Dr. Mark Roark Answers The Question — Do Western Dietary Deficiencies Affect Vision?
Too often, busy Americans fail to consider how their lifestyle choices — including the foods they eat and the supplements they take — may affect their ability to see. This begs the question: Is vision really affected by what I eat, so that my eyesight suffers if I live mainly on fast food and quick snacks?
Our last article dealt with the potentially devastating visual and overall health effects of vitamin A deficiency, something not common in the industrialized world. Yet, there are other unmet nutritional needs in developed countries that may affect both general health and visual function.
Shortfalls of the Western Diet
The USDA recommends a total of 4-5 cups of vegetables and fruits be consumed each day. This advice is backed by science showing that vegetables and fruits, when part of a healthy overall diet, can reduce the risk of chronic health problems like heart disease, type 2 diabetes, some cancers, and obesity. Yet, 90 percent of Americans fall short of these dietary recommendations and the most consumed vegetable among young children is french fries! (Figure 1)
Unhealthy lifestyle choices that include empty calories from sweetened beverages and fast foods, smoking, and lack of exercise have led to 70 percent of Americans being overweight — with an obesity rate of 40 percent. This problem also affects our youth with an obesity prevalence of 20 percent in children and adolescents. (Figure 2) In addition, poor dietary habits have deprived us of the nutrients necessary for optimal vision.
Figure 1. Males and females of every age are falling short of recommended dietary fruit and vegetable intake. (ODPHP)
Benefits of Colorful Carotenoids
What are these missing components of a healthy diet? As we ingest dark, leafy greens along with colorful fruits and vegetables, our bodies are supplied with important nutrients including carotenoids. These healthful pigments are found throughout the natural world and are responsible for many of the beautiful colors in the plant and animal kingdoms. Because carotenoids are essential to eye and body health and humans cannot make them, they must be obtained through the diet.
Looking at the diagram, (Figure 3) we see the macula is a unique part of the retina that lines the back inner surface of the eye. It is centrally positioned to receive focused light and is packed with millions of rods and cones that serve as light receptors for vision. It is critical for this part of the eye to remain healthy throughout life since it gives us the ability to see faces and fine details.
When supplied with the proper carotenoids from the diet, the human body has the amazing ability to form a band of yellow pigment directly in front of the macula. This protective shield, known as the Macular Pigment (MP), is composed of three unique carotenoids: lutein (L), zeaxanthin (Z), and meso-zeaxanthin (MZ). These work as a team to protect the macula from blue light damage and oxidative stress, especially important since the macula maintains the highest metabolic rate in the entire body!
Optimizing Vision by Increasing Macular Carotenoids
These three carotenoids also have another essential function that is not well known. When an optimal amount of MP is present, vision is optimized in at least two ways:
MP reduces visual glare by absorbing blue light that is otherwise scattered within the eye. Although there can be other factors, many patients suffer needlessly from light sensitivity and annoying glare simply because they lack sufficient macular carotenoids.
MP improves contrast sensitivity (CS), a visual skill needed to detect the edges in a scene and to discriminate a target from its background. The nerve tissue that connects the eye to the brain needs MP to boost the electrical signal and enhance CS. Patients with poor contrast sensitivity are more likely to struggle in situations like driving at night or in the fog.
How much L, Z, and MZ do we need to obtain these visual benefits? Based on research, an optimal daily amount would be 12-24 mg per day though much higher doses are safe. The average American diet, however, contains only 1.5 mg per day, which is not enough to provide optimal vision. A change in dietary habits is needed but can be challenging for many.
Science Confirms the Benefit
Taking a supplement to increase L, Z, and MZ could also be of benefit, but many consumers are understandably confused when trying to choose between various products. Fortunately, high-quality supplements with L, Z, and MZ are available and excellent research indicates they improve vision. For instance, a landmark study known as CREST Normal studied the effects of a triple carotenoid supplement for a year in healthy adults with no eye disease. Results demonstrated significant improvements in contrast sensitivity compared to placebo.
The bottom line? A healthy lifestyle that includes proper dietary choices and carefully selected supplements can have a positive impact on visual performance for patients of all ages.
Our final blog in this series will explore ways in which nutrition can reduce risk for developing the number one cause of central blindness among those age 55 and above: Age-related Macular Degeneration (AMD). This disease now affects 1 in 3 Americans above the age of 75 and is projected to increase substantially with the aging of the population, so this topic is worthy of our attention.
About Dr. Roark
Dr. Roark graduated from Indiana University with a Doctorate in Optometry and founded Allisonville Eye Care Center in Fishers, Indiana. Dr. Roark specializes in the scientific field of visual performance and ocular nutrition, and has lectured frequently to other Eye Care Professionals, both nationally and internationally. He recently co-authored a peer-reviewed article published in a special edition of the Molecular Nutrition and Food Research journal on “Nutrition for the Eye and Brain.”