Plasma IGF-I levels and cognitive performance in older women

Background Emerging biologic and epidemiologic evidence suggests benefits of insulin-like growth factor-I (IGF-I) in cognitive aging. Objective To examine the relation of circulating IGF-I to cognition. Methods We measured plasma IGF-I and IGF-binding protein-3 (IGFBP-3) in 590 women aged 60–68 years. An average 10 years later, we administered telephone-based tests of general cognition (Telephone Interview of Cognitive Status [TICS]), verbal memory, category fluency, and attention. We estimated multivariable-adjusted mean differences in performance across levels of IGF-I/IGFBP-3 molar ratio. Results On the TICS, each standard deviation (S.D.) increase in molar ratio was significantly associated with better performance: multivariable-adjusted mean difference = 0.2 units, 95% confidence interval (0.0,0.4), p = 0.05. This effect estimate for each S.D. increase in molar ratio was cognitively equivalent to the mean difference we observed on the TICS between women 1 year apart in age. On a global score combining all tests, there was also a trend of better performance with each S.D. increase in molar ratio (p = 0.07). IGF-I levels were not associated with performance in verbal memory. Conclusions Higher IGF-I levels may be associated with better general cognition.