HDL and Cognitive Function in Older Adults: A Systematic Review

PURPOSE: The objective of this systematic review was to address the question, “Is High Density Lipoprotein-cholesterol (HDL-C or HDL) related to cognitive function in older adults?” MATERIALS AND METHODS: This systematic review included 17 primary research articles: 8 cross-sectional studies and 9 prospective studies that assess the relationship between HDL and cognitive function in older adults. The search for articles was conducted in July 2014 using online library resources at the UNT Health Science Center. The criteria for selection included (1) primary research articles that reported (2) a measure for HDL-C and (3) at least one measure for cognitive function (4) in older adults. Data was extracted using an individual article review form that assessed the research level, quality, and results for each article. Determination of the evidence base rating was based on the results across articles. RESULTS: The evidence base for the 8 cross-sectional studies did not support a relationship between HDL and cognitive function. However, these articles also did not address a change in cognitive function over time. The evidence from 9 prospective studies did support a relationship between HDL and cognitive function. Six of 9 studies reported baseline HDL levels significantly related to cognitive function. Five studies of 9 demonstrated a relationship between memory and HDL, and controlled for other influential factors, over a time range of 4-7 years. Another study demonstrated a relationship between HDL and language/sensory/motor functions at 16 years. The 4 studies that did not find significant relations had follow-up time periods of 3 years (2 studies), 12 years and 16 years, indicating that relations may be most evident within a limited window of time, and may vary by domain of cognitive function. CONCLUSIONS: The evidence base for prospective studies indicates a significant relationship between HDL and cognitive function. The results also suggest that some cognitive measures may not be equally informative across populations and/or languages. Future research studies should be a minimum of 4-years and extend beyond 16 years, with uniform sampling intervals. Additionally, future studies should control for domains of cognitive function, known factors that influence HDL-C, employ consistent sample and data collection processes, and include diverse populations.