Distribution of dehydroepiandrosterone sulfate and relationships between its level and serum lipid levels in a rural Japanese population.

Dehydroepiandrosterone sulfate (DHEAS) is a major secretory product of the adrenal glands. DHEAS is inversely associated with death from cardiovascular disease in males, but not in females. This cross-sectional study examined the relationships between serum DHEAS levels and atherosclerosis in free living subjects in Japan. We measured the serum DHEAS levels of 990 apparently healthy subjects aged 35-81 years old in a rural area in Japan; 431 males and 559 females. The levels were determined by the radioimmunoassay method. The frequency distribution was skewed to a lower value in both sexes. Both unadjusted and age-adjusted mean DHEAS levels were statistically higher in males than in females, A marked linear decline of levels with age was observed in both sexes. DHEAS levels were positively correlated with high density lipoprotein-cholesterol (HDLC), and negatively correlated with low density lipoprotein-cholesterol (LDLC) even after adjustment for age in both sexes. The mean atherogenic index (AI) was significantly inversely correlated with the rise of tertiles of the DHEAS level, both before and after adjustment for age, Total cholesterol (TC), HDLC and Triglyceride (TG). These results suggest high levels of serum DHEAS may have an inhibitory effect on the development of atherosclerosis and have an important role in its etiology and prevention.

been observed in several studies and proposed as an index of aging 3). The etiological role of DHEAS in the development of atherosclerosis and coronary heart disease has been suspected for more than 30 years 4). Retrospective studies have shown lower DHEAS levels in male survivors of myocardial infarction compared with controls 5), and an inverse relation of DHEAS with the extent of atherosclerosis in men 6). A few prospective studies 7,8) have suggested that DHEAS is an independent risk factor for atherosclerosis disease such as myocardial infaction. Barrett-Comer et al7). reported an independent inverse relation between plasma DHEAS and the subsequent 12-years cardiovascular or ischemic heart disease mortality rates in a prospective study of 752 men aged 50 to 79 years. In Japan, studies have shown that serum DHEAS were higher in normal subjects than in patients with essential hypertension 9). The author also reported that age-adjusted serum DHEAS levels significantly decreased with number of factors chosen as risk factor of cardiovascular disease such as body mass index, smoking, drinking, blood pressure in a free living subjects in Japan 10). And the author found a significantly negative association between serum DHEAS and atherosclerosis in 90 males workers in Japan 11). However, in a relatively large healthy Japanese population, few reports are available on the distribution of the serum DHEAS level and the relationship with serum lipids or atherosclerosis, except that serum DHEAS level declined with advancing age 12).
Therefore, the purpose of this study is to show not only the distribution of the serum DHEAS level, but also the its relationship with serum lipids in a free living subjects in Japan .

MATERIALS AND METHODS
The subjects for this study were 1789 males and females aged 35-81 years, who participated in these mass medical examinations conducted since 1983 in accordance with the health and medical service law for aged in Japan, during the 2 months from June through July in 1996, in a rural town, north of Nagoya. The distribution of the total population in this distinct and the subjects by sex and age are shown in Table 1. The participation rate of subjects to the total population was 68 percent for males and 72 percent for females. Of these persons, 510 were excluded from the present analysis, 415 (23.2 percent) because of missing data on serum levels of DHEA, and 232 (13.0 percent) because of missing data on any serum levels of total cholesterol (TC), triglyceride (TG) and high-density lipoprotein cholesterol (HDLC). Also 152 (8.5 percent) were excluded because of missing data on age, height or weight. These exclusions left 431 males and 559 females (55.3 percent of 1789 subjects) for analysis. Medical history , habitual food intake, smoking habits, alcohol consumption and physical activity were determined by a self-administered, structured questionnaire.
Height and body weight were measured with the participants wearing light clothing without shoes. Body mass index was calculated as weight (kg) /height(m)2.
Blood sanples were obtained before noon after an overnight fast from the antecubical vein and separated immediately after collection.
Serum DHEAS levels were measured by radioimmunoassay method 13). The serum levels of total cholesterol (TC) and triglyceride (TG) were determined by enzymatic methods. High-density lipoprotein cholesterol (HDLC) was measured by    Figure 2. Mean serum DHEAS levels by sex and age category. Table 4. Percentiles for serum DHEAS levels (n,g/dl) by sex. percentile of DHEAS levels were higher in males than in females.
Crude and age-adjusted correlations coefficients between logarithmic DHEAS levels and TC, TG, HDLC, and LDLC in both sexes are shown in Table 5. The crude DHEAS level was significantly inversely correlated with age and LDLC, and positively correlated with HDLC in both sexes. Even after adjustment for age, DHEAS levels were significantly positively correlated with HDLC, and significantly negatively correlated with LDLC in both sexes.  Table 6. There was a significantly linear increase in AI for increasing tertile of DHEAS level both before and after adjustment for age, TC, HDLC and TG in both sexes.

DISCUSSION
We measured DHEAS in the apparently healthy population of a rural area in Japan using a mass screening program. Some epidemioligical studies have revealed that lower DHEAS levels is a significant and independent risk factor for cardiovascular disease4-7). However, few data are available on normal range and distribution of the DHEAS level in healthy adults in both Japan and Western countries. Frequency distribution of DHEAS in this study was a skewed pattern to a lower value, which is similar to other reports 18, 19) Accordingly, we concluded that there was no difference in the DHEAS frequency distribution between Japanese and foreign adults. The mean DHEAS level in this study was similar to previous study in Japan 9, 12), but was lower than in North America or Europe 4,18,19). However, men of Japanese ancestry residing in Honolulu showed higher published levels than Japanese men residing in Japan 20). Wang observed that serum DHEAS levels among British women were higher than among Japanese women 21). We thought these differences in DHEAS levels in different geographic locations were caused by environmental rather than racial or ethnic differences.
We observed a marked linear decrease in DHEAS level with advancing age the same as previous studies in Japan and Western countries 3, 4,18,11). Metabolic studies have suggested that the decrease in DHEAS levels with age is due to decreased production of DHEAS rather than increased clearance, and is consistent with reduced adrenal activity in older men, and with enzymatic alternations with aging 22).
DHEAS has been inversely associated with cardiovascular mortality in men, but not in women. Since most of the studies on the relationships between serum DHEAS levels and cardiovascular risk factors or atherosclerosis were restricted to males, Western countries on the negative association with atherosclerosis 4,5,20). 5Some prospective studies 4,5) based on population have shown an inverse correlation between serum DHEAS levels and death from ischemic heart disease in adult men. The most compelling evidence relating the DHEAS level to coronary heart disease comes from a prospective epidemiological study of 242 men that found a threefold higher risk of coronary heart disease death over 12 years of follow-up among men with low compared to higher DHEAS levels 7). Hautanen et al 8) found , in their nested case-control study of 103 men with myocardial infarction in the Helsinki Heart Study, that cases had significantly higher levels. However, no studies have also reported the relation between serum DHEAS levels and mortality from ischemic heart disease among Japanese adult population.
We have observed that a significant inverse relation was observed between serum DHEAS and Al in our previous study used 90 males employees 14) In this cross-sectional study used more larger samples, we also found the same finding as previous study, not only in males, but also in females. Accordingly, this finding suggests that the serum DHEAS acts protective against atherosclerosis in both sexes.
Several mechanisms have been suggested for the protective action of DHEAS against atherosclerosis.
In this study, the serum DHEAS level had a significant positive association with the HDLC level which is known as a anti-atherogenic factor, and inversely association with the LDLC level, which is known as an atherogenic factor. This suggests DHEAS may indirectly inhibit the development of atherosclerosis through an increase in HDLC and a decrease in LDLC. Several studies suggest DHEAS is directly associated with the inhibition of the development of atherosclerosis. At the cellular level, DHEAS has been shown to interfere with atherogenesis by affecting adherence of platelets and macrophages, the release of chemoattractants and growth factors, the proliferation of cellular elements or uptake of cholesterol in the atheroma 23). In addition, DHEAS has been demonstrated to interfere with the generation of superoxide radicals by phorbol ester-stimulated human granulocytes.
It may be possible that DHEAS also protects against atherosclerosis by reducing local free radical generation 24). Furthermore, DHEAS is a potent non-competitive inhibitor of glucose-6 phosphate dehydrogenase, the rate-limiting enzyme of the pentose cycle, which is necessary for extramitochondrial production of reduced nicotinamide adenine dinucleotide phosphate (NADPH), a co-enzyme important in the synthesis of fatty acid, cholesterol and thromboplastin 30). Animal studies 31.32) have shown that rabbits fed high-cholesterol diets had a significant reduction in atherosclerosis plaque size in the aorta when they also received DHEAS. Fatty infiltration of the heart and liver was also markedly reduced. This study, which observed the reduction of atherosclerosis in rab-bits fed DHEAS and cholesterol, not only suggested that DHEAS inhibits the development of atherosclerosis following endotherial injury, but also is particularly strong finding that DHEAS has a direct inhibitory effect on atherosclerosis. However, the mechanism for a protective effect of DHEAS against atherosclerosis is difficult to explain only a direct inhibitory effect. Accordingly, it seems reasonable to suppose that both direct and indirect inhibitory effect with DHEAS itself play a role in the development of atherosclerosis, although it seems to be differences in the strength of inhibitory effect.
In this study, we observed that serum DHEAS levels had a significantly inversely association with age and a rise of Al in both sexes, The present findings suggest DHEAS may have a important role in the etiology and prevention of atherosclerosis in both sexes, although longitudinal follow-up studies are need to utilize the DHEAS level as an index of atherosclerosis.