"Cognitive health in old age may be related to cardiovascular risk factors such as serum lipid levels, but how lipids relate to cognitive change is unclear," say Chandra Reynolds (University of California at Riverside, USA) and co-authors.
They carried out a 16-year longitudinal study of 819 adults, aged 50 years or above at baseline, from the Swedish Adoption Twin Study of Aging. The cohort included 21 twin pairs who were discordant for dementia.
In-person testing of cognitive function was carried out by the researchers at baseline during 1986–1988. The same tests were then carried out on four more occasions at 3–7 year intervals, with a total observation span of approximately 16 years. Blood samples taken at these sessions were also used to measure serum lipids.
Reynolds and team found that high high-density lipoprotein (HDL) cholesterol was associated with better cognitive ability before the age of 65 years and greater maintenance of ability at older ages in women, but not men. Apolipoprotein (apo)A-I effects were similar to HDL cholesterol in women and men.
High values for apoB predicted better cognitive function in men, although this showed a decline with age suggesting diminishing benefits of higher apoB values. In women, high rates of apoB predicted faster rates of decline in cognitive ability at age 65 or above.
In men, high total cholesterol was associated with better performance but faster rates of cognitive decline before the age of 65 years. No significant effects of total cholesterol on cognitive function were seen in women, however.
Elevated triglycerides predicted worse performance and faster cognitive decline before the age of 65 years in men, but this was not significant after adjustment for confounders. In women, low triglycerides predicted greater cognitive ability before the age of 65 years and better maintenance of ability at older ages.
In the twin pairs who were discordant for dementia, higher total cholesterol and apoB were recorded in the twin who subsequently developed dementia than in the one who did not.
"High lipid levels may constitute a more important risk factor for cognitive health before age 65 than after," conclude the authors.
"Findings for women are consistent with clinical recommendations, whereas for men, the findings correspond with earlier age-associated shifts in lipid profiles and the importance of lipid homeostasis to cognitive health."
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