. In fact a person may not be aware of the elevated blood glucose levels until it is detected with a diagnostic test. When symptomatic, hyperglycemia tends to cause increased thirst, headaches, blurred vision and frequent urination.
The effects of high blood glucose levels is mainly observed in chronic cases like diabetes mellitus. It damages cells throughout the body but the cells lining tiny blood vessels and nerves are more severely affected. This is seen in some of the complications of long term and often poorly controlled diabetes such as:
- Diabetic nephropathy is the kidney complication caused by diabetes mellitus. The filtration apparatus of the kidney is gradually damaged until kidney function is compromised. Eventually it can lead to kidney failure. Since the kidneys influence other processes like blood pressure, the effects can be far reaching.
- Diabetic neuropathy is the nerve complication caused by diabetes mellitus. The high glucose levels affects the tiny blood vessels of the nerves which limits oxygen supply to the nerve tissue. It can result in abnormal sensations from pain to numbness. Different functions within the body are also affected like bladder and bowel control.
- Diabetic retinopathy is the eye complication caused by diabetes mellitus. The tiny blood vessels of the inner eye tissue is affected. This affects blood supply to the light-sensitive tissue of the eye. Eyesight gradually deteriorates and eventually it may lead to blindness.