Blood cholesterol : a public health perspective

Changes in total cholesterol levels (TC) were studied using data from three epidemiological studies: about 30,000 men and women aged 37-43 were examined between 1974 and 1980 (CB Project), about 80,000 men aged 33-37 between 1981 and 1986 (RIFOH Project) and 42,000 men and women aged 20-59 from 1987 to 1992 (Monitoring Project on CVD Risk Factors). In men a decline in TC of 6.5% was observed between 1974 and 1992. However, the largest decrease took place between 1981 and 1986 in men in a limited age range (33-37 years), and there were indications that this decrease was not generalizable to other age groups. From 1987 to 1992, a decrease of 7% in HDL cholesterol levels (HDL-C) was observed in men, leading to an increase in the non-HDL-C/HDL-C ratio. In women, no changes in TC and HDL-C were observed.<p>Analyses of data from 36,000 men and women aged 20-59 years showed that between ages 30 and 50 about 19-38% of the gender difference in TC was explained by differences in body mass index (BMI) and cigarette smoking between men and women. After age 50, the higher TC in women compared to men was largely due to the effect of the menopause. The TC increase associated with menopause was 0.45 mmol/l in non-smokers and 0.28 mmol/l in smokers. The difference between a low-risk and a high-risk lifestyle was 0.58 mmol/I for TC and 0.38 mmol/l for HDL-C in men, and 0.40 mmol/l for TC and 0.45 mmol/l for HDL-C in women.<p>Twelve year follow-up of 50,000 men and women aged 30-54 (CB Project) showed that the adjusted relative risk for coronary heart disease (CHD) mortality for the highest compared to the lowest cholesterol quintile was 3.0 (95% CI 1.8-5.1) in men and 3.8 (95% Cl 1.1-13.1) in women. It was estimated that a TC reduction of 0.6 mmol/l was associated with a 20% lower CHD mortality. Low TC was not associated with non-cardiovascular mortality. All-cause mortality was positively related to total cholesterol, with a 60% and 46% higher risk in the highest compared to the lowest TC quintile for men and women respectively.<p>Twenty-five year follow-up of the Seven Countries Study, in which over 12,000 men aged 40-59 at baseline participated, showed that relative risks for CHD mortality were similar in different cultures, but the absolute risks were strikingly different. At a cholesterol level of about 5.4 mmol/l agestandardized CHD mortality rates varied from 4% to 5% in Japan and Mediterranean Southern Europe to 15% in Northern Europe after adjustment for age, smoking and blood pressure. It was concluded that other factors, such as diet, typical for low-risk countries, modify the effect of TC on CHD mortality. In the Seven Countries Study, in non-smokers no association of TC with cancer mortality was observed, while non-cardiovascular/non-cancer mortality was elevated only at TC below 4.15 mmol/l. In smokers, cancer mortality and non-cardiovascular/non-cancer mortality were inversely associated with TC. All- cause mortality showed a J-shaped association with TC in non-smokers (lowest all-cause mortality for TC between 4.15 and 5.15 mmol/l), while all-cause mortality was unrelated to TC in smokers. Absolute mortality rates were higher in smokers than in non-smokers for all endpoints.<p>Lowering the average TC level in the population is concluded to contribute to a reduction in the burden of CHD. Low cholesterol levels are not considered an important public health concern in the Netherlands. Changes in the lipid profile should preferably be achieved by lifestyle interventions such as a diet low in saturated fat and rich in fruits and vegetables, no cigarette smoking, a desirable body mass index (less than 25 kg/m <sup><font size="-2">2</font></SUP>) and a physically active lifestyle. Such a lifestyle will not only have a favorable impact on coronary heart disease, but is also compatible with recommendations on the prevention of other chronic diseases such as diabetes and cancer