People who experienced high anxiety any time in their lives had a 48% higher risk of developing dementia compared with those who had not, according to a new study.

OT_News-01The study, led by researchers with the University of Southern California in Los Angeles, was based on an examination of 28 years of data from the Swedish Adoption Twin Study of Aging, overseen by the Karolinska Institutet of Sweden. The study sample involved 1,082 participants — fraternal and identical twins — who completed in-person tests every three years, answered several questionnaires and were screened for dementia throughout the study.

Many past studies have explored the link between dementia and psychological variables such as depression and neuroticism. However, this study showed the anxiety-dementia link was independent of the role of depression as a risk factor, according to a news release.

“Anxiety, especially in older adults, has been relatively understudied compared to depression,” lead author Andrew Petkus, PhD, postdoctoral scholar and research associate of psychology in the USC Dornsife College of Letters, Arts and Sciences, said in the release. “Depression seems more evident in adulthood, but it’s usually episodic. Anxiety, though, tends to be a chronic lifelong problem, and that’s why people tend to write off anxiety as part of someone’s personality.”

A final draft of the study was published Nov. 5 on the website of Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association.

The researchers noted the subjects had self-reported various levels of anxiety, which may or may not meet the clinical diagnostic threshold of a psychiatric anxiety disorder. Even so, their findings showed the twin who developed dementia had a history of higher levels of anxiety compared with the twin who did not develop dementia.

‘Frantic, frazzled people’

The subjects with anxiety who later developed dementia “are people that experience more than usual symptoms of anxiety,” study co-author Margaret Gatz, PhD, said in the release. Gatz, a psychology professor in the USC Dornsife College of Letters, Arts and Sciences, holds joint appointments in the USC Davis School of Gerontology and the Keck School of Medicine of USC. She also is a foreign adjunct professor for the Karolinska Insitutet.

“They are people who you would say operate at a ‘high level of anxiety,’” Gatz said in the release, adding they are fidgety. “They are frantic, frazzled people.”

To determine whether anxiety levels correlated to dementia risk, researchers compared those who reported high anxiety with those who reported lower anxiety levels.

“Those in the high anxiety group were about 1.5 times more likely to develop dementia,” Petkus said in the release.

Possible explanation

Petkus said people who have high levels of anxiety tend to have higher levels of stress hormones, including cortisol. Evidence has shown chronically high levels of cortisol damage parts of the brain such as the hippocampus, which stores memory, and the frontal cortex, which is responsible for high-level thinking.

The researchers also found the anxiety-dementia relationship was stronger among fraternal twins than among identical twins. According to the researchers, this finding indicates there might be genetic factors shared by anxiety and dementia that account for the anxiety-dementia risk.

The USC team also hopes to determine whether individuals who have been treated for anxiety earlier in their lives show lower risk of dementia compared with those whose anxiety was not treated.

The Swedish Adoption Twin Study of Aging is funded by grants by the MacArthur Foundation Research Network on Successful Aging, the Swedish Council for Working Life and Social Research and the Swedish Research Council. Petkus received support from the Ruth L. Kirschstein National Service Award fellowship from the National Institute on Aging.

Study abstract: http://www.alzheimersanddementia.com/article/S1552-5260(15)02914-3/abstract