Analysis of serum lipid levels in Japanese men and women according to body mass index. Increase in risk of atherosclerosis in postmenopausal women. Research Group on Serum Lipid Survey 1990 in Japan.

Relatively low serum lipid levels are thought to be an important factor contributing to the low incidence of ischemic heart diseases (IHD) in Japanese. It has been proven that obesity or overweight constitutes a basal condition for several risk factors in atherosclerosis. The purpose of this study is to obtain data on serum lipids and lipoprotein profiles in relation to body mass index (BMI), which will enable us to compare the nature and weight of metabolic risk factors in atherosclerosis between Japanese and people in Western countries. Data of total serum cholesterol, triglyceride, and HDL-cholesterol levels of Japanese men and women obtained from a large-scale survey in 1990 were analysed according to BMI for different age groups. Apolipoprotein A-I and B and Lp(a) were also measured in randomly selected samples and their contribution as a risk factor was estimated especially in postmenopausal women. The subjects in two age groups of men (20-39 and 40 59 years) and women (20 39 and 50-69 years) were graded into quintiles according to the BMI. The middle grades of BMI were 21.9-23.3 and 22.4-23.6 for younger and older men, and 20.0-21.1 and 22.2-23.6 for younger and older women, respectively. These values are much lower than those in Western populations, the border between the IVth and the top quintile almost corresponding to the average for Americans. Total cholesterol showed a tendency to shift into higher ranges in all age groups in both men and women as BMI increased, with the highest distribution remaining in the range of 160-199 mg/dl (4.2-5.2 mmol/l). The average cholesterol levels for the top quintile of BMI were still lower than most of the average values in Western populations. The distribution of cholesterol in higher ranges was much greater and the difference according to BMI was smaller in older women than in men. In both men and women, whether younger or older, about 90% of the subjects in the lower quintiles of BMI had triglyceride levels lower than 150 mg/dl. The distribution in the higher range of triglyceride was small in women, not only at younger ages but also in postmenopausal women at the top quintile of BMI. About 85% of the younger women with a middle grade of BMI had an HDL-cholesterol level higher than 50 mg/dl. The values in postmenopausal women were still higher than in men aged 40-59 years. Shift of the distribution curves of HDL-cholesterol according to BMI was similar in all groups and more remarkable than the change in triglyceride. The average HDL-cholesterol levels at the top quintile were almost comparable to the average values in Western countries; the difference in HDL-cholesterol levels between the two populations can mostly be explained by the difference in BMI. Smokers showed a slightly lower total cholesterol and significantly (3-4 mg/dl) lower HDL-cholesterol levels, although there was no difference in distribution of BMI between smokers and non-smokers. Relatively low total cholesterol levels even in smokers has probably contributed to the low incidence of IHD in spite of the high frequency of smoking in Japanese population. Mean Lp(a) levels showed a tendency to increase after age 40 in women. BMI itself did not have a correlation with serum Lp(a) levels. The distribution curve of Lp(a) shifted to higher levels as total cholesterol increased and the tendency was most remarkable in women around or after the menopause. It was remarkable in older women that as the total cholesterol or apo B level increased there was also an increased prevalence of abnormal ECG with a pattern of myocardial ischemia. Postmenopausal women seem to have a great risk of atherosclerosis regarding the lipid and lipoprotein profile even in the Japanese population.