The latest findings from the Atherosclerosis Risk in Communities (ARIC) Study indicate that people suffering chronic inflammation during middle age show a greater decline in cognitive function as they get older.
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When the body sustains an injury, it raises an acute inflammatory response to fight off infection and promote healing. This inflammatory response is localized and short-lived, and forms part of a healthy immune system.
In contrast, chronic inflammation is an unhealthy, low-grade inflammation that persists for months or even years at numerous sites throughout the body. This long-lived inflammatory response can be brought on by a number of factors, including psychological stress, pollution and autoimmune disorders such as rheumatoid arthritis. Chronic inflammation can cause joint pain or stiffness, digestive problems and fatigue.
Chronic inflammation is tough on the body, and can damage joints, internal organs, tissue and cells. It can also lead to heart disease, stroke and cancer. While other studies have looked at chronic inflammation and its effects on the brain in older people, our large study investigated chronic inflammation beginning in middle age and showed that it may contribute to cognitive decline in the decades leading up to old age."
Keenan Walker, Study Author
In the current study, scientists assessed changes in thinking and memory skills over 20 years in more than 12,000 people. On entry into the study, participants had an average age of 57 years and their blood levels of four biomarkers of inflammation (fibrinogen, white blood cell count, von Willebrand factor, and factor VIII) were measured.
Three years later, the level of C-reactive protein, another blood biomarker of inflammation, was measured. Participants were assigned to one of four groups according to the level of inflammation biomarkers in their blood.
Cognitive function was assessed using standardized tests of memory, processing speed and verbal fluency at the beginning of the study, six to nine years later, and around 20 years later. The data were adjusted for other factors that could affect thinking and memory skills, such as education, heart disease and high blood pressure.
The results showed that higher levels of inflammatory markers were associated with a steeper decline in cognitive ability. Inflammation was most strongly associated with declines in memory.
The group with the highest levels of C-reactive protein had a 12% steeper decline in thinking and memory skills than the group with the lowest levels. The difference between the groups with the highest and lowest levels of inflammation biomarkers was 8%.
Although the changes in thinking and memory skills associated with chronic inflammation were modest, they are greater than those associated with high blood pressure in middle age.
Many of the processes that can lead to a decline in thinking and memory skills are believed to begin in middle age, and it is in middle age that they may also be most responsive to intervention. Our results show that chronic inflammation may be an important target for intervention. However, it's also possible that chronic inflammation is not a cause and instead a marker of, or even a response to, neurodegenerative brain diseases that can lead to cognitive decline."
Keenan Walker, Study Author
The study shows that levels of inflammation in middle age are important factors in determining dementia risk. Reducing chronic inflammation, for example with regular exercise and a healthy diet, may help reduce cognitive decline.