Metabolic syndrome is the name given to a group or cluster of conditions that occur together and increase a person's risk of diabetes, heart disease, and stroke. A short definition of the syndrome is that it is a group of metabolic risk factors found concurrently in one individual. Metabolic syndrome is also known as insulin resistance syndrome, cardiometabolic syndrome, hypertriglyceridemic waist, syndrome X, and Reaven's syndrome, after the California diabetes researcher who first described it in 1992.
Using the standards proposed by the National Cholesterol Education Program (NCEP) and the American Heart Association (AHA) in 2017, doctors think that about a sixth, or 47 million adults in the United States have metabolic syndrome. Because the risk of developing the syndrome increases as people get older, some researchers think the true rate among US adults may be as high as 25%, or 47 million people. Among Hispanic adults, it is thought to be as high as 31%. With regard to seniors, metabolic syndrome is thought to affect 44% of the US population over age 50, with women at greater risk than men. Researchers expect the rate of metabolic syndrome to increase over the next few decades as the rate of obesity among children as well as adults continues to rise.
Metabolic syndrome is a growing problem worldwide as well in North America. About a quarter of the adult population of Europe and Latin America is estimated to meet the criteria for metabolic syndrome. East Asian countries such as China, Japan, and South Korea also report recent increases in the proportion of the population with metabolic syndrome.
Metabolic syndrome has been recognized since the 1970s as a cluster of risk factors associated with diabetes, but it has only been intensively studied since the 1990s.
As the many names given to metabolic syndrome indicate, it has been defined somewhat differently by various public health organizations and medical societies since it was first named syndrome X by Dr. Gerald Reaven in 1992. Reaven was initially concerned with the relationship of the syndrome to insulin resistance, a condition in which a person's body cannot use the insulin produced by the pancreas effectively. Although insulin resistance is not considered a disease by itself, it is known to increase a person's risk of developing type 2 diabetes and heart disease. Dr. Reaven later wrote a book for the general public about the connection between syndrome X and heart disease.
In 1999, the World Health Organization (WHO) published a set of guidelines for identifying metabolic syndrome that included being diagnosed with type 2 diabetes as well as insulin resistance, high blood pressure, and obesity. More recent definitions of the syndrome, however, do not require that a person be diagnosed with diabetes, and instead emphasize that metabolic syndrome is a collection or group of conditions that increase a person's risk of serious illness, rather than being a disease in its own right. The National Cholesterol Education Program (NCEP) and modified by the American Heart Association (AHA) distinguished between the metabolic risk factors of the syndrome itself—abnormally high levels of blood cholesterol, high blood pressure, and high levels of sugar in the blood—and what the two groups called the underlying risk factors. These risk factors include obesity, insulin resistance, aging, not getting enough exercise, and hormonal imbalances.
To be identified as having metabolic syndrome according to the NCEP/AHA standards, an adult must have three or more of the following conditions:
Although it is possible for a person to have only one of these health problems, having any of them increases the risk of developing the others.
Although the causes of metabolic syndrome are not fully understood as of 2018, what is known is that some people are more likely than others to develop the syndrome. These risk factors include:
There is no general consensus about the cause or causes of metabolic syndrome, though there is widespread agreement among researchers that it is the end result of a complicated series of changes in the body's metabolism. The changes in body functions contributing to and resulting from the syndrome are highly complex and not yet fully understood. Some researchers think that obesity is the basic cause of metabolic syndrome, while others think that insulin resistance is the basic cause. A third group of doctors think that both obesity and insulin resistance are the results of a more general metabolic disturbance in a person's body caused by a combination of genetic and environmental factors. For example, recent population studies indicate that the rate of insulin clearance in a person is highly determined by genetic factors. Emotional stress, excessive blood clotting, and systemic low-grade inflammation have also been discussed as possible causes. As of 2018, research was continuing into the possible causes of the metabolic syndrome in general and insulin resistance in particular.
It is possible for people to develop metabolic syndrome over a period of years without any noticeable symptoms; this slow development is one reason why regular medical checkups are important to good health. In addition, some people develop metabolic syndrome without being obese or having a large waist measurement. Most people with metabolic syndrome are diagnosed in the course of a medical checkup that includes a blood test.
In some cases, people with diabetes that have not yet been diagnosed may notice increased thirst; increased urination, especially at night; unusual tiredness; and blurred vision. High blood pressure usually develops without any symptoms; however, a few people with hypertension may notice dull headaches, dizzy spells, or more nosebleeds than usual.
Some people are diagnosed with insulin resistance, one of the risk factors for metabolic syndrome, because they develop a skin condition called acanthosis nigricans. A person with acanthosis nigricans develops dark patches on the skin of the neck or on the elbows, knees, knuckles, or armpits. This skin discoloration is more common in Hispanics or African Americans with insulin resistance.
Because metabolic syndrome usually does not present the kinds of symptoms that lead people to see a doctor and because it is more likely to affect older adults, doctors are now recommending that adults be screened for the syndrome starting at age 45. If the results of blood tests and other measurements are normal, screening should be repeated only every three years. If the person has any risk factors in addition to age, the doctor will usually recommend screening more frequently, depending on the number of other risk factors and their severity.
Screening for metabolic syndrome consists of first measuring the patient's waist at the top of the upper edge of the hipbone just after the person has exhaled. The doctor will also weigh the patient, note the distribution of body fat, and measure the patient's blood pressure. A sample of blood will be taken and sent to a laboratory to measure the levels of triglycerides and cholesterol.
The patient's blood sugar level and possible insulin resistance can be tested in two ways. The first is a fasting blood glucose test. The person is instructed to not eat or drink anything (except water) after midnight the evening before the test, and then has a sample of blood drawn in the morning. The second test is called a glucose tolerance test and measures how quickly the body uses sugar. In the glucose tolerance test, the person has one sample of blood drawn after fasting overnight and the second sample taken two hours after drinking a sugary liquid in the doctor's office or diagnostic laboratory. Blood sugar levels higher than normal but not high enough to indicate type 2 diabetes are considered a sign of pre-diabetes.
A pre-diabetes score on the fasting blood glucose test and the glucose tolerance test is considered indirect evidence of insulin resistance. To measure insulin resistance directly, a doctor must use a complicated test called the euglycemic clamp, which is usually done only by scientists in research laboratories. The euglycemic clamp test takes about 2 hours. The patient is given an intravenous solution of insulin and a solution of glucose (sugar). The patient's blood sugar level is measured every 5 to 10 minutes. The amount of intravenous glucose that the patient needs during the last 30 minutes of the test to maintain a normal level of blood sugar measures the person's sensitivity to insulin. If the patient needs high levels of additional glucose, they are considered insulin sensitive. Very low levels indicate insulin resistance.
Metabolic syndrome is treated first with a combination of lifestyle changes. The goal is to lower the patient's risk of heart disease and type 2 diabetes by bringing blood pressure, blood sugar, and blood cholesterol down to healthier levels. If the patient has already been diagnosed with type 2 diabetes, treatment is focused on lowering the risk of heart disease. Specific lifestyle changes include:
Some patients need medications in addition to lifestyle changes to treat specific health risks associated with the metabolic syndrome. The specific drugs prescribed and their dosages depend on the individual patient's test results. Prescribed medications include:
Acanthosis nigricans may be treated with topical preparations containing Retin-A, 20% urea, or salicylic acid; however, many patients find that the skin disorder improves following weight loss.
The metabolic syndrome by itself does not require surgical treatment; however, patients who have already developed heart disease may require coronary artery bypass surgery. In addition, very obese patients—those with a BMI of 40 or higher—may benefit from bariatric surgery. Bariatric surgery includes such procedures as vertical banded gastroplasty and gastric bypass, which limit the amount of food that the stomach can contain.
The only herb or plant that has been used in a clinical trial as a treatment for metabolic syndrome as of 2018 is bitter gourd (Momordica charantia L.), also called bitter melon, a vine that is widely grown in Asia, Africa, and parts of the Caribbean for its edible fruit. While the 42 subjects in the experimental study group appeared to benefit from dietary supplementation with the plant, the authors noted that further studies are needed. Complementary interventions that have recently been reported to benefit women at risk for metabolic syndrome due to obesity or PCOS are acupuncture and yoga.
Dietary recommendations for metabolic syndrome are intended to help a person lose weight and attain a body mass index (BMI) of 25 or less (a BMI of 26 to 29 is considered overweight; a BMI of 30 or above is considered obese). The “heart-healthy” diet recommended by the National Heart, Lung, and Blood Institute (NHLBI) emphasizes the following foods:
Though metabolic syndrome is not itself a disease, meaning that it does not have its own prognosis, it is a risk factor for type 2 diabetes, heart disease, and stroke. According to the NHLBI, a person with metabolic syndrome has twice the risk of developing heart disease and five times the risk of developing type 2 diabetes as a person without the syndrome. Other disorders associated with metabolic syndrome include nonalcoholic fatty liver disease and obstructive sleep apnea.
With regard to obesity associated with the metabolic syndrome, the Centers for Disease Control and Prevention (CDC) states that obese adults have a 10%–50% increase in their risk of dying from any cause, compared to people whose weight is normal or only slightly overweight. Obesity shortens a person's life expectancy by 6–7 years on average and accounts for 112,000 excess deaths each year in the United States compared to people of normal weight. Men with a BMI over 40 have their life expectancy shortened by 20 years, and women by 5 years.
Some risk factors for metabolic syndrome, such as age, race, and family history, cannot be changed. People can, however, lower their risk of developing metabolic syndrome by following guidelines from the National Heart, Lung, and Blood Institute:
See also Açaí berry ; American Diabetes Association ; Chromium ; CSIRO total wellbeing diet ; Diabetes mellitus ; Diabetic diet ; Gestational diabetes ; Grapefruit diet ; Hypertriglyceridemia ; Insulin ; Mediterranean diet ; Sugar ; TLC diet .
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Centers for Disease Control and Prevention, 1600 Clifton Rd. NE, Atlanta, GA, 30333, (800) CDC-INFO (232-4636), TTY: (888) 232-6348, firstname.lastname@example.org, http://www.cdc.gov .
National Diabetes Information Clearinghouse, 1 Information Way, Bethesda, MD, 20892-3560, (800) 860-8747, TTY: (866) 569-1162, Fax: (703) 738-4929, email@example.com, http://diabetes.niddk.nih.gov .
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Rebecca J. Frey, PhD