Midlife plasma insulin-like growth factor I and cognitive function in older men.
BACKGROUND
Emerging biological and epidemiological evidence suggests possible benefits of higher IGF-I levels in cognitive aging.


OBJECTIVE
The objective of the study was to examine the relation of midlife plasma IGF-I levels to late-life cognition.


METHODS
We conducted a secondary analysis from the Physicians' Health Study II, a prospective cohort of U.S. male physicians. Participants provided blood samples from 1982 to 1984 (mean age 57 yr). Using stored samples, we measured free IGF-I in 376 men and total IGF-I and IGF binding protein-3 in 460 men. Starting in 2001, we administered telephone-based tests of general cognition [the Telephone Interview of Cognitive Status (TICS)], verbal memory, and category fluency. We estimated multivariable-adjusted mean differences in cognitive performance across levels of free IGF-I and IGF-I to IGF binding protein-3 molar ratio.


METHODS
Global score (averaging performance across all individual cognitive tests), the TICS, and a verbal memory score were measured.


RESULTS
Each sd increment in free IGF-I was associated with a multivariable-adjusted increase of 0.08 U (P = 0.02) on the global score. This mean difference was equivalent to that observed between men 2 yr apart in age: i.e. each sd increase in free IGF-I appeared cognitively equivalent to staying 2 yr younger. No significant mean differences in TICS scores were observed across free IGF-I levels. For verbal memory, each sd increment in free IGF-I was associated with an adjusted mean difference of 0.08 U (P = 0.03). Results appeared consistent for the molar ratio but were not statistically significant.


CONCLUSIONS
Higher midlife free IGF-I may be associated with better late-life cognition.
Okereke
Olivia I
OI
Division of Aging, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. ookereke@partners.org
Kang
Jae H
JH
Ma
Jing
J
Gaziano
J Michael
JM
Grodstein
Francine
F
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood* / Q000502:physiology; D016022:Case-Control Studies; D003071:Cognition / Q000502:physiology*; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D016037:Single-Blind Method
D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I