Graduation Year

2015

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

School of Aging Studies

Major Professor

Ross Andel, Ph.D.

Co-Major Professor

Alyssa Gamaldo, Ph.D.

Committee Member

Ross Andel, Ph.D.

Committee Member

Alyssa Gamaldo, Ph.D.

Committee Member

Theresa M. Beckie, Ph.D.

Committee Member

William E. Haley, Ph.D.

Committee Member

Cathy L. McEvoy, Ph.D.

Keywords

Aging, Cardiovascular, Cholesterol, Elderly, Lipids

Abstract

Cardiovascular health is a major determinant of quality of life and mortality, especially in older adulthood. With the world’s oldest population increasing at expedited rates, challenges from cardiovascular conditions and its implications are spawning. Although it is well known that dyslipidemia may lead to cardiac events, less is known about the effects on cognitive and physical function in older adults. Epidemiological studies show that optimizing current preventive strategies even at older ages may reduce the incidence of cardiovascular comorbidity (e.g. hypertension, stroke) and increase quality of life. Determining the association between lipoproteins and cognitive and functional performance in older adults may help develop interdisciplinary interventions designed to maintain independence longer and improve the overall quality of life.

The current dissertation contains two studies examining serum lipoproteins, specifically total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), and high-density lipoprotein cholesterol (HDL-C) in older adults in relation to cognitive and functional outcomes. The first study examined the association between lipoproteins and cognitive performance in a cognitively normal older adult population. Results showed an association between low levels of TG and higher composite cognitive scores (CCS), but this association disappeared when apolipoprotein ε4 allele (APOE ε4 allele) was adjusted for in the model. High levels of HDL-C were also associated with the CCS and this association remained significant even after adjusting for APOE ε4 allele. Furthermore, these associations were only significant among women. High HDL-C remained linked with visuospatial function and attention and working memory even after adjusting for APOE ε4 allele. Further moderation analysis indicated that the association between TGs, HDL-C and cognitive performance was moderated by the APOE ε4 allele. Stratification by carriers and non-carriers of the ε 4 allele indicated that the previous association was only significant for non-carriers.

The second study of this dissertation is a longitudinal analysis, which explored the association between TC, LDL-C, TG and HDL-C and physical function. Random effects analysis was used to assess whether lipoprotein levels affect subsequent change in physical function. All models were adjusted for baseline age, sex, education, and perceived current economic situation, cardiovascular risk factors and comorbidity inclusive of cognitive disability. Results showed that lower levels of TC and HDL-C had cross-sectional associations with more ADL disability but not longitudinally, and higher levels of TG were related to better grip function. Moderation analysis of the previous significant association indicated that only cognitive disability moderated the cross-sectional association between TC and for ADLs. Further stratification showed that the association was only pertinent for participants with cognitive disability. Independent of cardiovascular risk factors and an extensive list of comorbidities, older adults living in the community with higher levels of TC, TG and HDL-C were associated with better physical function outcomes. Lipid patterns in older adults may be indicative of physical function and may serve clinicians as a tool to compress morbidity in older adults and help them maintain independence and a high quality of life for as long as possible.

In conclusion, lipid levels in older adults play an important role in maintaining cognitive and physical function into older ages, thus maintaining a good quality of life. Higher HDL-C seemed to be the lipid associated with maintaining cognitive function, while TC dominated the association with physical function.

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