A study that followed 800 Swedish middle-aged women from 1968 to 2005 has found that high levels of stress in middle age increased Alzheimer’s risk by 21% and risk of any dementia by 15%.
Of the 800 women, 425 died during the course of the study while 153 (19%) developed dementia (of whom 104 developed Alzheimer’s), at an average age of 78. The number of stressors and long-standing distress were independently associated with Alzheimer’s.
The finding doesn’t tell us whether stress is contributing to the development of dementia, or whether it is simply an indicator of another underlying risk factor.
The open access paper is available at http://bmjopen.bmj.com/content/3/9/e003142.abstract.
 . Common psychosocial stressors in middle-aged women related to longstanding distress and increased risk of Alzheimer's disease: a 38-year longitudinal population study. BMJ Open [Internet]. 2013 ;3(9). Available from: http://bmjopen.bmj.com/content/3/9/e003142