The blood sugar concentration or blood glucose level is the amount of glucose (sugar) present in the blood of a human or animal. Normally, in mammals the body maintains the blood glucose level at a reference range between about 3.6 and 5.8 mM (mmol/L, ie, millimoles/liter) (64.8 and 104.4 mg/dL). It is tightly regulated as a part of metabolic homeostasis.
Glucose is the primary source of energy for body's cell, lipids (in the form of fats and oils) being primarily a compact energy store. It is transported from the intestines or liver to body cells via the bloodstream, and is absorbed by body cells with the intervention of the hormone insulin normally produced by the body.
The mean normal blood glucose level in humans is about 4 mM (4 mmol/L or 72 mg/dL, ie milligrams/deciliter). However, the glucose level fluctuates during the day. It rises after meals for an hour or two by a few grams and is usually lowest in the morning, before the first meal of the day (termed "the fasting level").
When a blood sugar level is outside the normal range, it may be an indicator of a medical condition. A persistently high level is referred to as hyperglycemia or if low as hypoglycemia. Diabetes mellitus is characterized by persistent hyperglycemia from any of several causes, and is the most prominent disease related to failure of blood sugar regulation. A temporary elevated blood sugar level may also result from severe stress, such as trauma, stroke, myocardial infarction, or surgery; and also from illness. Alcohol, after an initial surge in blood sugar, tends to cause blood sugar to fall. Also, certain drugs can increase or decrease glucose levels.
Glucose is the primary source of energy for body's cell, lipids (in the form of fats and oils) being primarily a compact energy store. It is transported from the intestines or liver to body cells via the bloodstream, and is absorbed by body cells with the intervention of the hormone insulin normally produced by the body.
The mean normal blood glucose level in humans is about 4 mM (4 mmol/L or 72 mg/dL, ie milligrams/deciliter). However, the glucose level fluctuates during the day. It rises after meals for an hour or two by a few grams and is usually lowest in the morning, before the first meal of the day (termed "the fasting level").
When a blood sugar level is outside the normal range, it may be an indicator of a medical condition. A persistently high level is referred to as hyperglycemia or if low as hypoglycemia. Diabetes mellitus is characterized by persistent hyperglycemia from any of several causes, and is the most prominent disease related to failure of blood sugar regulation. A temporary elevated blood sugar level may also result from severe stress, such as trauma, stroke, myocardial infarction, or surgery; and also from illness. Alcohol, after an initial surge in blood sugar, tends to cause blood sugar to fall. Also, certain drugs can increase or decrease glucose levels.
Blood glucose measurement units
In the United States, and most other places, mass concentration, measured in mg/dL (milligrams per decilitre), is typically used.[2] In other countries, blood glucose levels are reported in terms of a molar concentration, measured in mmol/L (millimoles per litre; or millimolar, abbreviated mM).
Since the molecular weight of glucose C6H12O6 is about 180 g/mol, for the measurement of glucose, the difference between the two scales is a factor of 18, so that 1 mmol/L of glucose is equivalent to 18 mg/dL.[3]
Since the molecular weight of glucose C6H12O6 is about 180 g/mol, for the measurement of glucose, the difference between the two scales is a factor of 18, so that 1 mmol/L of glucose is equivalent to 18 mg/dL.[3]
Normal values
Many factors affect a person's blood sugar level. A body's homeostatic mechanism, when operating normally, restores the blood sugar level to a narrow range of about 82 to 110 mg/dL (4.4 to 6.1 mmol/L).
Despite widely variable intervals between meals or the occasional consumption of meals with a substantial carbohydrate load, human blood glucose levels normally remain within the normal range. However, shortly after eating the blood glucose level may rise temporarily up to 140 mg/dL (7.8 mmol/L) or a bit more in non-diabetics. The American Diabetes Association recommends a post-meal glucose level less than 180 mg/dl (10 mmol/L) and a pre-meal plasma glucose of 90–130 mg/dL (5 to 7.2 mmol/L).[4]
The actual amount of glucose in the blood and body fluids is very small. The control mechanism in the human body works on very small quantities of glucose. In a healthy adult male of 165 lb (75 kg) with a blood volume of 1.3 gal (5 litres), a blood glucose level of 100 mg/dL or 5.5 mmol/L corresponds to about 5 g (0.2 oz or 0.002 gal, 1/500 of the total) of glucose in the blood and approximately 45 g (1½ ounces) in the total body water (which includes more than merely blood and will be usually about 60% of the total body weight in men). (Small sugar packets provided in many restaurants with coffee or tea are about 2.8 grams each.
Despite widely variable intervals between meals or the occasional consumption of meals with a substantial carbohydrate load, human blood glucose levels normally remain within the normal range. However, shortly after eating the blood glucose level may rise temporarily up to 140 mg/dL (7.8 mmol/L) or a bit more in non-diabetics. The American Diabetes Association recommends a post-meal glucose level less than 180 mg/dl (10 mmol/L) and a pre-meal plasma glucose of 90–130 mg/dL (5 to 7.2 mmol/L).[4]
The actual amount of glucose in the blood and body fluids is very small. The control mechanism in the human body works on very small quantities of glucose. In a healthy adult male of 165 lb (75 kg) with a blood volume of 1.3 gal (5 litres), a blood glucose level of 100 mg/dL or 5.5 mmol/L corresponds to about 5 g (0.2 oz or 0.002 gal, 1/500 of the total) of glucose in the blood and approximately 45 g (1½ ounces) in the total body water (which includes more than merely blood and will be usually about 60% of the total body weight in men). (Small sugar packets provided in many restaurants with coffee or tea are about 2.8 grams each.
Health effects
If blood sugar levels drop too low, a potentially fatal condition called hypoglycemia develops. Symptoms may include lethargy, impaired mental functioning, irritability, shaking, twitching, weakness in arm and leg muscles, pale complexion, sweating, paranoid or aggressive mentality and loss of consciousness. Brain damage is even possible.
If levels remain too high, appetite is suppressed over the short term. Long-term hyperglycemia causes many of the long-term health problems associated with diabetes, including eye, kidney, heart disease and nerve damage.
Low blood sugar
Some people report drowsiness or impaired cognitive function several hours after meals, which they believe is related to a drop in blood sugar, or "low blood sugar". For more information, see:
idiopathic postprandial syndrome
hypoglycemia
Mechanisms which restore satisfactory blood glucose levels after hypoglycemia must be quick and effective, because of the immediately serious consequences of insufficient glucose; in the extreme, coma, but also less immediately dangerous, confusion or unsteadiness, amongst many other symptoms. This is because, at least in the short term, it is far more dangerous to have too little glucose in the blood than too much. In healthy individuals these mechanisms are generally quite effective, and symptomatic hypoglycemia is generally only found in diabetics using insulin or other pharmacological treatment. Such hypoglycemic episodes vary greatly between persons and from time to time, both in severity and swiftness of onset. For severe cases, prompt medical assistance is essential, as damage (to brain and other tissues) and even death will result from sufficiently low blood glucose levels.
If levels remain too high, appetite is suppressed over the short term. Long-term hyperglycemia causes many of the long-term health problems associated with diabetes, including eye, kidney, heart disease and nerve damage.
Low blood sugar
Some people report drowsiness or impaired cognitive function several hours after meals, which they believe is related to a drop in blood sugar, or "low blood sugar". For more information, see:
idiopathic postprandial syndrome
hypoglycemia
Mechanisms which restore satisfactory blood glucose levels after hypoglycemia must be quick and effective, because of the immediately serious consequences of insufficient glucose; in the extreme, coma, but also less immediately dangerous, confusion or unsteadiness, amongst many other symptoms. This is because, at least in the short term, it is far more dangerous to have too little glucose in the blood than too much. In healthy individuals these mechanisms are generally quite effective, and symptomatic hypoglycemia is generally only found in diabetics using insulin or other pharmacological treatment. Such hypoglycemic episodes vary greatly between persons and from time to time, both in severity and swiftness of onset. For severe cases, prompt medical assistance is essential, as damage (to brain and other tissues) and even death will result from sufficiently low blood glucose levels.
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