Cognitive decline is a debilitating feature of Alzheimer's disease (AD). The causes leading to such impairment are still poorly understood and effective treatments for AD are still unavailable. Type 2 diabetes mellitus (T2DM) has been identified as a risk factor for AD due to desensitisation of insulin receptors in the brain. Recent studies have suggested that epigenetic mechanisms may also play a pivotal role in the pathogenesis of both AD and T2DM. This article describes the correlation between AD and T2DM and provides the insights to the epigenetics of AD. Currently, more research is needed to clarify the exact role of epigenetic regulation in the course and development of AD and also in relation to insulin. Research conducted especially in the earlier stages of the disease could provide more insight into its underlying pathophysiology to help in early diagnosis and the development of more effective treatment strategies.