AIM: To demonstrate the prevalence of sonographic fatty liver, overweight and ischemic heart disease (IHD) among the male workers in Taiwan, and to investigate the possible association of these three factors.

METHODS: From July to September 2003, a total of 2 088 male aircraft-maintenance workers aged from 22 to 65 years (mean 40.5) underwent an annual health examination, including anthropometrical evaluation, blood pressure measurement, personal medical history assessment, biochemical blood analysis, abdominal ultrasonographic examination and digital electrocardiography (ECG). The Student’s t-test, χ2 test and multivariate logistic regression analysis were utilized to evaluate the relationship between IHD and salient risk factors.

RESULTS: The all-over prevalence of overweight was 41.4%, and that of fatty liver was 29.5% (mild, moderate and severe fatty liver being 14.5%, 11.3%, and 3.7%, respectively); while the prevalence of ischemic changes on ECG was 17.1% in this study. The abnormal rates for conventional IHD risk factors including hypertension, dyslipidemia, hyperglycemia and overweight increased in accordance with the severity of fatty liver. Overweight and severity of fatty liver were independently associated with increased risks for developing IHD. Overweight subjects had a 1.32-fold (95%CI: 1.01-1.73) increased IHD risk. Participants with mild, moderate, and severe fatty liver had a 1.88-fold (95%CI: 1.37-2.6), 2.37-fold (95%CI: 1.66-3.37) and 2.76-fold (95%CI: 1.62-4.72) increased risk for developing IHD. The prevalence of ischemic ECG for the fatty liver-affected subjects with or without overweight was 30.1% and 19.1%, while that of overweight subjects free from fatty liver was 14.4%. Compared to the subjects without fatty liver nor overweight, IHD risk for the three subgroups above was as follows: OR: 2.95 (95%CI: 2.31-4.09), OR: 1.60 (95%CI: 1.07-2.39) and OR: 1.11 (95%CI: 0.78-1.56), respectively.

CONCLUSION: The presence of fatty liver and its severity should be carefully considered as independent risk factors for IHD. Results of the study suggest the synergistic effect between fatty liver and overweight for developing IHD. Abdominal sonographic examination may provide valuable information for IHD risk assessment in addition to limited report about liver status, especially for overweight males.

Fatty change in the liver is closely associated with overweight status and metabolic impairments such as hyperglycemia, and dyslipidemia[1-3] which are also regarded as factors for atherosclerosis[1,4,5] and ischemic heart disease (IHD)[6-9]. However, the association between fatty liver and IHD is waiting for epidemiological investigation.

Since resting electrocardiogram (ECG) and abdominal sonographic examination are two routine, non-invasive health examinations used in medical check-ups in Taiwan[10-15], we had the opportunity to examine the association between fatty liver and ischemic ECG changes, the hallmark of IHD and strong predictor for cardiac events[16-18].

The purpose of this study was to evaluate the relationships between fatty liver and IHD utilizing epidemic data. Data analyses were controlled for conventional risk factors, especially overweight.

After 63 cases whose data were incomplete (e.g., biochemical blood test, questionnaire) were excluded, a total of 2 025 subjects were enrolled in the final analysis. The excluded subjects had a similar distribution of anthropometric measurement and biochemical data as subjects in final analysis.

As shown in Table 1, the age for this sample population ranged from 22 to 63 years (mean, 40.5), the mean value of BMI was 24.6 kg/m2. The over-all prevalence of overweight was 41.4%, while that of fatty liver was 29.5%. The prevalence of ischemic changes in the resting ECG was 17.1%. The means and standard deviations for serum blood sugar and atherogenic lipid profile were 5.7±1.1 mmol/L of fasting sugar, 5.1±0.9 mmol/L of total cholesterol, 1.3±0.3 mmol/L of HDL cholesterol, 3.3±0.8 mmol/L of LDL cholesterol, and 17.1±13.9 mmol/L of triglyceride.

Risk-factor distribution among subgroups stratified according to the severity of fatty liver, is presented in Table 2. The prevalence of mild, moderate and severe fatty liver was 14.5%, 11.3%, and 3.7%, respectively. The abnormal rates for conventional IHD risk factor including hypertension, dyslipidemia, hyperglycemia and overweight increased in accordance with the severity of fatty liver (Figure 1).

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Figure 1 Abnormal rates of IHD risk factors for middle-aged male workers in Taiwan.

Multivariable analysis and odds ratios for IHD are summarized in Table 3. Results showed that overweight, increased systolic blood pressure and fatty liver severity were independently associated with IHD risk. Overweight subjects had a 1.32-fold (95%CI: 1.01-1.73) increased IHD risk. Participants with mild, moderate, and severe fatty liver experienced a 1.88-fold (95%CI: 1.37-2.60), 2.37-fold (95%CI: 1.66-3.37), and 2.76-fold (95%CI: 1.62-4.72) increased risk for developing IHD.

The prevalence of ischemic ECG and odds ratios (OR) for IHD of the middle-aged male workers in Taiwan, stratified according to overweight and fatty liver status, are presented in Table 4. The prevalence of ischemic ECG and the risk for IHD of the fatty liver-affected subjects with or without overweight and the overweight subjects free from fatty liver was 30.1%, OR: 2.95 (95% CI: 2.31-4.09), 19.1%, OR:1.60 (95% CI: 1.07-2.39) and 14.4%, OR: 1.11 (95% CI: 0.78-1.56), respectively, compared to the subjects without fatty liver nor overweight. Result of test for interaction between fatty liver and overweight was significant (P<0.05).

Stress test or even coronary catheterization examination naturally has better specificitiy in IHD diagnosis, and biopsy of liver is the gold standard for hepatosteatosis. However, in the viewpoints of safety, ethic and screening purpose, resting ECG and abdominal sonographic examination have acceptable reliability and are practical tools of epidem-iological survey[10,16-18,21].

Our study indicates that adult male workers with fatty liver are more likely to develop IHD compared to subjects without fatty liver. This finding is compatible to previous studies demonstrating that fatty liver, as a developer of oxidative stress plays a cardinal role in cardiac dysfunction[24,25]. Of particular significance is the fact that non-overweight subjects with fatty liver experience a significantly increased IHD risk (OR: 1.6). As Park et al[26], concluded, for non-obese men with fatty liver, systemic inflammatory response increases, and systemic inflammatory response is the integral part of the atherosclerotic process[27,28]. IHD prevention for non-overweight subjects having fatty liver should be emphasized in clinical practice.

Findings of this study show a synergistic interaction between fatty liver and overweight, this combination makes middle-aged males have significantly highest IHD risk (OR: 2.95) in the four entities (Table 4). Similar findings have been shown in studies about insulin resistance[7,10,26,29-31], these studies manifested that both overweight and fatty liver are closely correlated with insulin resistance, which aggravates the atherogenic metabolic process[32,33], accelerating the development of atherosclerosis[34] and IHD[35]. For overweight middle-aged male workers with fatty liver, a comprehensive management for IHD risk reduction is needed.

Serum sugar and lipids had insignificant effects on developing IHD in this study, these findings are similar to our previous study based on Eastern population[36]. Genetic differences[37] and differences in diet components[38] may have affected these findings.

Smoking and drinking did not show significant effects on developing IHD in this study, the partial explanation might be that binary questionnaire could provide only limited information about the dose-effect, which is important in the development of IHD, and then leads to the unsteady results[36,39].

The findings of this study demonstrate that fatty liver is an independent risk factor for IHD. Abdominal sonographic examination may not only provide limited report about the liver status, but also can provide valuable information for IHD risk assessment, especially for those who are over-weight.

The authors would like to acknowledge the personnel of the Department of Family Medicine and Internal Medicine, Shin Kong Wu Ho-Su Memorial Hospital for their full support and generous assistance.