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

Brent J. Small, Ph.D.

Committee Member

Ross Andel, Ph.D.

Committee Member

Cathy L. McEvoy, Ph.D.

Committee Member

Sandra L. Reynolds, Ph.D.

Committee Member

Nagi B. Kumar, Ph.D., R.D., FADA.

Keywords

Cognitive Aging, Dietary factors, Healthy Aging

Abstract

Nutrition can be viewed as a modifiable factor related to maintaining and preserving health in older adults. Previous studies have found that nutritional factors can influence cognitive abilities, however few studies have examined macronutrients and micronutrients as they relate to cognitive functioning. Research has yet to examine the mechanisms related to nutrition, cognition and aging in an older adult population from a holistic and interactive perspective.

This dissertation examined three research questions to better understand the relationship between age, nutrition, cognition, and inflammatory biomarkers. First, is nutrition related to cognition beyond demographic factors? Do individual nutrients serve as mediators? Second, are inflammatory biomarkers significant mediators to cognitive performance? Third, do nutrients and inflammatory markers interact as moderators to cognitive performance?

This study examined 1,317 adults 60 years and older from the National Health and Nutrition Examination Survey III (NHANES III). Macronutrients were collected from a retrospective 24-hour dietary recall, micronutrient values were obtained from blood serum/plasma for vitamin C, vitamin D, vitamin E, homocysteine, iron, folate, and inflammatory biomarkers values were obtained from blood serum/plasma for C-reactive protein, fibrinogen, and ferritin. Cognition was measured by 6 tasks: immediate and delayed word recall, immediate and delayed story recall, orientation, and digit subtraction. All tasks were then combined to form a global cognitive measure.

Results for question one found that after controlling for age, sex, education, and total calorie intake, higher intake of polyunsaturated fat was related to better global cognition and delayed story recall score (std β= .08, p= .028, std β= .08, p=.04 respectively). Greater than 28% of calories from carbohydrate indicated worse global cognition and delayed story recall (std β= -.013, p= .028, and std β= -.158, p= .01). Higher intake of saturated fat and protein were related to worse digit subtraction scores (std β= -.160, p= .02, std β= -.064, p= .02). Higher serum vitamin C, D, and folate levels were related to better global cognition and digit subtraction. Additionally, higher serum vitamin C and D were associated with better orientation score, and folate was related to better immediate and delayed story recall. Building from these relationships, individual mediation models found that serum vitamin C, vitamin D, folate, and ferritin were significant mediators between age and the previously mentioned cognitive tasks.

Results for question two examined mediation between inflammatory markers and cognition and found that higher fibrinogen was related to worse global cognition and digit subtraction. Higher ferritin was associated with better delayed word recall.

Question three investigated the moderating relationship between age, nutrients, and biomarkers, and results found that folate and fibrinogen were significant moderators. Higher serum folate was related to better global cognition and immediate story recall. Ferritin values below 1.2 and above 3.2g/l indicated worse digit subtraction performance. Evidence for a dose-dependent relationship was confirmed.

Results from this project demonstrated that select nutrients (polyunsaturated fat, vitamin C, D, and folate), and inflammatory markers (ferritin and fibrinogen) were associated with cognitive performance across various cognitive domains. Consuming a diet rich in healthy fatty acids, and antioxidants may be beneficial for cognitive health. Future studies should continue to examine the underlying mechanisms connected to maintaining, preserving, and protecting cognitive abilities in older adults.

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