Derrick Garwood, Freelance Medical Writer and Editor

Metabolic syndrome is a disorder that has come a long way in a short time. Although the individual signs and symptoms have been known for many years, it was first defined by the World Health Organisation (WHO) only seven years ago, yet will soon overtake cigarette smoking as the number one risk factor for heart disease in the USA. The good news is that the syndrome can be effectively countered by improved diet, exercise and weight loss.

Stay on this page if you want a detailed academic account of the condition, but if you are looking for something more easily digestible, try the American Heart Association site. Metabolic syndrome, or syndrome X, consists of a group of metabolic risk disorders in a single individual; these include abdominal obesity, insulin resistance, blood fat disorders, hypertension, a prothrombotic state and a proinflammatory state. Sufferers are at increased risk of coronary heart disease and other conditions related to atherosclerosis (e.g. stroke and peripheral vascular disease), as well as type 2 diabetes. The syndrome is becoming increasingly common in the United States as obesity levels rise dramatically, and more than 50 million US citizens are now thought to have it. There are no universally accepted criteria for diagnosing the syndrome, but the definitions devised by the WHO and the US National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) can be found here.

The dominant factors in this condition tend to be abdominal obesity and insulin resistance. Fat distributed around the waist (abdominal or android obesity) is classically found in men and is associated with a range of disease processes, unlike the gynoid distribution typical in women. Abdominal obesity may be quite apparent (!), and it is quantified by calculating the Waist-Hip-Ratio (WHR). The waist at its narrowest point is divided by the hip circumference at its widest, both measured while the individual is standing. Ratios above 0.8 in females and 0.95 in males are considered to increase the risk of disease. This may be because abdominal fat cells are more likely to break down and release free fatty acids than those in other locations. Abdominal fat has three compartments: visceral, retroperitoneal and subcutaneous. Some studies have indicated that visceral fat is most strongly correlated with risk factors, while other suggest that subcutaneous fat is most closely linked to insulin resistance.

In individuals with insulin resistance, extra insulin must be released by the pancreas to overcome the resistance and enable glucose to enter tissue cells. This can result in simultaneously elevated insulin and glucose concentrations in the bloodstream. Over time, raised glucose levels can damage blood vessels, and abnormalities of the coronary arteries have been demonstrated in young adults with insulin resistance but no other risk factors for heart disease.

Although there is a genetic element, obesity is the most common cause of insulin resistance. Excess fat interferes with the ability of muscles to utilise insulin, and this is compounded by lack of exercise. People with levels of glucose that are higher than normal but do not reach the diabetic range are said to have 'pre-diabetes', and studies have shown that the majority will go on to develop type 2 diabetes within 10 years if they do not reduce their body weight by 5% to 7%. There is a simple, patient-orientated description of type 2 diabetes here but a more detailed clinical perspective can be found on the emedicine site. This makes the point that for type 2 diabetes to develop there must be both peripheral insulin resistance and an insulin-secretory defect. It also states that about 90% of sufferers are obese and all overweight individuals have insulin resistance. Moreover, type 2 diabetes is no trifling matter; in the US, diabetes is the major cause of blindness in adults aged 20 to 74, as well as the leading cause of non-traumatic lower-extremity amputation and end-stage renal disease.

In addition to cardiovascular disease and type 2 diabetes, a four-year prospective study concluded that elderly people with metabolic syndrome and high inflammation (elevated levels of C-reactive protein and interleukin-6) are at greater risk of cognitive decline.

The consumption of dairy products has been linked to a reduced risk of metabolic syndrome, possibly as a result of the calcium content, but much research appears to suggest that the best way to avoid it is to adhere to the Victorian concept of clean living and temperance (!). A pattern of heavy alcohol consumption seems to increase the risk, especially if it is established early in life, while even passive smoking multiplies the risk five-fold in adolescents and young adults. Teenage smokers are approximately six times more likely to develop the condition, and the risk is greater if they are overweight. It has even been demonstrated that eating at fast-food restaurants more than twice a week is associated with more weight gain and insulin resistance. Sarsaparilla and a good book, anyone?

This tour was submitted by Derrick Garwood, a Freelance Medical Writer and Editor.

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