Epidemiology
Coronary heart disease is the most common cause of morbidity and mortality
in the developed world. More than 500,000 deaths a year are attributed to
coronary heart disease in the US. At least a third of the individuals that die
of coronary heart disease are younger than 55 years of age. This disease costs
the US over 100 billion dollars per year in medical treatment and lost income.
One of the primary risk factors for heart disease is hyperlipidemia, also
prevalent in the US and throughout the developed world. Moreover, as
inhabitants of the developing world now begin to have access to more fats in
their diets and to lead more sedentary lives, the disease will become an
increasing problem there as well. The increased intake of saturated fats and
decreased intake of complex carbohydrates and foods high in fiber predispose a
person to hyperlipidemia. A sedentary lifestyle contributes to the prevalence
and severity of the dysmetabolic syndrome that includes increases in total and
LDL cholesterol and also low HDL cholesterol, insulin resistance,
hyperinsulinemia, hyperglycemia, obesity, and hypertension. These factors
contribute to the prevalence and severity of the clinical sequelae of
hyperlipidemia, including coronary heart disease.
Serum total and LDL cholesterol are continuous predictor variables that
confer risk across a broad range (including some values in the 'normal' range).
Low HDL cholesterol is associated with an increased risk of coronary heart
disease, even in the absence of elevated LDL cholesterol. This absolute risk of
disease is modified by the presence or absence of additional cardiovascular risk
factors. These risk factors include age, gender, family history, hypertension,
smoking, and diabetes mellitus. Hyperlipidemia, hypertension, and smoking are
modifiable risk factors. It remains unclear whether diabetes mellitus and low
HDL cholesterol are truly modifiable risk factors, although recent evidence
suggests that correction of these metabolic abnormalities confers a small
reduction in cumulative risk. The cumulative risk resulting from the presence
of more than one risk factor is multiplicative and not simply additive.
Figure 1.1: MRFIT and coronary heart disease risk factors and their contribution
to cumulative risk.
