Aside from the COVID-19 pandemic, the obesity and diabetes pandemics have threatened global health. Patients with diabetes are more likely to experience serious complications from COVID-19; thus, preventing obesity-associated diabetes is of paramount important. Furthermore, the development of a method to prevent diabetes and elucidation of its pathology is a currently urgent issue. We previously reported that thiamine plays a key role in suppressing abnormal glycolipid metabolism in Otsuka Long-Evans Tokushima fatty (OLETF) rats, an animal model of obesity-associated diabetes. However, whether thiamine affects only OLETF rats or other animal models including a type 2 diabetes model with a different pathology requires elucidation. In this study, leptin-receptor deficiency mice were used as a model of type 2 diabetes with a different pathology to evaluate the efficacy of thiamine. The mice had free access to water containing 0.2% thiamine for 9 weeks, and the results showed that food and water consumption decreased in db/db-homo mice. Urine output, body weight gains and blood glucose levels decreased in mice that received thiamine. There were 5 mice and 1 mouse with a fasting glucose level of ≥ 300 mg/dL in the db/db-homo control group (n = 10) and db/db-homo thiamine group (n = 10), respectively, suggesting that thiamine intake may suppress an increase in blood glucose levels. The results of the present study suggest that demand for thiamine may exceed the normal range in in vivo mouse models of diabetes and continuous thiamine intake affects diabetes onset and progression.