In recent years, medical research has sparked hope that up to a third of dementia cases could be prevented. This optimism is driven by a shift in the understanding of dementia and, in particular, Alzheimer's Disease (AD)-from being a rapid-onset brain disease in later life to a condition strongly linked to lifestyle factors, progressing slowly and gradually through asymptomatic, pre-symptomatic, and symptomatic stages with varying degrees of severity. Accompanying this evolving perception, the use of mobile healthcare applications (mHealth apps) based on dementia prevention research has been on the rise. Health policymakers and companies increasingly advocate for these apps. However, concerns remain about the medical quality of such mHealth apps for dementia prevention. Bioethical research has highlighted significant challenges associated with their use. This paper critically examines dementia prevention strategies through the lenses of mHealth technologies. Exploring four mHealth apps for dementia prevention as case studies, we identify and analyze unsolved ethical issues related to primary, secondary, and tertiary prevention. Hereby we offer a new perspective on familiar ethical dilemmas in dementia prevention, and emphasize the need to examine potentially intensified challenges in the context of digital health in the future in more depth.