Metabolic syndrome, also known as insulin resistance syndrome, came to prominence in the last decade when medical researchers and epidemiologists realized a cluster of factors was associated with both heart disease and diabetes.
First described in 1988 as "syndrome X," it was not until the 2000s that metabolic syndrome became widely established as a grouping of risk factors predisposing people to cardiovascular disease, as well as type 2 diabetes.1-5
The factors agreed as features of metabolic syndrome have evolved considerably, but the general consensus is that having at least 3 of the following 5 factors should trigger a diagnosis:1-5
- Central, visceral, abdominal obesity, as indicated by a big waist
- Raised blood glucose levels
- High blood pressure (hypertension)
- High blood levels of triglycerides (fat molecules)
- Abnormal blood levels of cholesterol, with low levels of high-density lipoprotein (HDL).
Having three or more of these factors signifies a higher risk of cardiovascular diseases, such as heart attack or stroke, and type 2 diabetes, which used to be considered a late-onset disorder but is increasingly seen in younger people with these risk factors.
Not all medical guidelines agree on the exact thresholds to use for a diagnosis of metabolic syndrome - and doctors will always consider a patient's individual circumstances - but most settle on the following for the five factors mentioned above:
- Waist size of 40 inches or over in men, or 35 inches or over in women (at least 102 cm or 88 cm respectively)
- Blood glucose raised to a fasting plasma level of 100 mg/dL (5.6 mmol/L) or higher - the same level that triggers a diagnosis of "prediabetes"
- Blood pressure of 130/85 mm Hg or higher
- Triglycerides raised to a fasting blood plasma level of 150 mg/dL (1.7 mmol/L) or higher
- HDL below 40 mg/dL in men, or below 50 mg/dL in women (below 1.04 mmol/L or 1.29 mmol/L respectively).
Metabolic syndrome rising with childhood obesity6,8
Metabolic syndrome, sometimes seen abbreviated to MetS, starts in childhood alongside early obesity, dyslipidemia and high blood pressure, but the thresholds for diagnosis, and whether children should be screened for these, remain controversial. Growing children show wide variance in these factors, for example.
Excess fat in childhood is a major cardiometabolic risk factor for disease in later life.
Nonetheless, many describe an urgent global need to identify those children and adolescents at higher cardiovascular risk, to target changes toward a healthier lifestyle and reduce the adult disease burden.
Driving the concern in particular is the rise in the levels of children being overweight or obese.
One study tracking the obesity epidemic in children in semirural Bogalusa, LA, for example, found that high obesity levels have persisted following an alarming rise in the late 2000s compared with the early 1970s.
Trends in body mass index (BMI), from data for more than 11,000 children and adolescents aged 5 to 17 years, show a rise from 14.2% in 1973-1974 to 48.4% in 2008-2009 for the proportion measured as overweight or obese. This was more than a tripling of the problem.
Over the same period, the proportion of children and adolescents specifically measured as obese rose from 5.6% to 30.8%.
Since metabolic syndrome is a collection of risk factors, it does not itself have a single cause.
While being centrally obese or overweight is the major factor leading to metabolic syndrome, the other factors of abnormal blood lipid and cholesterol profiles, high blood pressure and prediabetes also create cardiometabolic risk.
Big waistlines indicate high central obesity - a major cardiometabolic risk factor.
There are unavoidable risk factors, such as family history and ethnic background, that can lead to a higher risk of some components of the syndrome, but all of its factors also share lifestyle as a common root.
As mentioned above, the increasing problem of childhood obesity is a major contributor to the lifestyle problem behind metabolic syndrome. Obesity across all age groups is extremely common in developed countries, where many are consuming too much energy while leading sedentary lives.
The prevalence of obesity in the US, for example, may be over 40% of people who are more than 50 years of age.
The insulin resistance characteristic of the metabolic syndrome and obesity can lead to cardiovascular disease and type 2 diabetes (learn more about this link from MNT's detailed page on insulin resistance), but other conditions are also linked to insulin resistance: polycystic ovary syndrome (PCOS), nonalcoholic fatty liver disease and chronic kidney disease.
Other problems that are sometimes associated with metabolic syndrome, insulin resistance and high blood sugar are low-level inflammation and blood clotting defects - these can also contribute to the development of cardiovascular disease.
One of the aims of doctors in following metabolic syndrome is to identify those people whose waistline size - visceral/central/abdominal excess fat (adipose tissue) - puts them at a particular cardiovascular and diabetes risk but who can be targeted for lifestyle modification rather than the drug treatments used at the later stages of illness.
Eating healthily and increasing physical activity are measures for losing weight and managing metabolic syndrome.
The diagnostic levels are such that people with metabolic syndrome typically do not yet have the conditions that necessitate direct medical intervention. High blood glucose levels, high blood pressure and lipid and cholesterol abnormalities are typically first targeted with lifestyle measures.
Having said this, the syndrome can still exist when certain elements are already under medical treatment because drug treatment for any of the components of metabolic syndrome can also count in the diagnosis. For example, taking antihypertensive or anticholesterol drugs counts as having, respectively, the blood pressure and cholesterol risks that can define the condition.
The most important aspect of managing metabolic syndrome with lifestyle modifications is reducing the upper body distribution of excess fat - the obesity problem that needs to be treated by losing weight.
Find out more from the following MNT pages:
- How much should I weigh? - includes information on various measures of obesity, including BMI, waist-to-hip ratio and body fat percentage
- How to lose weight - how to adjust diet and exercise and lose the high-risk fat tissue.
For the treatment and prevention of abnormal cholesterol, the following measures can also help against the other risk factors in the metabolic syndrome:
- Eating a "heart-healthy diet"
- Taking regular exercise
- Avoiding smoking and reducing alcohol intake.
The main focus of treatment is lifestyle modification, but drug treatment can also be utilized, typically involving metformin. This strategy is recommended by the American Diabetes Association for certain higher-risk groups, namely patients with higher blood glucose levels and greater obesity.
Metformin is a drug usually reserved for the treatment of type 2 diabetes in people who do not succeed with diet and exercise alone, and is sold under the following brand names in the US:
The drug is not officially licensed for preventive use in people who have a high risk of diabetes because of metabolic syndrome. However, some doctors do prescribe it for diabetes prevention in people with raised glucose levels and abdominal obesity, doing so "off-label" with the recommendations of diabetes specialists and evidence from clinical trials.
A randomized trial of such preventive use, published in the New England Journal of Medicine in 2002, provided data to support this strategy, although only in conjunction with lifestyle measures, which were more effective than an up to twice-daily dose of metformin for reducing the chances of developing type 2 diabetes.
Metformin is prescribed only after lifestyle measures have been tried, and diet and exercise changes should be maintained while the drug is used.
In fact, diet and exercise were highly effective, with the trial showing that one case of diabetes was prevented for every seven people treated for 3 years when lifestyle measures were followed.
The prevention program was intensive, involving the following:
- Lifestyle intervention to lose at least 7% of initial body weight, and keep it off, by following
- A healthy, low-calorie, low-fat diet, and doing
- Physical activity of moderate intensity, such as brisk walking, for at least 150 minutes a week.
The participants following this lifestyle program in the trial were supported by a 16-lesson course to teach them about diet, exercise and behavior modification. It was taught on a one-to-one basis for the first 24 weeks, and then individual and group sessions were used monthly for the remainder of the 3 years.
Other drugs may also be used in treating metabolic syndrome, such as statins in certain people at higher risk because of high levels of low-density lipoprotein (LDL) cholesterol. High blood pressure may also be treated with antihypertensive drugs. Again, for both these uses of drugs, lifestyle measures are tried first or in lower-risk groups.