We assigned a number to each of the 16 urban districts of Shanghai and selected two districts at random (Yangpu District and Pudong New District). Of the 11 residential districts within Yangpu and Pudong, we randomly selected the Pingliang and Shanggang residential districts, containing 30 and 26 neighborhood communities, respectively. From these, we selected eight neighborhood communities in total. Resident groups were randomly selected from each sample neighborhood community. From October 2002 to April 2003, investigations were conducted in adults aged 20 years or more in the selected resident groups at home. We excluded individuals from the study if they had a history of malignancy and other severe diseases.

This program was approved by the Research Ethics Committee of the Shanghai Health Bureau and all participants provided their written informed consent prior to their inclusion in the study. General physical examinations and laboratory assessments were performed for each study subject at a mobile examination center following an overnight fast of at least 12 h.

Interview: Selected individuals were interviewed at their homes using a self-designed questionnaire that gathered information on demographic characteristics, medical history, medications and health-related habits. Consumption of alcohol was ascertained from a series of questions including whether the respondent consumed 12 drinks (one drink is considered to contain 10 g alcohol) in the past 12 mo. If so, respondents were asked to quantify the number of days they consumed alcohol over the past 1 year and the number of drinks per day on drinking days. From these data, we calculated an average daily intake of alcohol. The questionnaire was pre-tested in the population prior to the study.

Physical examination: Body weight of the participants was measured in light clothing and without shoes to the nearest half kilogram. Their height was measured to the nearest half centimeter. Body mass index (BMI) was calculated as weight (kg) divided by height squared (m²). Waist circumference (to the nearest half centimeter) was measured at the mid-point between the lower border of the rib cage and the iliac crest, whereas hip circumference was similarly obtained at the widest point between the hip and buttock, enabling calculation of the waist-to-hip ratio. Three blood pressure readings were obtained at intervals of one min. The second and third systolic and diastolic pressure readings were averaged and used in the analyses.

Laboratory assessments: Venous blood samples were collected at 0 and 120 min following a 75 g oral glucose challenge for non-diabetics or 100 g steamed bread for diabetics. Samples were centrifuged at 2000 g for 10 min at 25°C immediately, frozen and shipped to a central laboratory of the Shanghai Center for Disease Control and Prevention, where they were stored initially at -20°C and then at -70°C. Subsequently, serum glucose was determined using a modified hexokinase method. Fasting serum total cholesterol (TC) and triglyceride concentrations were measured enzymatically by color absorptiometry based on a peroxidase-catalysed reaction. HDL-C was measured after precipitation of other lipoproteins with a polyanion/divalent cation mixture. Low-density-lipoprotein-cholesterol (LDL-C) was calculated from the measured values of TC, triglycerides and HDL-C using the following formula: LDL = (TC) - (HDL) - (triglycerides/5). LDL was not calculated if the triglyceride concentration was > 4.52 mmol/L. All these serum biochemistries were performed using a Bayer model 1650 automated bio-analyzer (Bayer Diagnostic, Basingstoke, UK).

Quality control: Field researchers were recruited from Shanghai Center for Disease Control and Prevention, and Shanghai Jiaotong University School of Medicine. Before the investigation, the researchers were given systematic training to ensure standardization of the investigation procedure. For further quality control, 5% of questionnaires and blood samples were re-examined. Kappa analysis of these samples showed a good consistency in the diagnostic test (data not shown).

Definitions: Obesity and abdominal obesity were categorized according to the new BMI criteria for Asians by the regional office for Western Pacific Region of the World Health Organization (WHO)[11]. Hypertension was defined as given in the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC7)[12]. Diagnoses of impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and type 2 diabetes were based on WHO criteria published in 1999 (WHO/NCD/NCS/99.2)[1314]. Dyslipidemia (including hypertriglyceridemia and low HDL-C) and metabolic syndrome were diagnosed on the basis of the adapted U.S. National Cholesterol Education Program’s Adult Treatment Panel III (NCEP ATP III) criteria with the exception of abdominal obesity (waist circumference 90 cm in men and 80 cm in women)[715]. We regarded participants who reported current use of antihypertensive or anti-diabetic medications or fibrates as participants with a high blood pressure or diabetes or hypertriglyceridemia, respectively.

Current alcohol consumption was defined as more than once of alcohol drink per month. The participants were then divided into current alcohol drinkers and current non drinkers, the former were further classified into light drinkers (1-9.9 g/d), moderate drinkers (10-29.9 g/d) and excessive drinkers (≥ 30 g/d) according to their average daily alcohol intake in the past 12 mo[191016].

All data were analyzed using SPSS 11.0 software (SPSS, Chicago, IL, USA). Unpaired t-test, χ² contingency test, Fisher’s exact test and trend analysis were performed whenever appropriate. Non-parametric methods were also used for abnormally distributed values. Some analyses were adjusted for age and sex. Kappa analysis was performed for blood biochemical data as a quality control. All P values provided are for two-sided tests. P < 0.05 was considered statistically significant.

We used a stratified, multistage probability cluster sampling method to obtain a representative sample from the Shanghai non-institutionalized population. The neighborhoods investigated contained 3953 residents aged 20 years or more as subjects in the present study, corresponding to approximately 2.99/10 000 of the Shanghai population according to the data collected in the Fifth China National Census in 2002 (http://www.china-un.ch/eng/ljzg/shjjtj/t85845.htm).

The study population included 1524 males and 2379 females (excluding pregnant women), giving a male to female ratio of 1:1.56. Their age ranged 20-88 years and no significant difference was noted between the ages of male and female subjects. In comparison with the sex and age obtained from the Fifth National Census of Shanghai, the study population contained a higher percentage of elderly subjects and women (P < 0.01). Therefore, some of the results were adjusted for age and sex in order to better represent the real situation in Shanghai.

Of the 3953 enrolled subjects, 448 (11.3%) had a history of current alcohol consumption, men accounted for 26.6% and women 1.8% (P < 0.001). As shown in Table 1, the prevalence of current alcohol drinking both in overall subjects and in males increased with age and reached its peak at the age of 40-49 years. However, no significant changes were found in females. After adjusted for age and sex, the prevalence of current alcoholic drinking among Shanghai adults was found to be 13.0%, which was significantly higher in males than in females (24.5% vs 1.5%, P < 0.001).

Among the 448 participants with a history of current alcohol drinking, over two-thirds (72.1%) of them were light to moderate drinkers, light to moderate female drinkers accounted for 95%. There was no difference in age among different drinking groups (Table 2). Since only 125 (27.9%) subjects were found to be excessive drinkers in the study, their average daily alcohol consumption was 58 g, and few of them were heavy or risky drinkers (alcohol consumption > 40 g/d), so we did not further distinguish heavy drinkers from excessive drinkers.

The prevalence of obesity, abdominal obesity, hypertension, hypertriglyceridemia, low serum HDL-C, diabetes mellitus and metabolic syndrome in the 3953 study subjects was 43.3%, 35.4%, 49.3%, 25.7%, 21.3%, 14.8% and 23.9%, respectively. After adjusted for age and sex, the prevalence of metabolic syndrome among adults in Shanghai was 15.3% according to the adapted NCEP-ATP III criteria[17].

The effects of current alcohol drinking on metabolic syndrome features in 3953 Shanghai adults are shown in Table 3. The blood pressure, serum concentration of triglyceride, HDL-C and FPG, prevalence of hypertension and hypertriglyceridemia were higher while the prevalence of abdominal obesity, low serum HDL-C and diabetes mellitus were lower in alcoholic drinkers than in non-alcoholic drinkers. However, the prevalence of metabolic syndrome in alcoholic drinkers only decreased mildly compared with the non-alcoholic drinkers. When adjusted for sex and age, the differences in metabolic syndrome features still existed between the two groups.

Among the 448 subjects with current alcohol consumption, the trend analysis showed that systolic blood pressure (SBP), serum HDL-C and FPG, and prevalence of hypertriglyceridemia increased progressively, while serum LDL-C, prevalence of abdominal obesity, low serum HDL-C and metabolic syndrome declined progressively with increased alcohol consumption among the three drinker groups (Table 4). When adjusted for sex and age, alcohol consumption still showed its effects on metabolic disorders among alcoholic drinkers.

Alcohol consumption is a double-edged sword to health. Light to moderate alcohol consumption is usually associated with a lower cardiovascular mortality and a reduced risk of developing type 2 diabetes mellitus. However, heavy or risky alcohol drinking is toxic to the heart and overall health, and is the third leading cause for premature death among Americans. Metabolic syndrome is associated with an increased risk of developing diabetes and cardiovascular disease, the favorable influence of alcohol consumption on selective components of metabolic syndrome has contributed to the possibility that alcohol consumption reduces the risk of metabolic syndrome in the adults of USA, Japan and South Korean. However, its putative effect on metabolic disorders has not been well evaluated in mainland China or oversea Chinese.

It was recently reported that moderate alcohol drinking is associated with a lower prevalence of metabolic syndrome. Although studies showed statistically significant interactions between alcohol consumption and metabolic syndrome, integration of variables and homogeneity in definitions is required. Since alcohol-associated health problem is also influenced by ethnicity, it is thus needed to investigate the interactions in Chinese.

One of the major findings in the present study is the relative lower prevalence of current alcohol drinking (13%) in Shanghai than in other regions of China and most foreign countries. This might be due to the different alcohol drinking culture backgrounds and the general concern about the dangers of alcohol consumption to the overall health among Shanghai people. However, metabolic syndrome is common in Shanghai as compared to Japan and South Koran, and the prevalence of metabolic syndrome among Shanghai adults is only slightly lower than that in USA, suggesting that alcohol drinking is not a major risk factor for metabolic syndrome in humans, even though current alcohol consumption is associated with a lower prevalence of metabolic syndrome irrespective of the average daily alcohol consumption in the present study. On the one hand, alcohol drinking reduces serum LDL-C concentration, risk of abdominal obesity and low HDL-C. On the other hand, alcohol consumption might increase the prevalence of hypertension, hypertriglyceridemia and hyperglycemia. These effects of alcohol consumption on metabolic disorders are consistent with the most other related or similar findings from other countries. The results of this study provide the epidemiological data on the correlation between alcohol consumption and metabolic syndrome in Chinese.

There is sufficient evidence that light to moderate alcohol consumption is associated with decreased risk of cardiovascular disease. Nevertheless, the effects of alcohol consumption on health are dependent on the consumed amount of alcohol, the pattern of drinking, and the potential for problem drinking, suggesting that alcohol should not be advised for health enhancement of individuals.

Metabolic syndrome refers to a cluster of metabolic derangements that increased the risk of developing type 2 diabetes and cardiovascular diseases associated with insulin resistance. Current alcohol drinker refers to alcohol drinking habituation regardless of the amount of alcohol consumption, and is usually defined as more than once of alcohol drinking per month over the past 12 mo. The classification of current alcohol consumption is far from consensual at present. In the present study, light alcohol drinking is defined as average alcohol consumption of less than 10 g/d, moderate alcohol drinking as average daily alcohol consumption of 10-30 g/d, and excessive alcohol drinking as average alcohol consumption of equal to or more than 30 g per day in the past 12 mo.

The authors conducted a population-based study on 3953 adults in Shanghai to evaluate the association between alcohol consumption and metabolic syndrome, and found that current alcohol consumption was associated with a lower prevalence of metabolic syndrome. Overall, the study was well designed with good quality control, and detailed data were collected from participants with a randomized multistage stratified cluster sampling method. The manuscript provides important data and is relatively well written.