People diagnosed with diabetes before the age of 65 are more than twice as likely to develop dementia in old age, a new study has found. The discovery is part of an ongoing study of Swedish twins who researchers followed from 1998 to 2001. Of the 13,693 participants, 467 were diagnosed with dementia, including 292 people who developed Alzheimer's. Researchers say their discovery highlights the need of adults to maintain good health throughout middle age in order to help prevent dementia later.