The metabolic syndrome is a condition which is primarily characterised by insulin resistance and increases the risk for developing coronary heart disease and type 2 (maturity-onset) diabetes mellitus, as well as having other links with obesity and hormonal disturbances. Metabolic syndrome is an increasingly common disorder, with perhaps up to 40% of the adult population being affected in the USA.
Insulin resistance means that the body’s tissues, such as muscle and fat, become increasingly resistant to the action of the body’s own insulin. Thus, in order to overcome the poorer response of the tissues to actions such as sugar control, the pancreas has to produce extra insulin to get the desired effect. Insulin has a number of actions in the body.
Glucose: One of insulin's main roles is to regulate the sugar level in the blood. When sugar is absorbed from the gut into the blood stream, insulin stops the level from going up too high by driving the sugar out of the blood into the muscle and liver where it can be used as fuel or stored. Thus a failure of insulin action in this respect can lead to loss of blood sugar control and sometimes diabetes mellitus. The type of diabetes that comes on later in life (type 2 or maturity-onset diabetes) is virtually always associated with insulin resistance. However, insulin resistance can also be found in people who never become diabetic.
Body fat: Another role of insulin is concerned with body fat storage and fat mobilisation. Thus a lack of insulin effect (insulin resistance) on fat tissue can encourage fat deposition around the middle (central fat) and make weight loss more difficult. In turn, increasing central body weight can lead to increasing insulin resistance – a vicious circle. Whilst obesity is a common finding in patients with metabolic syndrome, it should be remembered that some patients are not obese at all.
Sex hormones: Insulin resistance may also affect sex hormone functions. Insulin resistance is a common feature of a condition known as polycystic ovarian syndrome. In this condition, insulin resistance results in an increase in male hormone (testosterone) availability and excess production of one of the female hormones (oestrone). The normal pituitary gland regulation of the ovaries is disturbed and this results in tiny cysts being formed in the ovaries rather than proper eggs. Thus patients often present with infertility, increased body weight and signs of excess male hormone such as hairiness and acne.
Coronary heart disease: Patients with metabolic syndrome are more likely to develop coronary heart disease. This is due to a number of factors seen with the syndrome, such as increased insulin levels, a disordered cholesterol profile, increased blood pressure, obesity, and of course actual diabetes.
Diabetes: Diabetes increases the risk of furring up of the arteries (atheroma or atherosclerosis), and thus increases the risk of coronary heart disease, kidney disease, nerve damage and blindness.
Cholesterol problems: Patients with metabolic syndrome often have low levels of HDL (high density) cholesterol. HDL protects the arteries from furring up. They also have high levels of triglycerides, which increase the risk of arteries furring up.
Hypertension: High blood pressure is associated with insulin resistance, and increases the risk of coronary heart disease and stroke.
Obesity: As stated above, insulin resistance causes central obesity and central obesity causes insulin resistance. Some people who inherit the tendency for type 2 diabetes actually develop the condition when their weight increases. If they can normalise their body weight, the diabetes often disappears.
Insulin resistance may be suspected in people who are gaining weight in a central distribution, are having carbohydrate cravings, or are having fatigue particularly if this occurs in mid-morning or mid-afternoon. The diagnosis of metabolic syndrome if at least 3 of the following factors are present:
- Raised fasting glucose
- Impaired glucose tolerance test
- Increased waist circumference
- Low HDL cholesterol
- Raised triglycerides
- Raised blood pressure