Observational studies have shown that overweight, obesity, and excess abdominal fat are directly related to cardiovascular risk factors, including high levels of total cholesterol, LDL-cholesterol, triglycerides, blood pressure, fibrinogen, and insulin (86), and low levels of HDL-cholesterol (42). Plasminogen activator inhibitor-1 causing impaired fibrinolytic activity is elevated in persons with abdominal obesity (763). Overweight, obesity, and abdominal fat are also associated with increased morbidity and mortality from CHD (11, 42, 155-161).
Recent studies have shown that the risks of nonfatal myocardial infarction and CHD death increase with increasing levels of BMI. Risks are lowest in men and women with BMIs of 22 or less and increase with even modest elevations of BMI. In the Nurses' Health Study, which controlled for age, smoking, parental history of CHD, menopausal status, and hormone use, relative risks for CHD were twice as high at BMIs of 25 to 28.9, and more than three times as high at BMIs of 29 or greater, compared with BMIs of less than 21 (90). Weight gains of 5 to 8 kg (11 to 17.6 lb) increased CHD risk (nonfatal myocardial infarction and CHD death) by 25 percent, and weight gains of 20 kg (44 lb) or more increased risk more than 2.5 times in comparison with women whose weight was stable within a range of 5 kg (11 lb) (90). In British men, CHD incidence increased at BMIs above 22 and an increase of 1 BMI unit was associated with a 10 percent increase in the rate of coronary events (162). Similar relationships between increasing BMI and CHD risk have been shown in Finnish, Swedish, Japanese, and U.S. populations (90, 163, 164).
A relationship between obesity and CHD has not always been found. Two reasons may account for this: the first is an inappropriate controlling for cholesterol, blood pressure, diabetes, and other risk factors in statistical analysis and the second is that there was an inadequate controlling for the confounding effect of cigarette smoking on weight (88). People who smoke often have a lower body weight but more CHD.