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Metabolic syndrome: A risk factor for myocardial infarction and diabetes in young Britons

Gershan Davis, Erwin Rodrigues, Mahantesh Urolagin, Farhad Kaivani
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The metabolic syndrome is increasingly being recognised as a major risk factor for coronary heart disease and diabetes in the young. However, there are limited published data on this phenomenon among the young British population. We conducted an observational study and showed the presence of the metabolic syndrome and type 2 diabetes in a significant proportion of young people presenting with acute myocardial infarction. With obesity reaching epidemic proportions in the UK, our findings will be particularly relevant in the primary care setting. The identification and treatment of young Britons with the metabolic syndrome will be important in the prevention of long-term morbidity and mortality.

The metabolic syndrome comprises a constellation of risk factors associated with atherosclerotic cardiovascular disease, type 2 diabetes and their complications. The major causes of the metabolic syndrome are intra-abdominal adiposity and insulin resistance.

Differences in body-fat distribution associated with an altered metabolic profile were documented in the medical literature 50 years ago and it was dubbed Syndrome X in 1988 (Grundy et al, 2004). The World Health Organization (WHO) published the first clinical definition of the metabolic syndrome in 1998 (Alberti and Zimmet, 1998), which was revised the following year (WHO, 1999). The National Cholesterol Education Programme published a revised definition in 2002 (Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults). This was followed in 2005 by the International Diabetes Federation’s (IDF’s) definition (Alberti et al, 2005), which was most recently revised in 2006 (IDF, 2006). The IDF definition stresses the presence of central obesity in diagnosing the metabolic syndrome. 

As a result of current lifestyle choices and increasing obesity, the metabolic syndrome is becoming a major global health problem. Studies in the US have shown that more than one half of adults are obese or overweight (Centers for Disease Control and Prevention, 2008). It has been estimated that the metabolic syndrome will soon overtake cigarette smoking as the primary risk factor for cardiovascular disease (Eckel and Krauss, 1998). Grundy et al (2004) reported that the metabolic syndrome is an even stronger predictor of type 2 diabetes than traditional risk factors. However, there are very limited data published that examine the metabolic syndrome among the young British population.

Methods
We conducted an observational study over a 15-month period from September 2003 to December 2004. All young people (<45 years of age) presenting to University Hospital Aintree, Liverpool with an acute myocardial infarction, both ST segment elevation and non-ST segment elevation, were examined. Our study consisted of 68 consecutive people who fell into this category.

The IDF definition (2006) was used to determine the presence of the metabolic syndrome. Central obesity was used as the primary criterion. Where two or more of the four factors listed in Table 1 were found in addition to central obesity, the person was defined as having the metabolic syndrome. A BMI >28kg/m2 was substituted for a waist circumference ≥94cm for Europid men and ≥80cm for Europid women in the definition of obesity. This substitution is one most observers would accept as satisfactory and was previously used by Ridker et al (2003) in their analysis of the metabolic syndrome in the Women’s Health Study. 

Results and statistical analysis
Of the 68 people included in the study, 53 had all the necessary data to determine the presence or absence of the metabolic syndrome. Of these, a significant number of people (n=39, 73.6%) met the IDF criteria for having the metabolic syndrome.

Differences were found in the mean blood pressure, BMI, and fasting glucose, total cholesterol and triglyceride levels between those with and without the metabolic syndrome (Table 2). Among those with the metabolic syndrome (n=39), three (7.7%) had a history of diabetes and a further nine (23.1%) were diagnosed with diabetes at the time of presentation. Among those without the metabolic syndrome (n=14), one (7.1%) had a history of diabetes and one (7.1%) was diagnosed with diabetes at the time of presentation (Figure 1). In total, the prevalence of diabetes was more than double in those with the metabolic syndrome (30.8%) as compared to those without the metabolic syndrome (14.3%). Analysing the between group difference yielded a chi-squared value of 0.48 with a 95% confidence interval of 0.31–0.65. As the confidence interval does not contain zero, the difference between the groups is statistically significant (Table 3).

Discussion
This pilot observational study in our institution demonstrates that a significant proportion of young people with the metabolic syndrome are at high risk of acute myocardial infarction and type 2 diabetes. In the UK healthcare system, this association will have particular relevance in the primary care setting; these high-risk individuals need to be identified and treated to avoid increased risk for the associated complications. Grundy et al (2004), in their report for the American Heart Association and the National Heart, Lung and Blood Institute, state that “because of a documented high relative risk for atherosclerotic coronary vascular disease events and type 2 diabetes, the metabolic syndrome undoubtedly carries a relatively high lifetime risk for these disorders even when short term (10 years) risk is in the low to moderate range.”

Grundy et al (2005) reported that the risk for atherosclerotic coronary vascular disease associated with the metabolic syndrome is greater than the sum of its risk factors and the risk rises geometrically, not linearly. Further, they suggested that management of the metabolic syndrome is a secondary target for reducing cardiovascular events, while smoking cessation, lowering LDL-cholesterol levels and blood-pressure management are the primary targets for risk reduction. Lifestyle interventions to mitigate the modifiable risk factors, such as obesity, physical inactivity and atherogenic diet, are the initial therapies recommended for treatment of the metabolic syndrome (Grundy et al, 2005). The current available evidence suggests that individuals with the metabolic syndrome may benefit from behavioural therapy targeted towards weight loss and exercise. Knowler et al (2002) and Tuomilehto et al (2001) have both demonstrated that such lifestyle measures can reduce the risk of diabetes by up to 58%.

If lifestyle changes are not sufficient to manage the risks associated with the metabolic syndrome, drug therapies for abnormalities of the individual risk factors may be necessary. Promisingly, more recent therapies have been developed that target the possible underlying cause of the metabolic syndrome (intra-abdominal adiposity).

Our study is limited by the small number of people involved. All of the people studied were British Caucasians, and lived in the same geographical area. Reproducing this study with a larger sample size, and the involvement of a number of geographical regions, would provide valuable data on the metabolic syndrome as a risk factor for myocardial infarction and diabetes in the wider population of people aged <45 years.

Identifying young people at high risk of the metabolic syndrome in our communities is becoming increasingly important. Identifying these young people will allow healthcare professionals to initiate lifestyle interventions and therapies with the aim of decreasing long-term morbidity and mortality.

Acknowledgements
We are thankful to Mr. Steven Lane, University of Liverpool for his kind assistance with statistical analysis.

REFERENCES:

Alberti KG, Zimmet PZ (1998) Definition, diagnosis and classification of diabetes mellitus and its complications. Part 1. Diagnosis and classification of diabetes mellitus, provisional report of a WHO consultation. Diabetes Medicine 15: 539–53
Alberti KG et al for the IDF Epidemiology Task Force Consensus Group (2005) The metabolic syndrome – a new worldwide definition. Lancet 366: 1059–62
Centers for Disease Control and Prevention (2008) State-specific prevalence of obesity among adults in the United States, 2007. Morbidity and Mortality Weekly Report 57: 765–8
Eckel RH, Krauss RM (1998). American Heart Association call to action: obesity as a major risk factor for coronary heart disease. AHA Nutrition Committee. Circulation 97: 2099–100
Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (2002) Third report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults.Circulation 106: 3143–421
Grundy SM, Brewer HB, Cleeman JI et al (2004) Definition of metabolic syndrome: Report of the National Heart Lung and Blood Institute and the American Heart Association conference on scientific issues related to definition. Circulation 109: 433–8 
Grundy SM, Cleeman JI, Daniels SR et al (2005) American Heart Association and the National Heart Lung and Blood Institute: Diagnosis and management of the metabolic syndrome. Circulation 112: 2735–52
International Diabetes Federation (2006) The IDF consensus worldwide definition of the metabolic syndrome. International Diabetes Federation, Brussels
Knowler WC, Barrett-Connor E, Fowler SE et al (2002). Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. New England Journal of Medicine 346: 393–403
Ridker PM, Buring JE, Cook NR et al (2003). C-reactive protein, the metabolic syndrome, and risk of incident cardiovascular events: an 8-year follow-up of 14719 initially healthy American women. Circulation 107: 391–397
Tuomilehto J et al for the Finnish Diabetes Prevention Study Group (2001) Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. New England Journal of Medicine 344: 1343–50
World Health Organization (1999) Definition, diagnosis and classification of diabetes. World Health Organization, Geneva

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