The Why Files The Why Files --

Metabolic syndrome: Key to diabetes, cardiovascular disease


Woman walks briskly in red windbreaker among leafless treesDiabetes epidemic expands: Blame "metabolic syndrome"?
Seems like the diabetes epidemic just won't quit. Type 2 diabetes affects almost 10 percent of American adults, and 1.5 million people get the diagnosis every year. Globally, 200 million are expected to have this grave condition by 2010...

National Cancer Institute

Diabetes is a blood-sugar disorder related to the hormone insulin, which cells need to remove sugar from the blood. A high level of blood sugar damages small blood vessels, like those in the heart, kidney and eye. The two forms of diabetes kill about 250,000 Americans per year, and cost more than $130 billion. Diabetes is the major cause of kidney failure, limb amputation, and vision loss in American adults. Diabetes at least doubles the risk of heart disease.


Type 1: Causes: autoimmune, genetic, and environmental factors. Insulin required daily. Includes 5 to 10 percent of diagnosed diabetics in United States. Symptoms: increased thirst, urination and hunger, weight loss, blurred vision, extreme fatigue.

Type 2: Risk factors: age, obesity, family history, physical inactivity, and certain ethnicities. About 80 percent are overweight or obese. Symptoms: fatigue, frequent urination, increased thirst and hunger, weight loss, blurred vision, and slow healing of wounds. Some people have no symptoms.

The explosion of diabetes mostly concerns type 2 (which used to be called "adult-onset diabetes," but now also strikes some kids). Unlike type 1, type 2 does not appear suddenly, but now seems to be the end of a process that begins with a condition called "metabolic syndrome."

In other words, type 2 diabetes is the culmination of a group of common conditions, including high blood pressure, abdominal obesity and abnormal blood levels of several fats. As the body stops responding to insulin, beta cells in the pancreas are forced to crank out more of the hormone. Type 2 does not appear until they wear out, says Richard Bergman, professor of medicine, endocrinology, diabetes and metabolism at the University of Southern California. "Metabolic syndrome leads to the need for more insulin secretion, but if the beta cells do not fail, you do not have diabetes."

U.S. incidence of diabetes (both types)
Graph charts gradual climb since 1980, then striking increase in the late 90s
From 1980 to 2005, diabetes diagnoses grew 124 percent, to 7.4 per 1000 people. The parallel increase in both lines shows that the rise is not due to an aging population. Notice the lines spiking in the 1990s? Graph: CDC

Bergman adds that almost all of the genes known to affect type 2 diabetes "are related to beta cell function," and this helps explain the pattern of disease seen in the population: Some ethnic groups, particularly Asians, African Americans and American Indians, "are not as equipped to compensate for a degree of insulin resistance, and as they become more obese, get more visceral fat, they become more at risk for type 2."

Other factors implicated in metabolic syndrome and diabetes include growing obesity, a surge in high-fat fast-foods, a sedentary lifestyle, and perhaps the rising use of high-fructose corn syrup over the last 30 years or so.

Graphic shows progression from risk factors to metabolic syndrome to type 2 diabetes to cardiovascular disease
A simplified view of the role of metabolic syndrome in disease

Cross my heart?
Metabolic syndrome also plays a major role in cardiovascular disease, and is actually as harmful to the heart as smoking two packs of cigarettes a day, says Francisco Lopez-Jimenez, a cardiologist at the Mayo Clinic in Rochester, Minn. Even as doctors dispute the significance and exact definition of metabolic syndrome, Lopez-Jimenez finds it useful. "It's still controversial as a new diagnosis... because every single component has a name already: hypertension, obesity, abnormal cholesterol."

Skeptics raise an obvious question, he admits: "What is the value of creating a new diagnosis, when everybody already has a name for these things, and the treatment is still the same?" But by unifying measurements that may seem trivial in isolation, metabolic syndrome makes a difference to patients, Lopez-Jimenez says. "If the blood sugar is a bit high, the waist circumference slightly abnormal, it would very likely qualify for metabolic syndrome, but without that term, they would not leave the office with clear sense of the risk for diabetes or cardiovascular disease. If they see everything as only mildly abnormal, they would not have a strong enough motivation to change behavior."Graph with six bars indicates the prevalence of bad signs among diabetics, including physical inactivity and problems with body weight, blood chemistry, and blood pressure

Diabetics have many of the common risk factors Graph: CDC

As a preventive cardiologist, Lopez-Jimenez stresses that metabolic syndrome is a risk factor for heart attack and stroke, not just diabetes. "Every component of metabolic syndrome has been linked to cardiovascular disease. Although some people develop heart disease without diabetes, in many cases diabetes is the intermediate point between the metabolic syndrome and heart disease."

The strong links among metabolic syndrome, cardiovascular disease and diabetes are not fully understood, says Lopez-Jimenez. "The approach has been that high blood sugar is the bad guy, but it's probably beyond that, because several studies have failed to show significant reductions in cardiovascular events just by controlling blood sugar. People with diabetes have a constellation of abnormalities. Patients with type 2 have very high insulin levels, and that in itself can affect the cardiovascular system, making the kidneys absorb more salt, making the blood pressure go up, and changing the metabolism of cholesterol." High insulin "by itself can be linked to several measures" of hardening of the arteries. (We promise to revisit this subject...)

What is metabolic syndrome?
Metabolic syndrome (AKA insulin resistance syndrome, X syndrome, diabesity), is linked to cardiovascular disease and type 2 diabetes. One common definition comes from the National Cholesterol Education Program, which includes:

bullet point Abdominal obesity: waist circumference above 35 inches (female) or 40 inches (male);

bullet pointLow level of high-density lipoprotein (HDL, or "good cholesterol");

bullet pointElevated fasting glucose test;

bullet pointInsulin resistance (the body does not respond properly to the hormone); and

bullet pointHigh blood pressure (over 130/80).

Metabolic syndrome may be grim, but it's not all gloom and doom, especially if you can control your weight and activity.

So let's get moving: Want to reverse metabolic syndrome?


Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

©2017, University of Wisconsin, Board of Regents.