In current aging societies, diabetes mellitus and neurodegenerative diseases represented by Alzheimer’s disease are highly prevalent among adults, especially the elderly all over the world. It is worth noting that a substantial body of evidence suggests diabetes contributes to accelerated neurodegenerative processes and the decline of cognition. Over the last few years, some studies have indicated neurovascular uncoupling and disrupted functional connectivity in the early stages of many neurodegenerative diseases, and the concept of the neurovascular unit (NVU) has been highlighted to understand the initiation and progression of neurodegenerative diseases recently. Considering that some components of the NVU are also demonstrated to have abnormal morphology and function under the condition of diabetes, we propose the hypothesis that diabetes may promote the onset and development of neurodegenerative diseases by impairing the integrity of the NVU, named Diabetes-NVU-Neurodegeneration Hypothesis. The existing body of literature supporting the hypothesis and elucidating the underlying mechanisms will be summarized in this review.