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1 From the Vision Science Laboratory, University of Georgia, Athens, Georgia; the 2 Retina Service, Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, Indiana; and the 3 Schepens Eye Research Institute, Boston, Massachusetts.
| Abstract |
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METHODS. Six hundred eighty subjects were tested. Information on MPOD, body mass index (BMI), body fat percentage (n = 400, using bioelectric impedance), dietary intake (n = 280, using a food frequency questionnaire), and serum carotenoid content (n = 280, using reversed phase high-performance liquid chromatography) was obtained.
RESULTS. There was an inverse relationship between MPOD and BMI (n = 680, r = -0.12, P < 0.0008) and between MPOD and body fat percentage (n = 400, r = -0.12, P < 0.01). These relationships were largely driven by data from the subjects with higher BMI (more than 29, 21% less MP) and higher body fat percentage (more than 27%, 16% less MP). Dietary carotenoid intake and serum carotenoid levels were also lower in subjects with higher BMI (n = 280).
CONCLUSIONS. Obese subjects tend to have lower retinal L and Z. This reduction may be due to decreased dietary intake of L and Z and/or competition between retina and adipose tissue for uptake of L and Z.
| Introduction |
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In the present study, we tested the hypothesis that body composition is related to tissue concentrations of carotenoids in the central retina by comparing body fat percentage and BMI with macular pigment optical density (MPOD), which is a measure of L and Z in the retina.12 In our initial study,13 we found no relationship between body composition and MPOD. This null finding, however, may have been due to a lack of statistical power because of the small sample size (N = 13). Thus, in the present study we extended the analysis to a larger sample (N = 680), tested at two different geographic locations, and found that individuals considered obese have lower MPOD.
| Methods |
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Two female subjects, one from each sample, with BMIs of 68 and 73 were excluded from further statistical analysis due to extreme values. These subjects had MPODs (460 nm, 1° test stimulus) of 0.0 and 0.08, respectively. The study followed the tenets of the Declaration of Helsinki. All procedures were approved by the institutional review board at the University of Georgia and the Indiana University School of Medicine, and informed consent was obtained from each subject before testing.
Anthropometric Assessment
Information on BMI (body weight in kilograms divided by height
in meters squared) was obtained from all subjects. Height and weight
were determined at the time of the session using a calibrated,
dual-reading, heavy-duty die-cast beam scale. Body fat percentage was
assessed only in the subjects tested at the Georgia site. This
assessment was performed using bioelectric impedance (Omiron analyzer,
HBF 300; Carolina Biological Supply, Burlington, NC). Evidence has
indicated that bioelectrical impedance analysis is
reliable15
and correlates highly with other methods of
estimating body fat percentage, such as hydrodensitometry and skinfold
calipers (Pearsons r = 0.810.86). To assess the
reliability of the specific instrument at the Georgia site, we measured
four subjects (two males, two females) on 20 separate occasions over a
period of 2 months, under various conditions (before and after meals,
at various levels of hydration, for example). The average body fat
percentage of each of the subjects was 8.0% ± 0.6%, 13.2% ±
0.41%, 15.4% ± 0.4%, and 21.0% ± 0.55% with an absolute range of
approximately 2%, indicating that our measurement device was reliable.
Dietary and Serum Carotenoid Analyses
Dietary and serum carotenoid data were collected only on the 280
subjects who were tested at the Indianapolis site. The equipment and
procedures used in these assessments are detailed in Ciulla et
al.14
and are described briefly in this report.
For dietary assessment, a 1-year food frequency questionnaire (FFQ) was used that assesses usual intake of 122 food items.16 The analysis of these FFQs was performed at the Fred Hutchinson Cancer Research Center (Seattle, WA). The serum carotenoid analysis was conducted using a gradient reversed phase HPLC system with a photograph diode array detector set (HP 1100; Hewlett Packard, Burlington, MA) at 425 nm and a C18 guard column.14
Assessment of MPOD
MPOD was measured in the right eye only of each subject, by
using a common psychophysical method based on flicker
photometry.17
This method is reliable,17
correlates well with physical estimates of the pigments,18
and yields optical densities that correspond to chemical concentrations
of the pigments.12
The apparatus and stimuli used for the
measurements are fully described and schematized in Wooten et
al.19
This same design and procedure was used at both the
Georgia and the Indianapolis sites.
MPOD was measured with a 1° test stimulus. Test stimuli were presented in natural view and near the center of a 6°, 10.5-cd/m2, 470-nm circular background. The test stimulus was alternately composed of a 458-nm measuring field (peak MP absorbance) and a 570-nm, 16.7-cd/m2 reference field (minimal MP absorbance). Light for the measuring and reference fields and the background was produced by 40-nm band-pass LEDs with peak energy at 458, 570, and 470 nm (Nichia Corp., Mountville, PA). This measurement was obtained in the fovea (where MP is the most dense) and 4° in the parafovea (where light absorption by MP is negligible). A tiny (5-minute) opaque fixation point was located on the left edge of the background, and subjects fixated this point when making the parafoveal measurement. The measuring and reference fields were superposed and presented out of phase at an alternation rate of 11 to 12 Hz in the foveal condition and 6 to 7 Hz in the parafoveal condition. Subjects adjusted the radiance of the 458-nm measuring field to achieve minimal flicker with the 570-nm reference. Subtracting the foveal from the parafoveal sensitivity measurement yields an optical density measure of MP.17 Subjects were given brief instructions on the method and a practice trial before five foveal and five parafoveal measurements were made. The foveal and parafoveal values were calculated from the average of the final five readings, and these averages were then used to calculate MPOD.
| Results |
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| Discussion |
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There was no relationship between MP and adiposity when only subjects with a BMI below 29 and body fat below 27% were considered. Our analysis further suggests that the relationship between higher body fat and BMI and MPOD is not related to gender. Both males and females with higher body fat and BMI tended to have lower MPOD. Nonetheless, because females also tend to have higher average body fat, an effect of obesity on MPOD would affect a larger number of females.
There are at least two possible nonexclusive explanations for our results. First, adipose tissue could compete with the retina for uptake of L and Z, resulting in less incorporation in the retina and lower MPOD. If competition takes place, then the effect is clearly not linear. An effect of adiposity is only seen when obese subjects are included in the sample. Moreover, the relationship between serum L and Z and MPOD was stronger in the subjects with higher BMI (>29).
The second factor influencing the relationship between adiposity and MPOD is probably the subjects dietary patterns. Past studies have shown that both MPOD22 23 and BMI7 are related to dietary intake of L and Z. Higher body fat percentage has also been associated with poor dietary habits.24 Our present analysis also showed that those subjects with higher BMI had lower MPOD and decreased L and Z intake. Thus, a poor diet could promote both obesity and lower MPOD.
Nonetheless, an analysis of the Indianapolis sample (see Table 1 ) suggests that the small differences in blood L and Z concentrations related to differences in diet are not sufficient to account for the 18% difference in MPOD found between subjects with low versus high BMI. For example, the regression line relating serum L and Z to MPOD predicts that the serum values would have to double to produce the 18% change seen in MPOD (see Fig. 3 in Ciulla et al.14 ). Thus, some factor associated with higher adiposity (e.g., competition for L and Z uptake), in addition to diet, may have contributed to the observed MP differences.
Past epidemiologic data have linked obesity to risk of age-related macular degeneration (AMD)25 26 and age-related cataract.27 Recent studies suggest that reduced MP is associated with greater risk for AMD28 and cataract.29 30 Thus, it is important to consider MPOD as one of multiple linked variables that may contribute to risk for eye disease in obese individuals.
| Footnotes |
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Submitted for publication June 1, 2001; revised August 27, 2001; accepted September 14, 2001.
Commercial relationships policy: F.
The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked "advertisement" in accordance with 18 U.S.C.
1734 solely to indicate this fact.
Corresponding author: Billy R. Hammond, Jr, Vision Science Laboratory, University of Georgia, Athens, GA 30602; bhammond{at}egon.psy.uga.edu.
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