The World Health Organization (WHO) reports that in 2019 around 264 million people were suffering from depression globally. Mental disorders continue to grow with significant impacts on the physical, social and economic well-being of people across the globe.

Several studies conducted in the past have confirmed that psychiatric disorders such as depression and anxiety can be a risk factor for Alzheimer's disease. However, the effects of other psychiatric disorders on Alzheimer’s disease have not been investigated enough. Recent research conducted by the scientists of the University of California San Francisco Memory and Aging Center, California, found that other psychiatric disorders may also be responsible for earlier onset of Alzheimer's disease.

What is Alzheimer’s Disease?

Alzheimer's disease (AD) is a progressive brain disorder that slowly shrinks the brain and destroys brain cells. This destruction is irreversible and causes a continuous decline in the thinking, remembering, behavioural and social skills of the affected person. It is usually seen in people over the age of 65 years but can occur in much younger people. The cause of AD is not understood completely but is believed to be a result of an abnormal build-up of proteins (amyloid) in and around brain cells.

The new study

A new study presented at the American Academy of Neurology (AAN) 2021 Annual Meeting in April examined 1500 people diagnosed with Alzheimer’s disease. These patients were screened for a history of five psychiatric disorders - depression, anxiety, bipolar disorder, post-traumatic stress disorder, and schizophrenia.

In this study, scientists further analysed the time when these patients first developed the symptoms of depression before the onset of Alzheimer’s disease; within 2 years, between 2 to 10 years, or more than 10 years.

The scientists also looked for other well-established risk factors of Alzheimer's disease, such as high blood pressure, high cholesterol, diabetes, an autoimmune disease, or a history of seizures.

Results of the study

The results of the study showed that:

• Out of all the patients, 43% suffered from depression, 32% had anxiety, 1.2% of the participants had bipolar disorder, 1% had post-traumatic stress disorder, and 0.4% had schizophrenia.
• Female patients were more likely to get diagnosed with depression and anxiety as compared to male patients. This signified that depression and anxiety could be an early sign of Alzheimer’s disease in women.
• Female patients developed the symptoms of AD at a younger age as compared to their male counterparts.
• The age of onset of Alzheimer’s disease in people diagnosed with depression is about 2 years earlier, while for patients with anxiety, the age of onset is 3 years earlier compared to those without any psychiatric disorders.
• Participants with only one psychiatric disorder developed AD symptoms 1.5 years before the ones with no psychiatric disorders.
• Participants with two psychiatric conditions exhibited symptoms of AD 3.3 years earlier than those with no mental health issues.
• Participants with three or more psychiatric disorders started developing AD symptoms 7.3 years before the ones with no mental disorders.
• Participants diagnosed with depression were more likely to present with an autoimmune disease, while those diagnosed with anxiety showed a history of seizures.

Conclusion

With this study, scientists concluded that people diagnosed with more than one psychiatric disorder are at increased risk of developing Alzheimer’s disease at an early age. Scientists believe that inflammation in the nervous system (neuroinflammation) could be one of the reasons for depression and earlier onset AD.

However, the study did not consider the potential side effects of the medications used to treat depression and anxiety. Further research needs to be carried out to determine if the treatment and management of psychiatric disorders such as depression and anxiety can help prevent or delay the onset of Alzheimer’s disease and dementia in high-risk groups. It is not necessary that people with depression and anxiety would develop Alzheimer's disease, but such individuals could work with mental health experts to develop strategies to promote long-term brain health.