(1) Background: As no study has evaluated the risk factors contributing to the development of type 2 diabetes according to body weight mass (BMI) categories in a large cohort and over a long period in a Japanese population, we aimed to assess them in 46,001 Japanese individuals; (2) Methods: This long-term retrospective cohort study included individuals who participated in a medical health checkup program at Panasonic Corporation from 2008 to 2018. In total, 3,208 participants developed type 2 diabetes. The BMI at 2008 were divided into 3 groups: BMI < 22 kg/m2, 22 ≤ BMI < 25 kg/m2, and BMI ≥ 25 kg/m2 to evaluate the risk factors for type 2 diabetes; (3) Results: Cox regression analyses revealed that the significant risk factors were age, BMI, systolic blood pressure, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, fasting plasma glucose, current smoking status, and alcohol consumption in populations with BMI ≥ 25.0 kg/m2. The risk factors in the population with 22 ≤ BMI < 25 kg/m2 were identical to that of BMI ≥ 25.0 kg/m2 excluding systolic blood pressure, low-density lipoprotein cholesterol, and skipping breakfast. However, in the population with BMI < 22.0 kg/m2, no association was found as to BMI, SBP, LDL cholesterol level, and triglycerides; (4) Conclusions: The risk factors for developing diabetes were quite different between the population with BMI < 22 kg/m2 and the population with 22 ≤ BMI < 25 kg/m2 or BMI ≥ 25 kg/m2 in a Japanese population.

It has been reported that oral health is associated with some co-morbid conditions, including cardiovascular disease, in people with type 2 diabetes mellitus. The present study investigated the association between the frequency of toothbrushing and lifestyle in people with type 2 diabetes mellitus. This cross-sectional study included 624 outpatients at the Kyoto Prefectural University of Medicine in Kyoto, Japan from January 2014 to January 2016. Lifestyle was evaluated using a self-administered questionnaire. The average age and hemoglobin A1c level were 67.6 ± 10.9 years and 7.2 ± 1.1%, respectively. The number of patients who brushed their teeth twice or more a day was 189 (50.3%) in men and 198 (79.8%) in women. Among men, the proportion of patients living alone was lower in those who brushed their teeth twice or more a day than those who brushed their teeth never/rarely or once a day. The logistic regression analysis, after adjusting for confounding factors, revealed that living alone (odds ratio 2.88; 95% confidence interval 1.53-5.66) was associated with the increased odds of the low frequency of toothbrushing (never/ rarely or once a day) in men, but not in women. In conclusion, the results of our study suggest that living alone was associated with the low frequency of toothbrushing in people with type 2 diabetes mellitus, particularly in men.