Why Do Mental Illnesses—From Depression to Schizophrenia—Raise the Risk of Dementia?

The risk of dementia increases every five years after age 65. There are a lot of things that affect the odds for an individual. Smoking, social isolation, and impaired hearing and vision are some of the risk factors that contribute to genetic vulnerability. Depression and Schizophrenia have been linked to dementia. Depression can be a sign of cognitive decline. An analysis of data from New Zealand gave the most convincing evidence to date that mental illness and dementia are related. The study raises questions about the reasons for the increased risk and what can be done to decrease it.

The study looked at the health records of 1.7 million people who were born between 1928 and 1967. People with a diagnosed mental disorder were four times more likely to develop dementia than people without such a diagnosis. It was six times the rate for people with a psychotic disorder. People with a mental illness were more likely to develop dementia than those without it.

Research on dementia points to several possible explanations for the increased risk. According to the study, there may be shared genetic risk factors. There are some genetic markers associated with Alzheimer's disease and other mental illnesses. The authors don't think long-term use of psychiatric medication is a major contributor to dementia.

Chronic stress associated with having a mental illness may be a more significant risk factor. Chronic stress has been linked to a loss of neural connections in the hippocampus, the brain's memory center, which can lead to Alzheimer's. Steven Arnold is a Harvard University neurologist and dementia researcher. If you have fewer connections to begin with because of stress, then you can't afford to lose as many as possible before it starts to show up as dementia. The brainpower of people with mental illnesses may not be as strong as it could be.

It's possible that vulnerability in this population is related to their finding it more difficult to lead a healthy life. They might have trouble staying socially connected, which increases the risk for dementia. Smoking and less education are risk factors for people with certain mental illnesses.

The risk for dementia could be mitigated by a moreholistic approach to treatment of mental illness. Some researchers think so. Four in 10 cases of dementia could be prevented or delayed if society did a better job of addressing 12 risk factors, according to a British commission. For the past 30 years in high-income countries, the rate of dementia has fallen due to progress on some of these factors. Kenneth Langa of the University of Michigan is an associate director of the Health and Retirement Study, one of the major efforts tracking these trends.

Langa and other researchers say that efforts to prevent dementia should begin in childhood with strong investments in education. Depression and other mental illnesses are more common in the teen and early adult years. We don't live in a world where mental illness is treated with the same level of care as physical illnesses. It is hard to imagine a better investment given the high costs to society and the personal tolls of mental illness and dementia.