This cross-sectional study was based on data obtained from the Korean National Health Examination and Nutrition Survey (KNHANES) 2007–2009, conducted by the Korean Ministry of Health and Welfare. Households were selected as sampling units through a stratified, multistage, probability sampling design that was based on information such as geographic region, sex, and age group, obtained using household registries. Sampling weights, which indicates the probability of being sampled, were allocated to every subject. Thus, results based on sampling weights are representative of the entire Korean population.

During the survey period, all subjects were notified that they were randomly selected, and agreed voluntarily to participate in this nationally representative survey. Subjects were asked to complete four parts (a health interview survey, a health behavior survey, a health examination survey, and a nutrition survey) of a questionnaire. Subjects had the right to decline participation in this survey based on the National Health Enhancement Act, and submitted informed consent documents prior to participating in the study. In addition, subjects also approved the use of their blood samples for other academic purposes. A variety of information regarding the subjects was collected during the survey, including their medical history, results of physical examinations, health-related behavior, and anthropometric and biochemical data. Trained medical staff conducted physical examinations following standard methods.

Subjects answered questions regarding their lifestyle, including questions about cigarette smoking, alcohol consumption, sleep duration, physical activities, and the use of food labels. Subjects were divided into two categories: non-smokers and smokers. Drinking patterns of the subjects were assessed based on the Alcohol Use Disorders Identification Test (AUDIT) questionnaire that includes 10 points for screening subjects, and is commonly used to identify heavy drinkers.⁸⁾ Sleep duration was assessed by the following self-reported question: “On average, how many hours and minutes do you sleep per night?” To evaluate levels of physical activity, a short form taken from the International Physical Activity Questionnaire was adopted, and was translated into Korean. The survey contains questions as to whether the subjects reads food labels or not, when buying food products. Based on the answers, we classified subjects as ‘food label users’ or not.

We excluded female subjects, individuals younger than 20 years of age, those without complete anthropometric data and lifestyle behavior data, and those who did not fast overnight prior to blood sampling.

After these exclusions, 3,869 men were included in the final analysis. The institutional review board of the Korea Centers for Disease Control and Prevention approved this study.

Subjects' body weight and height were measured in light indoor clothing without shoes, to the nearest 0.1 kg and 0.1 cm, by trained medical staff. Body mass index was calculated as the ratio of weight (kg)/height (m²). The medical staff measured waist circumference at the narrowest region between the iliac crest and the 12th rib using a non-elastic tapeline. Blood pressure was measured on the subject's right arm using a mercury sphygmomanometer (Baumanometer; Baum, Copiague, NY, USA). Systolic and diastolic blood pressures were measured twice at 5-minute intervals and the average of the two measurements was recorded. After overnight fasting, blood samples were collected from the subjects through an antecubital vein puncture. Levels of glucose, triglycerides, high-density lipoprotein (HDL) cholesterol, and total cholesterol were measured using an ADVIA1650 auto-analyzer (Siemens Medical Solutions Diagnostics, Erlangen, Germany) and a Hitachi Automatic Analyzer 7600 (Hitachi Co., Tokyo, Japan). Data from a food frequency questionnaire were collected based on the 24-hour recall method. Daily energy intake was calculated using the Can-Pro ver. 2.0 software (Korean Nutrition Society, Busan, Korea), which was developed by the Korean Nutrition Society.

According to the ‘clinical practice guideline of prevention and treatment for MetS in Korea,⁹⁾ MetS is diagnosed when a subject meets three or more of the following criteria: (1) abdominal obesity, measured using the waist circumference for South Asians/Asians (waist circumference ≥90 cm in men); (2) high blood pressure; SBP ≥130 mm Hg, DBP ≥85 mm Hg, or if the subject is taking medications to treat high blood pressure; (3) high fasting blood sugar (fasting plasma glucose ≥100 mg/dL), or if the subject is taking medications to treat high blood sugar; (4) high triglyceride levels (fasting triglycerides ≥150 mg/dL), or if the subject is taking medications to treat to high triglycerides; (5) low HDL cholesterol levels (HDL cholesterol <40 mg/dL), or if the subject is taking medications to treat low HDL cholesterol.

In this study, we defined the following five factors influencing health positively: non-smokers, defined as individuals who had smoked less than 100 cigarettes in their lifetime; low-risk drinkers, defined as individuals with an AUDIT score between 0–14; adequate sleepers, defined as individuals who slept for 6–8 hours a day on average; regular exercisers, defined as individuals who engaged in moderate to vigorous-intensity physical activity three or more days per week; and food label users, defined as individuals who usually read food labels when buying food products.

Finally, we categorized the subjects into four groups according to the number of positive practices that they engaged in on a daily basis: group I, 0–1 positive practice; group II, 2 positive practices; group III, 3 positive practices; group IV, 4–5 positive practices.

For the subjects in the 2007–2009 KNHANES to represent the entire Korean population, we applied sampling weights to take the complex sampling method into account. Mean values of continuous variables such as age, waist circumference, blood pressure, daily energy intake, and other laboratory data were compared among the four groups using general linear models. Chi-square tests were used to compare inter-group differences in categorical variables including the five positive factors (non-smoker, low-risk drinker, adequate sleeper, regular exerciser, and food label user), education level of the subject, and the prevalence of MetS.

All data are presented as mean±standard error. Multiple logistic regression analyses were performed to calculate odds ratios (ORs) for MetS and each of its diagnostic components according to the number of factors influencing health positively, after adjusting for confounding variables such as age, socioeconomic status (education status, household income), and daily energy intake. All analyses were conducted using SAS statistical software ver. 9.1 (SAS Institute Inc., Cary, NC, USA). All statistical tests were two-sided and statistical significance was set to a P-value of <0.05.

Cigarette smoking is the most important preventable cause of death and illness. Prohibiting cigarette smoking or motivating its cessation promotes public health. A number of studies have revealed that cigarette smoking is related to a higher risk of developing MetS in a positive, dose-dependent manner.¹⁰⁾ While cigarette smoking, including second-hand smoking, impairs insulin sensitivity and elevates triglyceride levels and blood pressure,¹¹⁾ cessation of smoking improves insulin sensitivity and lipoprotein profiles, despite a slight gain in weight.¹²⁾ The effects of cigarette smoking on glucose and lipid metabolism may contribute to the stimulation of cortisol circulation and release of the growth hormone, which have insulin-antagonistic effects.¹³⁾ Even though cessation of cigarette smoking might cause weight gain,¹⁴⁾ the beneficial effects of cessation outweigh its adverse effects.

Alcohol consumption is very popular in Korea; 81.6% of men and 52.4% of women in Korea have lifestyles that involve alcohol consumption. The amount of alcohol consumed daily per capita is 30.1 g for men and 6.6 g for women. Numerous epidemiological studies have reported a J- or U-shaped association between alcohol-drinking and cardiovascular morbidities/mortality. Heavy alcohol intake can cause metabolic dysfunction and is associated with a higher risk of cardiovascular events, while light to moderate alcohol intake can lower cardiovascular events and elevate HDL cholesterol levels.^15,16) However, conflicting results have been reported regarding the relationship between alcohol consumption and MetS.¹⁷⁾ In addition to the total amount of alcohol intake, unhealthy drinking patterns are considered an important risk factor for MetS in men.¹⁸⁾ We categorized subjects as high-risk drinkers or others according to the AUDIT score. Because the AUDIT questionnaire consists of 10 screening questions including frequency of drinking, quantity of drinks consumed, adverse events after drinking, among others, it not only assesses the amount of alcohol consumed, but also identifies heavy drinkers.¹⁹⁾ Drinking alcohol stimulates the appetite through reduction of glycemic levels, and causes obesity-related disorders including dyslipidemia and diabetes mellitus.²⁰⁾ Chrysohoou et al.²¹⁾ reported that chronic alcohol consumption is associated with glycemic levels, triglyceride levels, and arterial blood pressure in a J-shaped manner. Our results are therefore consistent with those reported by previous studies. High-risk drinking patterns may contribute to a higher prevalence of MetS.

It is well-known that increased physical activity maintains and promotes health and reduces mortality, regardless of a reduction in body weight.²²⁾ Several studies have confirmed that being physically active is associated with a lower risk of developing MetS, in a dose-responsive manner.²³⁾ Interventions to increase physical activity in individuals with MetS reduced the prevalence of MetS and improved its diagnostic components.^24,25) A meta-analysis of seven randomized-controlled trials by Pattyn et al.²⁵⁾ demonstrated that waist circumference and blood pressure were significantly reduced in healthy adults with MetS after endurance exercise, while HDL cholesterol levels were increased. Aerobic exercise training is a useful tool to manage MetS, as well as to decrease abdominal obesity, glucose intolerance, blood pressure, and dyslipidemia.²⁴⁾

Although several epidemiological studies have suggested that the duration of sleep plays an important role in the development and progression of MetS, other studies have not observed this association. Some studies report a U-shaped relationship between duration of sleep and the development of MetS. More recently, a positive relationship between a short duration of sleep and the risk of developing MetS was reported, based on findings from a meta-analysis.²⁶⁾ The mechanism linking duration of sleep and the development of MetS is not clear. However, Spiegel et al.²⁷⁾ suggested that sleep deprivation disturbs energy balance and glucose metabolism. In addition, short duration of sleep causes hormonal dysregulation, such as a decrease in leptin levels and increase in ghrelin levels, which result in overeating and weight gain.²⁸⁾ Evidence demonstrating a relationship between long duration of sleep and the development of MetS is mixed. Individuals that sleep for a long time may have less waking hours to incorporate physical activities, resulting in a relatively sedentary lifestyle. For the above-mentioned reasons, sleeping too much or too little are both possible risk factors for the development of MetS.

Disclosure of nutritional information on food products is expected to decrease calorie consumption and fat intake, and have a positive effect on public health;²⁹⁾ however, the effectiveness of food labeling is still unclear.³⁰⁾ Health authorities in various countries have drafted legislatures to ensure that nutrition information is made available on food packaging to promote public health. Kang et al.³¹⁾ reported that food label users drawn from the Korean population had a lower risk of developing MetS. They showed that food label users consumed larger amounts of anti-oxidants such as vitamin A and C. These results appear to be consistent with conclusions from other studies, that the development of MetS is positively associated with oxidative stress and is inversely related to blood anti-oxidant levels.³²⁾

Although the above-mentioned relationships between individual positive health factors and MetS are frequently found, the combined effect of positive factors influencing health, and the underlying mechanisms of these interactions are less well studied. But these positive lifestyle factors are likely to interact with one another and aggregate in clusters.³³⁾ Combinations of health behaviors may have synergistic effects on the risk of developing disease.^34,35,36) In this study, we suggest that lifestyle factors should be considered together, rather than in isolation when researching MetS.

There are several limitations to this study. First, it was impossible to establish causality between healthy lifestyle practices and the development of MetS, because this study had a cross-sectional design. However, several prospective studies have indicated that each of the positive factors we examined protects against the development and progression of MetS.³⁾ Furthermore, Banda et al.³⁷⁾ reported that a combination of healthy lifestyle factors reduced new-onset hypertension in men. Second, we could not fully exclude the possibility of mis-classification, because this study was based on a self-reported questionnaire. Individuals with unhealthy lifestyles may have been miscategorized into a healthy lifestyle group because they did not report socially undesirable lifestyle habits such as cigarette smoking or high-risk drinking. Third, we assessed health influencing factors using qualitative rather than quantitative methods. Future studies should assess the dose-response association between health influencing factors and the development of MetS using quantitative methods. Further, each beneficial or health influencing factor was given equal weight in this study. The next study should consider the effect of size for each component.

Despite these potential limitations, this study has several strengths. We conducted all statistical analyses after applying sampling weights to nationwide data that were collected through a multistage probability-based complex sampling approach. Thus, our data are representative of the general Korean male population aged 20 years or older. We performed additional analyses to determine the relationship between positive factors and each component of MetS, after adjusting for age, daily energy intake, socioeconomic status, and other components of MetS. A positive impact of modifying lifestyle practices were seen on abdominal circumference, blood pressure, serum glucose, and triglyceride except HDL cholesterol level.

In conclusion, we found that Korean men who incorporated a greater number of healthy practices in their daily lives were at lower risk of developing MetS than men who incorporated fewer healthy practices, after adjusting for possible confounding factors such as age, education level, daily energy intake, and household income. These findings indicate that individuals should be encouraged to incorporate positive habits into their daily lives to promote their health and prevent the development of MetS, especially in those individuals with abdominal obesity, glucose intolerance, or hypertriglyceridemia. In addition, healthcare provider interventions may be more effective at preventing and treating MetS, if the fact that these factors cluster and interact with one another is taken into consideration.