Relationships of body fat, retinal levels of lutein and zeaxanthin, and age-related maculopathy in the carotenoids in age-related eye disease study
Obesity may increase risk for age-related maculopathy (ARM), a disease affecting central vision, by reducing retinal lutein and zeaxanthin, where these carotenoids could be protective. An epidemiological approach was taken to investigate the relationships of body fat, retinal levels of lutein and zeaxanthin, and ARM in women participating in the Carotenoids in Age-Related Eye Disease Study (CAREDS).
No significant associations were observed between body mass index (BMI), waist circumference (WC), and waist-hip ratio (WHR) and prevalent ARM. Higher BMI was related to higher odds for early ARM (non-significant). Relationships of BMI to ARM were consistent with previous population studies, but were less consistent with WC and WHR.
Two studies were next undertaken to understand estimates of retinal lutein and zeaxanthin, or macular pigment. The first study evaluated reliability and within-person variability of macular pigment optical density (MPOD) and comparability between right and left eyes. The second study identified and described the determinants of MPOD in the CAREDS sample. Results of these investigations guided subsequent analyses and interpretations of associations of body fat and ARM.
Women with high body fat had significantly lower MPOD compared to lean women. Associations were similar among all body fat measures; however, WC was the strongest correlate of MPOD. Levels of MPOD were also observed to be lower among women with high compared to low WC, regardless of dietary lutein and zeaxanthin intake.
The hypothesis that high levels of MPOD are associated with lower odds for ARM was not supported in CAREDS. High compared to low MPOD was associated with higher odds for all types of early ARM. The associations differed significantly between middle and older-aged women, suggesting potential biases. Limiting the analyses to women with likely unstable diets due to chronic disease history reversed the associations (non-significant) and was consistent with a protective role of MPOD for ARM.
Future studies are needed to investigate the degree to which body fat impacts carotenoid metabolism and distribution in the blood and tissues. The inconsistent associations of MPOD to ARM among age-groups support the need for prospective longitudinal studies.