This was a cross-sectional study that screened 2,885 Japanese adults who participated in a voluntary health checkup conducted at Juntendo University Hospital from January 2017 to December 2018, in Tokyo, Japan. A total of 978 subjects were excluded due to missing data, and 1 subject was excluded due to a duplicate case. Ultimately, 1,907 participants were included in the present study (men, 1,050; women, 857).
Height, weight, body mass index (BMI), and WC were measured with participants in the standing position. BMI was calculated by dividing body weight (kg) by height squared (m2). Mean systolic blood pressure (SBP) and diastolic blood pressure (DBP) were calculated from the means of two upper-arm blood pressure measurements taken from participants who had been seated for at least 5 minutes. Serum levels of total cholesterol (mg/dl; TC), high-density-lipoprotein cholesterol (mg/dl; HDL-C), low-density-lipoprotein cholesterol (mg/dl; LDL-C), and triglycerides (mg/dl; TGs) were also measured. LDL-C was estimated using the Friedewald equation [(TC) – (HDL-C) – (TG/5)] . Hemoglobin A1c (HbA1c) levels were determined by high-performance liquid chromatography using an automated analyzer. Serum uric acid (mg/dL) and high-sensitivity C-reactive protein (mg/dl) were also measured.
Participants were asked to complete a self-administered questionnaire that addressed healthy lifestyle characteristics based on Breslow’s seven health practices . These characteristics can be used to assess lifestyle health, and strong associations have been found between healthy lifestyle practices and successful blood pressure control among patients with hypertension . Healthy lifestyle items in the questionnaire included non-daily alcohol consumption, non-smoker status, exercise frequency of two or more times per week, BMI of 18.5-24.9 kg/m2, adequate sleep duration, daily breakfast consumption, and no snacking between meals [12-13].
From the self-administered questionnaire, we also collected information on present medical history of comorbidities, such as hypertension, DM, dyslipidemia, hyperuricemia, cardiovascular disease, and cerebrovascular disease. If participants answered as having these comorbidities, we registered the participants with a medical history of these comorbidities (present).
CT measurement of abdominal adipose tissue
Abdominal fat area, including VFA and SFA, was measured from CT scans taken at the level of the umbilicus while in the supine position and during late expiration according to Japanese guidelines for obesity treatment . An Aquilion ONE/GENESIS Edition CT scanner (Canon Medical Systems Corp., Tokyo, Japan) was used to obtain CT scans. We manually traced the inner aspect of the whole trunk, muscular layer, and the abdominal wall. In the computerized method using commercial software designed for quantification of VFA and SFA (Canon Medical Systems Corp.), fat was defined as any tissue with a threshold of −150 to −70 Hounsfield units. Abdominal VFA was defined as the fat area enclosed by the inner aspect of the abdominal wall, and SFA was defined as the fat area enclosed by the outer aspect of the abdominal wall [15,16]. The method is widely used and a previous study indicated that CT and magnetic-resonance imaging (MRI) may yield different absolute values of fat areas (especially visceral fat) but that the ranking of individuals on the basis of their fat areas will be similar by both methods [17,18].
Definition of lifestyle-related disorders
Lifestyle-related disorders were defined according to the following criteria: 1) DM, high fasting plasma glucose (≥126 mg/dl) or HbA1c (≥6.5%) or taking antidiabetes medications; 2) hypertension, increased blood pressure (SBP ≥140 mmHg or DBP ≥90 mmHg) or taking antihypertensive medications; 3) dyslipidemia, increased TG level (≥150 mg/dL) or LDL-C level (≥140 mg/dL) or reduced HDL-C level (<40 mg/dL) or taking dyslipidemia medications .
Results are presented as mean ± standard deviation (SD) for continuous variables or prevalence (%) for categorical variables by sex. VFA and SFA quartiles were defined by sex [men; VFA (cm2): Q1 < 65, 65 ≤ Q2 < 95, 95 ≤ Q3 < 125, 125 ≤ Q4: SFA(cm2): Q1 < 85, 85 ≤ Q2 < 115, 115 ≤ Q3 < 155, 155 ≤ Q4], [women; VFA (cm2): Q1 < 30, 30 ≤ Q2 < 60, 60 ≤ Q3 < 85, 85 ≤ Q4: SFA(cm2): Q1 < 90, 85 ≤ Q2 < 135, 135 ≤ Q3 < 190, 190 ≤ Q4]. Associations between VFA or SFA quartiles and DM were identified using adjusted odds ratios (AORs) and 95% confidence intervals (CIs) with multivariable logistic regression analysis adjusted for age (years), dyslipidemia (yes), hypertension (yes), hyperuricemia (yes), alcohol consumption (non-daily drinker), and smoking (non-smoker).
Receiver operating characteristic (ROC) curve analysis was used to assess appropriate cut-off values of VFA and SFA, and we estimated the area under the curve (AUC) and measured the sensitivity and specificity for DM in both sexes. All statistical analyses were performed using the Statistical Package for Social Sciences, version 22 (SPSS Inc., Chicago, IL, USA).
The research protocol was reviewed and approved by the Ethics Committee of the Juntendo University Hospital (no. 18-297), and written informed consent was obtained from all participants.