The prevalence of psychological disorders—abnormal changes in personality and behavior that may be caused or triggered by a genetic predisposition, environmental stress, and/or systemic diseases—in old age is difficult to determine, although estimates range from 5 to 45 percent of the older population. Depression, the most common mental disorder in late life, is difficult to diagnose. Both older adults and some health care providers may deny symptoms and accept "feeling blue" as normal aging, while others attribute it to other chronic illnesses. Reactive or minor depression that is secondary to major life changes is found most frequently in older persons, and responds well to environmental and psychosocial interventions. Antidepressant medications combined with short-term problem-solving and cognitive-behavioral therapies are effective treatments for major depression. Life review and reminiscence therapy are also often used. Depression is a risk factor for suicide in older people, particularly for white men over age 85 who have faced role losses.
Some studies have identified rates of anxiety disorders as high as or higher than depression, and both conditions are often co-occurring. Paranoia and schizophrenia are far less common, and typically develop earlier in life and are aggravated by chronic diseases.
Dementia, due to both reversible and irreversible conditions, results in major impairments of cognitive function, especially recall of recent events, comprehension, learning, attention, and orientation to time, place, and person. Thorough tests are needed to distinguish reversible dementias that can be treated from the irreversible dementias such as Alzheimer's disease, which can only be managed. The Nun Study and research on the cognitive benefits of exercise provide useful insights into early life experiences and activities that may prevent or delay the onset of dementia. The biological basis of Alzheimer's disease is receiving more research attention. Future treatments may involve medications that replace or prevent the loss of brain chemicals, as well as vaccines and even gene therapy. People with AD may show symptoms of the disease three to five years before diagnosis. This period, when changes are present but the full-blown disease is absent, is called "mild cognitive impairment" or MCI. It is important to understand that not everyone with MCI goes on to develop AD. In fact, as many as 40-50% may never develop the disease. (See the FCA fact sheet Mild Cognitive Impairment (MCI).) Early problems are often seen as normal changes due to aging, and only in retrospect do caregivers see that symptoms have been occurring for several years. Although on average, individuals survive four to eight years once diagnosed, living for 20 years is not all that unusual. For ease in understanding the changes that occur as the disease progresses, AD is generally divided into three stages: early, middle, and late. However, the development of symptoms in an individual will differ from person to person, as will the progression of symptoms.