Associations between normal weight central obesity and cardiovascular disease risk factors in Japanese middle-aged adults: a cross-sectional study

BACKGROUND: Several studies have shown that normal weight central obesity (NWCO) is associated with cardiovascular disease (CVD) risk factors. However, studies conducted in the Japanese population have been very limited. Thus, the relationships between normal weight central obesity, classified using body mass index (BMI), the waist-to-height ratio (WHtR), and CVD risk factors in middle-aged Japanese adults were investigated. METHODS: The participants were Japanese adults aged 40–64 years who had undergone periodic health examinations in Japan during the period from April 2013 to March 2014. The participants were categorized into the following four groups: normal weight (BMI 18.5–24.9 kg/m(2)) and no central obesity (WHtR < 0.5) (NW); normal weight and central obesity (WHtR ≥ 0.5) (NWCO); obesity (BMI ≥ 25 kg/m(2)) and no central obesity (OB); and obesity and central obesity (OBCO). Hypertension was defined as systolic blood pressure ≥ 140 mmHg, diastolic blood pressure ≥ 90 mmHg, or taking medication for hypertension. Dyslipidemia was defined as LDL-C ≥ 140 mg/dl, HDL-C < 40 mg/dl, triglyceride ≥ 150 mg/dl, or taking medication for dyslipidemia. Diabetes was defined as fasting plasma glucose ≥ 126 mg/dl, random plasma glucose ≥ 200 mg/dl, HbA1c ≥ 6.5%, or receiving medical treatment for diabetes mellitus. A logistic regression model was used to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) for hypertension, dyslipidemia, and diabetes. RESULTS: A total of 117,163 participants (82,487 men and 34,676 women) were analyzed. The prevalence of NWCO was 15.6% in men and 30.2% in women. With reference to NW, the ORs for hypertension (adjusted OR 1.22, 95% CI 1.17–1.27 in men, 1.23, 1.16–1.31 in women), dyslipidemia (1.81, 1.74–1.89 in men, 1.60, 1.52–1.69 in women), and diabetes (1.35, 1.25–1.46 in men, 1.60, 1.35–1.90 in women) were significantly higher in NWCO. CONCLUSIONS: Normal weight with central obesity was associated with CVD risk factors, such as hypertension, dyslipidemia, and diabetes, compared with normal weight without central obesity, regardless of sex. It is important to focus on normal weight with central obesity for the prevention of CVD in Japanese middle-aged adults.