Written by Professor John Nolan, PhD - School of Health Science - Nutrition Research Centre Ireland
The quick answer is no, eating healthy is not sufficient on its own, and there are several reasons why! Of course we should eat healthy, and we know that fruits and vegetables contain compounds called carotenoids that have been identified in the eye and brain. Those carotenoids — lutein, zeaxanthin, and meso-zeaxanthin—have been shown to enhance vision and cognitive function through their antioxidant and anti-inflammatory properties [1,2]. We also know that patients with age-related macular degeneration (AMD) and Alzheimer’s disease have a deficiency in these nutrients .
Here’s how increasing carotenoids, referred to as macular pigment, in our diet can impact retina and brain health.
Importantly, carotenoids cannot be synthesized by humans and so they must be obtained from the diet, primarily through most fruits and vegetables and leafy greens. However, the average person (even the healthiest among us) in today’s society is not consuming sufficient amounts of the macular carotenoids in their standard diet. The average intake is roughly only 1.5mg daily, but studies have shown that we need to consume around 20mg daily to obtain maximal response. Of the three macular carotenoids—lutein, zeaxanthin, and meso-zeaxanthin—we consume significantly more lutein through our diet than we do zeaxanthin or meso-zeaxanthin; however, it is important to point out that all three are found in equal concentrations at the macula. This is likely due to the fact that a combination of the carotenoids exhibits the best antioxidant defense system for the macula [4-6], with meso-zeaxanthin as the most potent of them .
While the three carotenoids found in the macula have a similar chemical structure, they are different in the orientation of one hydroxyl group and the position of a double bond. This means that any one of the three macular carotenoids cannot be substituted for another. Approximately 12% of the population have central dips in their macular pigment (prevalent in people at risk of AMD) and are unable to convert lutein to meso-zeaxanthin at the macula; therefore, supplementing with all three carotenoids provides the only way to enrich macular pigment in these patients [7,8]. Finally, when meso-zeaxanthin is included in the formulation, improvements in visual function (notably contrast sensitivity) are significantly better than when this central carotenoid is absent [1,9,10].
In summary, supplementation with these targeted nutrients in combination with good nutrition and healthy lifestyles is required to support retinal/brain health and function for the growing and aging population. We now have the opportunity to utilize tested nutrition that is safe and effective to support eye and brain health.
1. Nolan JM, Power R, Stringham J, et al. Enrichment of macular pigment enhances contrast sensitivity in subjects free of retinal disease: central retinal enrichment supplementation trials - report 1. Invest Ophthalmol Vis Sci. 2016; 57(7):3429-3439.
2. Power R, Coen RF, Beatty S, et al. Supplemental retinal carotenoids enhance memory in healthy individuals with low levels of macular pigment in a randomized, double-blind, placebo-controlled clinical trial. J Alzheimers Dis. 2018;61(3):947-961.
3. Nolan J, Loskutova E, N Howard, A, et al. Macular pigment, visual function, and macular disease among subjects with Alzheimer's disease: an exploratory study. J Alzheimers Dis. 2014;42(4):1191-1201.
4. Li B, Ahmed F, Bernstein PS. Studies on the singlet oxygen scavenging mechanism of human macular pigment. Arch Biochem Biophys. 2010;504(1):56-60.
5. Meagher KA, Thurnham DI, Beatty S, et al. Serum response to supplemental macular carotenoids in subjects with and without age-related macular degeneration. Br J Nutr. 2013;110(2):289-300.
6. Thurnham DI, Nolan JM, Howard AN, Beatty S. Macular response to supplementation with differing xanthophyll formulations in subjects with and without age-related macular degeneration. Graefes Arch Clin Exp Ophthalmol. 2015;253(8):1231-1243.
7. Kirby ML, Beatty S, Loane E, et al. A central dip in the macular pigment spatial profile is associated with age and smoking. Invest Ophthalmol Vis Sci. 2010;51(12):6722-6728.
8. Nolan JM, Akkali MC, Loughman J, Howard AN, Beatty S. Macular carotenoid supplementation in subjects with atypical spatial profiles of macular pigment. Exp Eye Res. 2012;101:9-15.
9. Akuffo KO, Beatty S, Peto T, et al. The impact of supplemental antioxidants on visual function in nonadvanced age-related macular degeneration: a head-to-head randomized clinical trial. Invest Ophthalmol Vis Sci. 2017;58 (12):5347-5360.
10. Akuffo KO, Nolan JM, Howard AN, et al. Sustained supplementation and monitored response with differing carotenoid formulations in early age-related macular degeneration. Eye (Lond). 2015;29(7):902-912.