Nashville Diabetes Dentist

The fluctuation of blood sugar (red) and the sugar-lowering hormone insulin (blue) in humans during the course of a day with three meals. One of the effects of a sugar-rich vs a starch-rich meal is highlighted.

Blood sugar concentration, or glucose level, refers to the amount of glucose present in the blood of a human or animal. Normally, in mammals the blood glucose level is maintained at a reference range between about 3.6 and 5.8 mM (mmol/l). It is tightly regulated as a part of metabolic homeostasis.

Mean normal blood glucose levels in humans are about 90 mg/dl, equivalent to 5mM (mmol/l) (since the molecular weight of glucose, C₆H₁₂O₆, is about 180 g/mol). The total amount of glucose normally in circulating human blood is therefore about 3.3 to 7g (assuming an ordinary adult blood volume of 5 litres, plausible for an average adult male). Glucose levels rise after meals for an hour or two by a few grams and are usually lowest in the morning, before the first meal of the day. Transported via the bloodstream from the intestines or liver to body cells, glucose is the primary source of energy for body’s cells, fats and oils (ie, lipids) being primarily a compact energy store.

Failure to maintain blood glucose in the normal range leads to conditions of persistently high (hyperglycemia) or low (hypoglycemia) blood sugar. Diabetes mellitus, characterized by persistent hyperglycemia from any of several causes, is the most prominent disease related to failure of blood sugar regulation.

Normal values

Despite widely variable intervals between meals or the occasional consumption of meals with a substantial carbohydrate load, human blood glucose levels normally remain within a remarkably narrow range. In most humans this varies from about 82 mg/dl to perhaps 110 mg/dl (4.4 to 6.1 mmol/l) except shortly after eating when the blood glucose level rises temporarily up to maybe 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).

It is usually a surprise to realize how little glucose is actually maintained in the blood and body fluids. The control mechanism works on very small quantities. In a healthy adult male of 75 kg (165 lb) with a blood volume of 5 litres (1.3 gal), 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). A more familiar comparison may help – 5 grams of glucose is about equivalent to a small sugar packet as provided in many restaurants with coffee or tea, with people using typically 1 to 3 packets per cup.

Regulation

The homeostatic mechanism which keeps the blood value of glucose in a remarkably narrow range is composed of several interacting systems, of which hormone regulation is the most important.

There are two types of mutually antagonistic metabolic hormones affecting blood glucose levels:

• catabolic hormones (such as glucagon, growth hormone, cortisol and catecholamines) which increase blood glucose;
• and one anabolic hormone (insulin), which decreases blood glucose.

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