"This exploratory observation is consistent with a broad body of evidence from observational and experimental studies that suggests that these carotenoids may protect against AMD," wrote lead author Suzen Moeller from the University of Wisconsin.
AMD affects the central part of the retina called the macula, which controls fine vision, leaving sufferers with only limited sight. AMD affects over 30 million people worldwide, and is the leading cause of blindness in people over 50.
Previous studies have reported a link between AMD and lutein and zeaxanthin, found in leafy green vegetables, corn, egg yolks, squash, broccoli and peas. The carotenoids are proposed to reduce the risk of AMD by absorbing blue light that could damage the macula, by preventing free radicals from damaging eye cells and by strengthening eye cell membranes.
The Carotenoids in Age-Related Eye Disease Study (CAREDS), published in the American Medical Association's Archives of Ophthalmology (Vol. 124, pp. 1151-1162), used a cohort of 1787 women aged between 50 and 79. Dietary assessments were performed by means of a semi-quantitative food frequency questionnaire (FFQ) at the start of the study. A FFQ also assessed dietary intake over the 15 years before the start of the study.
Blood samples were taken to assess levels of carotenoids and colour photographs of the retina were used to determine the presence and progression of AMD.
While no significant difference in the risk of AMD was observed for the overall sample population, the researchers found that women under 75 with a high and stable intake of lutein plus zeaxanthin (2868 micrograms per day) had a 43 per cent lower risk of intermediate-stage AMD, compared to under 75s with low lutein plus zeaxanthin intake (792 micrograms per day). This results did not include women with diet instability.
High and stable intake of lutein plus zeaxanthin was associated with a 74 per cent lower risk of late-stage AMD, compared to under 75s with low lutein plus zeaxanthin intake.
Women over 75 with high intakes of lutein plus zeaxanthin did not have reduced risks of AMD, compared to the lower intake group of the same age.
Blood levels of these carotenoids were not associated with a decreased or increased risk of AMD, said the researchers.
"We did not observe the hypothesised association between dietary lutein and zeaxanthin intake and prevalence of intermediate AMD in the full study sample of women aged 50 to 79 years," wrote Moeller. "However, secondary analyses disclosed a statistically significant, protective association in women younger than 75 years with stable intake of lutein plus zeaxanthin."
The lack of a link between intake of carotenoids and AMD in the overall study group could be due to several factors, said Moeller, including the fact that the older women who participated in the study may have been more likely to have consumed higher levels of fruits and vegetables during their lifetimes than other older adults who have already died.
There are several limitations with this study, namely that dietary assessment was done by a FFQ, a semi-quantitative measure that relies on the recall and accuracy of the individual. Also, by asking volunteers to evaluate dietary intake over the 15 years previous to the start of the study will undoubtedly introduce errors.
Moreover, the estimates of lutein plus zeaxanthin would also include intakes of nutrients that go along with carotenoid-rich foods, such as other vitamins and minerals that were not assessed.
"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," said Moeller.
Public awareness of lutein has never been higher in Europe, with a recent survey, from Frost and Sullivan and commissioned by Kemin, finding that awareness has doubled compared to last year, to 25.8 per cent and 16 per cent in Italy and France, respectively.
Germans showed the greatest awareness, of 33.3 per cent. The UK was the only country where it seemed to have slipped slightly, to 20 per cent (compared to 25.8 in 2005).
However, the same survey also found that awareness of AMD was relatively low with only 33 per cent of French respondents having heard of it, compared to 27 per cent in Italy, 24 per cent of Germans, and 21 per cent in Portugal.
The exception was the UK, where 41 percent of respondents questioned had heard of AMD.