New Data Assign Inflammation Crucial Role in Mental Decline
Abstract
Chronically heightened inflammation, often due to chronic physical and mental stress, has long been implicated in a variety of age-related physiological changes such as cardiovascular and immune disorders. Research has shown that the brain is also harmed by the inflammatory process, drawing a picture of mind and body that are inseparable.
A group of papers published in the September American Journal of Geriatric Psychiatry has added to the mounting evidence that inflammation is an important contributor to various mental declines associated with aging and may be a good target for interventions to prevent these declines.
Poor Sleepers Overreact to Acute Stress
One of these studies examined the link between sleep and inflammatory response to acute stress, since sleep disturbances become more common with older age. Kathi Heffner, Ph.D., of the Rochester Center for Mind-Body Research at the University of Rochester Medical Center in New York and colleagues demonstrated that inflammatory response to acute stress, measured by rise in interleukin-6 (IL-6) concentration in blood, was exaggerated in poor sleepers compared with good sleepers.
IL-6 is one of many cytokines that send signals throughout the body to promote inflammation. Other cytokines, such as IL-4 and IL-10, are anti-inflammatory signals to counterbalance the inflammation process. This balance is often tipped toward inflammation as people age.
This study tested healthy adults aged 50 to 87; the study population included 45 postmenopausal women and 38 men. None had depression or anxiety disorders. About 25 percent of these volunteers were poor sleepers, but their baseline IL-6 levels were similar to those of good sleepers.
Acute stress was induced by giving the subjects a series of neuropsychological tests. The study volunteers had blood samples drawn before and after the tests.
The authors suggested that improving sleep in older adults may prevent inflammatory response to acute stress and subsequently stress-related chronic inflammation.
Link to Memory Problems Found
In another study, memory performance was negatively correlated with circulating IL-6 levels.
Researchers, led by Virginia Elderkin-Thompson, Ph.D., of the UCLA Semel Institute for Neuroscience and Human Behavior at the University of California, Los Angeles, gave a series of cognitive function tests to 87 volunteers aged 60 or older. These included 42 participants who qualified for a diagnosis of depression and who were compared with 45 nondepressed participants. Baseline IL-6 levels did not significantly differ between the two groups.
Higher IL-6 levels were significantly associated with worse performance on memory tests in both depressed and non-depressed subjects, but were not associated with performance on executive function or attention and processing tests. This link between IL-6 and memory was more prominent in women, suggesting that women may be more sensitive to the neurological effects of inflammation.
C-reactive protein, another marker for inflammation, was not associated with any of the cognitive functions.
The authors also found an association between depression and worse memory performance that was independent of IL-6 level and factors such as age and literacy. Although not clearly detected in this study, a connection between pro-inflammatory cytokines and depression has been indicated in other research studies, the authors pointed out.
Exercise Can Stem Inflammatory Tide
A six-month study, also conducted at UCLA, suggests that behavioral interventions such as exercise and meditation can prevent the rise of inflammation with age. The study also confirmed a significant correlation between decrease in depressive symptoms and decreased IL-6 levels.
A UCLA study suggests that behavioral interventions such as Tai Chi Chih and meditation can prevent the rise of inflammation with age.
In this case, the exercise is Tai Chi Chih, a form of exercise modified from Tai Chi with elements of aerobic activity, relaxation, and meditation. The 83 healthy volunteers aged 59 to 86 were randomly assigned to two groups: one group was taught Tai Chi Chih and practiced it at home, the other group was given health education.
The instructions for either Tai Chi Chih or health education about aging were given three times a week for 16 weeks, with each session lasting 40 minutes. In the Tai Chi Chih group, the mean IL-6 level decreased from 2.25 pg/mL at baseline to 2.04 at week 25, nine weeks after the end of instructions. In the health-education group, the mean IL-6 level increased from 1.87 pg/mL at baseline to 2.64 pg/mL at week 25. The between-group comparison in IL-6 level change over time did not reach statistical significance (p=0.07), but the authors considered the findings potentially useful and suggested that a larger sample size could lead to a clearer result. 
Abstracts of “Sleep Disturbance and Older Adults’ Inflammatory Response to Acute Stress,” “Interleukin-6 and Memory Functions of Encoding and Recall in Healthy and Depressed Elderly Adults,” and “Mitigating Cellular Inflammation in Older Adults: A Randomized, Controlled Trial of Tai Chi Chih” are posted at http://journals.lww.com/ajgponline/toc/2012/09000.
