The Ratio of HDL to LDL in Serum Is Related to Macular Pigment Density and Cognitive Function in Older Adults: Potential Insights into Lutein Transport to Neural Tissue

Abstract

The dietary carotenoid, lutein, is selectively taken up into neural tissue. Neural lutein is related to better cognition. However, serum lutein concentrations may not accurately reflect neural levels. Lutein is mainly transported on high‐density lipoprotein (HDL) followed by low‐density lipoprotein (LDL). HDL may play a significant role in delivery of lipophilic nutrients to neural tissue. Therefore, lutein content on HDL may better reflect neural levels. However, this has yet to be investigated in humans. The relative amounts of HDL and LDL (HDL/LDL) is an indicator of the distribution of lutein in the circulation. The aim of this study was to determine the relationship between changes in lipoprotein profiles, neural lutein concentration (measured by macular pigment density, MPD), and cognitive performance in older adults (n=31) using a previously conducted study in which participants were followed for 6 months. Serum collection, MPD (using heterochromatic flicker photometry), and cognitive testing (computerized cognitive assessment battery, CANTAB) were performed at baseline, 3 months, and 6 months. Serum lipoproteins and carotenoids were determined using an enzymatic colorimetric method and HPLC, respectively. There was a group of individuals who had MPD increases >0.10 optical density (OD) over the study period (n=17). These subjects were classified as “MPD responders”. In these subjects, adjusting for age, change in HDL/LDL was positively associated with change in MPD (r=0.66, p=0.006) and the strength of this association was greater in a subset of MPD responders who also had increases in serum lutein (n=10, r=0.77, p=0.01). The association between change in HDL/LDL and MPD was not significant in MPD responders without increases in serum lutein. In all MPD responders, change in both HDL/LDL and MPD were positively associated with change in spatial working memory and increased spatial planning, while change in serum lutein was positively related to spatial planning only (adjusted for age and education, P<0.05). Associations between HDL/LDL and cognition were stronger in the subset of MPD responders who also had increases in serum lutein (P<0.05). In MPD non‐responders (ΔMPD ≤0.05 OD), HDL/LDL was not related to MPD, but was associated with spatial planning. Collectively, these findings lend support to the hypothesis that lutein carried on HDL is targeted to neural tissue and may be important for cognition.Support or Funding InformationThis work was supported by the Hass Avocado Board and USDA (1950‐51000‐087)