Serum and macular response to carotenoid-enriched egg supplementation in human subjects: the Egg Xanthophyll Intervention clinical Trial (EXIT)

Abstract

The macular carotenoids lutein (L), zeaxanthin (Z) and meso-zeaxanthin (MZ) accumulate at the macula, where they are collectively referred to as macular pigment (MP). Augmentation of this pigment, typically achieved through diet and supplementation, enhances visual function and protects against progression of age-related macular degeneration. However, it is known that eggs are a rich dietary source of L and Z, in a highly bioavailable matrix. In this single-blind placebo-controlled study, L- and MZ-enriched eggs and control non-enriched eggs were fed to human subjects (mean age 41 and 35 years, respectively) over an 8-week period, and outcome measures included MP, visual function and serum concentrations of carotenoids and cholesterol. Serum carotenoid concentrations increased significantly in control and enriched egg groups, but to a significantly greater extent in the enriched egg group (P<0·001 for L, Z and MZ). There was no significant increase in MP in either study group post intervention, and we saw no significant improvement in visual performance in either group. Total cholesterol increased significantly in each group, but it did not exceed the upper limit of the normative range (6·5 mmol/l). Therefore, carotenoid-enriched eggs may represent an effective dietary source of L, Z and MZ, reflected in significantly raised serum concentrations of these carotenoids, and consequentially improved bioavailability for capture by target tissues. However, benefits in terms of MP augmentation and /or improved visual performance were not realised over the 8-week study period, and a study of greater duration will be required to address these questions.

Keywords: Meso-zeaxanthin; BCVA best-corrected visual acuity; CS contrast sensitivity; CisZ cis-zeaxanthin; EXIT Egg Xanthophyll Intervention clinical Trial; L lutein; MP macular pigment; MZ meso-zeaxanthin; TZ total zeaxanthin; WIT Waterford Institute of Technology; Z zeaxanthin; cpd cycles per degree; Carotenoid-enriched eggs; Cholesterol; Lutein; Macular pigment; Serum carotenoids; Zeaxanthin.

Fig. 1

Change in letter contrast sensitivity (CS) values between baseline and final visit (8 weeks) and at five different spatial frequencies: 1·20, 2·40, 6·00, 9·60 and 15·15 cycles per degree (cpd) using the Test Chart 2000 PRO^TM (Thomson Software Solutions) in the Egg Xanthophyll Intervention Trial; control egg group subjects; one standard egg per day. Enriched egg group subjects; one lutein:meso-zeaxanthin enriched egg per day. An improvement in CS at final visit in the enriched egg group relative to the control group is seen at 15·15 cpd reflected in the higher LogCS value. Values are means, with their standard errors. , Baseline visit; , 8-week visit.

Fig. 2

Change in best corrected visual acuity (BCVA) rating values between baseline and final visit (8 weeks) measured with Test Chart 2000 Xpert (Thomson Software Solutions) in the Egg Xanthophyll Intervention Trial; control egg group subjects (); one standard egg per day. Enriched egg group subjects (); one lutein:meso-zeaxanthin enriched egg per day. An improvement in BCVA at final visit in the enriched egg group relative to the control group is reflected in the higher visual acuity rating (VAR).

Fig. 3

Change in serum concentrations (µmol/l) of lutein (L), total zeaxanthin (TZ), cis-zeaxanthin (CisZ), meso-zeaxanthin (MZ) and zeaxanthin (Z) between baseline, midpoint (4 weeks) and final visit (8 weeks) using both reversed phase HPLC for L, TZ and CisZ analysis, and normal phase HPLC for Z:MZ ratio analysis on an Agilent 1260 Series system (Agilent Technologies Limited) in the Egg Xanthophyll Intervention Trial; control egg group subjects (); one standard egg per day. Enriched egg group subjects (); one L:MZ enriched egg per day. Increases in serum carotenoid levels can be seen at midpoint and final visits in the enriched egg group relative to the control group for L, TZ, CisZ and MZ, which are reflected in the higher concentration values seen. Increases in serum Z levels can be seen at midpoint in the enriched egg group relative to the control group, which are reflected in the higher concentration values seen. However, concentrations of Z were not significantly different between groups at final visit, reflected in the similarity of serum Z concentrations in both groups. Values are means, with their standard errors.

Fig. 4

Weekly analysis of egg yolk concentrations (µg/yolk) of lutein (L), total zeaxanthin (TZ), cis-zeaxanthin (CisZ) and meso-zeaxanthin (MZ) over a 7-week period using both reversed phase HPLC for L, TZ and CisZ analysis, and normal phase HPLC for MZ analysis on an Agilent 1260 Series system (Agilent Technologies Limited) in the Egg Xanthophyll Intervention Trial. Week-to-week variation can be seen by analysis of the trend in concentration values of both the control () and enriched () eggs.