- Click here for explanation of classification scheme.

To evaluate the relationship between dietary lutein plus zeaxanthin and intermediate age-related macular degeneration (AMD).

• Women enrolled in the Women's Health Initiative (WHI) at three of 40 sites
• Had intakes of lutein plus zeaxanthin that were above the 78th or below the 28th percentiles as assessed at baseline enrollment into WHI from 1994 to 1998.

Women were excluded if they had medical conditions that predicted survival of less than three years, such as alcoholism, drug dependency or mental illness.

Recruitment

Women with high and low intakes of lutein plus zeaxanthin at baseline in the WHI Observational Study were recruited four to seven years later into the CAREDS when the presence of AMD was determined by fundus photographs.

Design

Prospective cohort study.

Statistical Analysis

• Unpaired two-tailed T-tests, analysis of covariance and x² tests to assess the statistical significance of potential covariates in the high vs. low lutein plus zeaxanthin intake groups and by the presence or absence of AMD
• Odds ratios (ORs) and 95% confidence intervals (CIs) for specific AMD end points were calculated comparing the high lutein plus zeaxanthin intake group with the low intake group by means of logistic regression
• Variables that were statistically significant related (P≤0.1) to both the AMD and lutein plus zeaxanthin intake group in CAREDS or that were previously suspected to be biologically plausible confounders were tested by adding them singly to age-adjusted models.

 

Timing of Measurements

• Diet was assessed at WHI baseline (1994-1998) and 15 years before CAREDS baseline (1986-1989) by means of a previously validated, semi-quantitative food frequency questionnaire (FFQ).  The 15-year past FFQ was administered at CAREDS baseline (2001-2004).
• Serum samples were obtained from participants at WHI baseline examinations (1994-1998)
• Stereoscopic color fundus photographs were taken at CAREDS baseline (2001-2004) examinations.

Dependent Variables

• Age-related macular degeneration
• Serum values: 
  • Total cholesterol (mg per dL)
  • Triglycerides (mg per dL)
  • Lutein (all-trans) (μmol per L)
  • Zeaxanthin (trans) (µmol per L)
  • Lutein + zeaxanthin (trans) (µmol per L)
  • Median serum lutein + zeaxanthin (trans) (µmol per L)
  • x~Tocopherol (mg per dL)
  • y~Tocopherol (mg per dL).

Independent Variables

• Lutein and zeaxanthin
• Total energy (kcal), total dietary fat (percent of kcal), saturated fat (percent of kcal), polyunsaturated fat (percent of kcal), trans-fat intake (mg per day), total omega-3 fatty acids (g per day), dietary fiber (g per day), alcohol intake (g per day), fruit intake (servings per day), vegetable (servings per day), β-Carotene (µg per day), β-Cryptoxanthin (μg per day), vitamin C (mg per day), vitamin E (mg per day), y~tocopherol (mg per day), zinc (mg per day)
• Among supplement users percentage: Multivitamins, lutein or lutein + zeaxanthin, high-dose antioxidants, high dose zinc.

Control Variables

• Age group percentage: 69 or less, 70 to 74, 75 or more
• Ethnicity: Percentage White
• Education percentage: High school, college, post-college studies
• Income percentage: More than $75,000
• Study site: Iowa, Oregon, Wisconsin
• Smoking pack-year percentage:  Never, zero to seven, more than seven
• Alcohol g per day: zero, more than zero to less than for, more than four
• Sunlight exposure Maryland sun-year: Total last 20 years, intermittent last 20 years, lifetime average exposure
• Physical activity: METs per week.

• Initial N: 1,894
• Attrition (final N): 1,787 consisting of 918 in the low intake group and 869 in the high intake group.

Age 

• Low intake group: 52%, 69 years or younger; 24%, 70 to 74 years; 24%, 75 years or older
• High intake group: 48%, 69 years or younger; 24%, 70 to 74 years; 28%, 75 years or older.

Ethnicity

• Low intake group: 98% white
• High intake group: 97% white.

Other Relevant Demographics

• AMD outcomes, low intake group: 19%, any; 15%, large drusen; 10%, pigmentary abnormalities; 2%, advanced AMD
• AMD outcomes, low intake group: 18%, any; 14%, large drusen; 11%, pigmentary abnormalities; 1.7%, advanced AMD

Location

• The University of Wisconsin (Madison WI)
• The University of Iowa (Iowa City)
• The Kaiser Center for Health Research (Portland OR).

Distribution of Risk Factors By Level of Lutein Plus Zeaxanthin in the Diet

• The median level of lutein plus zeaxanthin in the diet was approximately three times higher in women in the high lutein intake group than in those in the low intake group
• Women in the high lutein intake group were likely to be:
  • Older, non-white (P≥0.05), college educated, in a higher income bracket and more physically active (P≤.001) and to have a lower body mass index, waist-hip ratio, waist circumference and serum triglyceride levels (P≤0.001) than those in the low lutein intake group
  • They were also more likely to rate their general health status as excellent or very good (P≤0.001)
  • Total energy intake was higher as well as intake of dietary fiber, fruits, vegetables, many micronutrients and carotenoids (P≤0.001) and alcohol (P<0.01) was higher in this group.

Association Between Dietary Lutein Plus Zeaxanthin Levels and Intermediate AMD

• The prevalence of overall intermediate AMD was not statistically different between the high and low lutein intake groups after adjusting for age. Adjustments did not produce statistically signficant results for:
  • AMD risk factors
  • Excluding women with a previous diagnosis of AMD
  • Adding total energy intake
  • Examining quintiles of dietary lutein plus zeaxanthin
• When reviewing the association between lutein plus zeaxanthin levels and AMD in women whose intakes had not changed more than one quintile between the CAREDS 15 year past FFQ and the WHI baseline FFQ, the younger age group (less than 75 years) stronger inverse relationships for all types of AMD were seen. Substantially lower ORs in the overall sample and in women younger than 75 years were found when women were excluded with a history of cardiovascular disease, diabetes, hypertension or previously diagnosed AMD:

	Age Adjusted Model OR (95% CI)	Further Excluding Women at Risk for Diet Change OR (95% CI)
Any intermediate AMD  Overall sample	0.97 (0.75-1.23)	0.81 (0.53-1.25)
Any intermediate AMD   Less than 75 years	0.81 (0.59-1.11)	0.57 (0.34-.95)
Large drusen Overall sample	0.92 (0.7 to 1.21)	0.79 (0.48 to 1.29)
Large drusen Less than 75 years	1.26 (0.82 to 1.95)	0.52 (0.28 to 0.97)
Pigmentary abnormalities Overall sample	1.03 (0.75 to 1.43)	0.88 (0.49 to 1.57)
Pigmentary abnormalities Less than 75 years	0.86 (0.56 to 1.3)	0.61 (0.30 to 1.25)

Effect of Sunlight on the Relationship Between Dietary Lutein Plus Zeaxanthin Levels and Intermediate AMD 

Because lutein and zeaxanthin might protect in part by absorbing the energy of sunlight, the possibility that the association between dietary lutein plus zeaxanthin and intermediate AMD differed in women whose average annual sunlight exposure during the past 20 years was above the median vs. below (P for interaction = 0.07).

• In the youngest age group, the association between lutein and intermediate AMD was similar regardless of sunlight exposure (ORs and 95% CIs in those above and below the median for sun exposure 0.8 (0.52 to 1.24) and 0.82 (0.53 to 1.29) and did not differ from the age-adjusted estimate for women younger than 75 years
• The OR in the overall sample was significantly protective after exclusion of women with recent diet instability or who were at risk for diet change, but only in those with relatively low sun exposure (OR, 0.54; 95% CI: 0.3 to 0.99)
• Results in women younger than 75 years were similar to those  seen in other aspects of the study, but the point estimate was lower in women below the median for sun exposure (OR, 0.52; 95% CI: 0.25 to 1.08) vs. above the median (OR, 0.61; 95% CI: 0.29 to 1.28).

Association Between Specific Food Sources of Lutein Plus Zeaxanthin and Intermediate AMD

• No statistically significant estimates or trends were observed in either age or multivariate adjusted models
• Stratifying by age did not significantly change the results (P for interaction = 0.89). Similar results were found for serum lutein and serum zeaxanthin levels evaluated separately
• A stronger protective association was found in the sub-sample of the youngest women at risk for AMD (less than 75 years) who also reported stable intake of lutein plus zeaxanthin and did not report comorbidities that increased their risk of previous diet change, but only in the highest quintile and it was not statistically significant. 

Nutrient Index and Intermediate AMD

A nutrient index was created to compare the possible effect of other nutrients on the relationship between lutein plus zeaxanthin intake and AMD. Persons were classified with generally healthy or generally unhealthy intakes of nutrients that have been associated with AMD. 

• Although not statistically significant, the ORs were all in a protective direction
• The lowest OR was observed in women with low intake of lutein plus zeaxanthin but high intakes of vitamin E and zinc with low intake of polyunsaturated fats (N=26) compared with women with poor intakes of lutein, vitamin E and zinc  and high intake of polyunsaturated fats. Low levels of reporting prevented further levels of exploratory analysis.

Association Between Lutein Plus Zeaxanthin Levels and Advanced Age

• No statistically significant associations were observed between dietary lutein plus zeaxanthin levels and advanced AMD in the overall sample
• ORs were in a protective direction in younger women, particularly after exclusion of women who had changed their diets between the CAREDS 15 year past FFQ and the WHI baseline FFQ
• Direct associations between serum lutein level and advanced AMD with statistically significant trends were observed. Further exploratory analyses were not conducted because of the limited number of advanced AMD cases (N=34) in CAREDS. 

• The hypothesized association between dietary lutein and zeaxanthin intake and the prevalence of AMD in the full study sample of women age 50 to 79 years was not found
• Secondary analysis disclosed a statistically significant protective association in women younger than 75 years with stable intake of lutein plus zeaxanthin without a history of cardiovascular disease, diabetes, hypertension or previously diagnosed AMD. Similar protective associations were observed for large drusen. Although not statistically significant, associations in this sub-sample were in the protective direction for the more advanced lesions of pigmentary abnormalities as well as advanced AMD. The strongest inverse associations were observed between intermediate AMD and high intake of vegetables in general as well as green vegetables.
• The body of evidence from experimental and observational studies supports a protective relationship between lutein and zeaxanthin levels and AMD. People with AMD have lower concentrations of lutein and zeaxanthin in their macular than those without AMD. Lower levels of these carotenoids have also been found in autopsy specimens of donor eyes with AMD.
• Epidemiologic studies of early and intermediate AMD do not support the hypothesis of a beneficial role of lutein and zeaxanthin and the null association observed in this study in the primary analysis is consistent with few previous studies. It is possible that studies of early and intermediate AMD are not in agreement with overall literature because of inconsistencies in the measurement of and adjustment for other potential risk factors. CAREDS collected data on most known potential risk factors for AMD, but inclusion of these factors as covariates in statistical models has little effect on estimates of risk. 
• Associations between dietary lutein plus zeaxanthin intake and intermediate AMD were in the hypothesized protective direction in women younger than 75 years; although, not statistically significant. The critical window of exposure to dietary and other factors for development of AMD is unknown. The results of this study suggest that future research should examine the relationship between AMD and dietary factors such as lutein and zeaxanthin intake in more specific subgroups than in past studies. 
• Several studies have shown a lack of a consistent relationship between serum levels of lutein and zeaxanthin and AMD. This suggests that dietary lutein and zeaxanthin intake levels may be a marker for other dietary attributes that protect against AMD. Also, it is possible that there are combinations of foods that provide the optimal mix of nutrients to protect against AMD. It will be challenging for other studies to evaluate the individual or joint benefits of potentially protective nutrients or whether high intakes of certain nutrients can compensate for low intakes of others.
• More conclusive evidence from long-term prospective studies and clinical trials is needed to determine whether the intake of macular carotenoids themselves or as markers of broader dietary patterns can protect against intermediate AMD or delay progression in individuals who have early stages of the disease.

Government:	National Institutes of Health
Other:	Research to Prevent Blindness

The authors note the following limitations:

• Non-participation bias was a concern with this study because 36% of those eligible to participate in CAREDS declined. Since healthier people are more likely to participate in health studies such as the WHI, the associations in the study may be biased toward the null if those who did not participate had more AMD.
• There was evidence that diet instability may have biased the associations and with the possibility of selective mortality bias, which may explain the study's inability to detect the hypothesized association overall
• Although numerous analysis were performed in this study, the results could have been due to chance.