Increased intakes of the carotenoids were associated with a 26% reduction in the risk of late-stage AMD, but a non-significant 4% reduction was observed for the early stages of the disease, researchers from Peking University report in the British Journal of Nutrition.
“The present systematic review and meta-analysis demonstrates that, on the basis of evidence available to date, dietary intake of lutein and zeaxanthin is not significantly associated with a decrease in the risk of developing early AMD, whereas an increase in the intake of xanthophylls may have beneficial effects for late AMD,” wrote the researchers.
The Chinese researchers limited their study to studies that analyzed dietary intakes and not the use of supplements.
“It should also be noted that there are only a few studies that have examined this association, which limits the power of meta-analysis.”
Lutein and zeaxanthin in the eye
The macula is a yellow spot of about five millimeters diameter on the retina. As we age, levels of the pigments in the macula decrease naturally, thereby increasing the risk of AMD. The yellow color is due to the content of the carotenoids lutein and zeaxanthin, which we derive from the diet.
These compounds are the only carotenoids capable of filtering the harmful blue light than can damage cells in the eye, the rods and the cones.
A thin macular pigment can allow the blue light through and destroy the cells. Maintaining high levels of both carotenoids, and therefore the macular pigment, is a valid approach to maintaining eye health and reducing the risk of AMD.
In 1994, Dr Johanna Seddon and her co-workers at Harvard University reported a link between the intake of carotenoid-rich food, particularly dark green leafy vegetables like spinach, and a significant reduction in AMD (JAMA, Vol. 272, pp. 1413-1420).
Since then scores of studies have come out supporting the benefits, and elucidating the mechanisms involved.
New analysis
The new meta-analysis pooled data from only six longitudinal cohort studies. Crunching the numbers showed that the highest intakes of lutein and zeaxanthin were not associated with a reduced risk of early AMD.
On the other hand, the highest intake of these carotenoids was associated with 26% reduction in the risk of late AMD, and a significant reduction in the risk of neovascular AMD.
The researchers called for additional studies, particularly well-designed large studies, to provide “definitive conclusions” on the link between dietary lutein and zeaxanthin on AMD prevention.
Eye-opening market value
Lutein, a nutrient found in various foods including green leafy vegetables and egg yolk, has a ten-year history in the dietary supplement market as a nutrient to reduce the risk of age-related macular degeneration (AMD), the leading cause of blindness in the over 50s.
The US is by far the most developed market for eye health products, partly due to a greater acceptance of dietary supplements, and partly due to higher levels of awareness, according to data from Frost & Sullivan.
Frost & Sullivan placed the US eye health ingredients market at $138m in 2008, with a compound annual growth rate (CAGR) of 5.3 per cent from 2008 to 2015. The European market was valued at $43.4m in 2007 with a CAGR of 10.5 per cent from 2007 to 2014.
Source: British Journal of Nutrition
Published online ahead of print, FirstView Articles, doi: doi:10.1017/S0007114511004260
“Lutein and zeaxanthin intake and the risk of age-related macular degeneration: a systematic review and meta-analysis”
Authors: L. Ma, H-L. Dou, Y-Q. Wu, Y-M. Huang, Y-B. Huang, X-R. Xu, Z-Y. Zou, X-M. Lin