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Fluid intelligence – the ability to creatively solve problems without prior knowledge or learning – declines with age, often as early as the third decade of life. Evidence from a new study suggests that body composition influences declines in fluid intelligence, and these declines may be related to immune system activation.
Body composition describes an individual’s body fat and lean mass. Excess body fat promotes systemic inflammation (which can promote neuroinflammation) and drives immune-related inflammatory processes. Lean muscle mass, however, may be protective against inflammation.
The study involved more than 4,400 middle-aged and older men and women living in the United Kingdom. The participants' body composition, cognitive function, blood leukocytes (white blood cells), and variables such as age, education level, and socioeconomic status were measured every other year for a period of six years.
The authors of the study found that higher levels of body fat, especially abdominal fat, were associated with greater losses of fluid intelligence. The losses appeared to be related to sex-specific increases in blood leukocyte counts and inflammation, as evidenced by higher levels of C-reactive protein.
These findings point to the importance of maintaining a healthy body weight throughout life as a strategy to reduce or prevent cognitive decline.