Subjective cognitive impairment (SCI), marked by situations such as when a person recognizes they can't remember a name like they used to or where they recently placed important objects the way they used to, is experienced by between one-quarter and one-half of the population over the age of 65. A seven-year study involving 213 adults (mean age 67) has found that healthy older adults reporting SCI are dramatically more likely to progress to MCI or dementia than those free of SCI (54% vs 15%). Moreover, those who had SCI declined significantly faster.
Reisberg, B. et al. 2010. Outcome over seven years of healthy adults with and without subjective cognitive impairment. Alzheimer's & Dementia, 6 (1), 11-24.