21 May 2019
Surely one of the most miraculous organs in the human body is the eye. It is so complex and delicate! The chief function of the eye is to collect light from the environment and turn it into an image that is transmitted to the brain. The lens of the eye is used to focus the image. The iris and pupil can adjust the amount of light coming into the eye. Muscles around the eye change the direction of vision. Light sensitive cells at the back of the eye take the image and convert it to signals the brain can read. The optic nerve carries the image to the brain. Other parts of the eye such as the vitreous humour and blood vessels support the eye by helping to hold its shape and nourishing it.
The eye requires a specialized set of nutrients to keep it functioning well now, and into the future.
Vitamin A is perhaps the most important nutrient for the eye. Vitamin A is used in the eye to convert light signals to the signals that are sent to the brain to form images. The hallmarks of vitamin A deficiency include problems with night vision and other eye concerns such as very dry eyes. The lack of vitamin A means that the body can no longer make the light-sensitive pigments needed to see in low-light situations. The eye membrane can also no longer produce tears to keep the surface of the eye moist when vitamin A intakes are too low. Permanent vision loss is a consequence of untreated vitamin A deficiency, so it is important to get enough!
Vitamin A can come from two sources. One is from meat, particularly organs such as the liver that contain retinol. This is called “pre-formed” vitamin A that is easiest for the body to take up. Bright orange, yellow or dark green leafy fruits and vegetables such as carrots and spinach contain beta-carotene, which is converted to retinol by a special enzyme in the small intestine. The amount vitamin A your body can make from beta-carotene depends on a lot of different factors such as whether the fruits and vegetables are cooked, and what you eat with them.
At the back of the eye we find the light-sensitive cells that receive the images that are sent to the brain, called the macula1. Curiously, two pigments from the food we eat collect right over where these cells are located. The two pigments are bright yellow, called lutein and zeaxanthin. Both are found in yellow, orange and dark green fruits and vegetables. It is thought that lutein and zeaxanthin may be able to protect the vision cells in the macula from damage from oxidation1.
Conditions such as age-related macular degeneration (AMD) may be related to lutein and zeaxanthin intakes. AMD is a significant cause of blindness, responsible for 9 percent of blindness globally and the major cause of blindness in developed countries2. It occurs when the vision cells at the back of the eye are damaged and lose their function over time. Due to their location, lutein and zeaxanthin may help prevent some damage to the vision cells in the macula that occurs over time1. Lutein and zeaxanthin supplements are prescribed as standard-of-care to people with a risk of developing age-related macular degeneration3.
Lutein and zeaxanthin can function as a light filter. Just as yellow filters are used in some situations to reduce glare from the sun or computer screens, lutein and zeaxanthin also block out some of the dazzling light that enters our eyes1. Higher levels of lutein and zeaxanthin in the eye are associated with better visual function4 and may help vision return more quickly after a strong flash of light5.
The omega-3 fatty acid docosahexaenoic acid (DHA) is found in high levels in the eye. It is required for normal visual development in infants6,7. In the eye, DHA makes up part of the walls of vision cells and influences their shape6,8. Infants who do not receive enough DHA are at risk of poor visual function. Human breast milk naturally contains DHA. When it is added to infant nutrition products, numerous clinical studies have shown that it can improve vision in infants9. It is now added routinely to infant nutrition products around the world.
Later in life, omega-3 fatty acids, particularly those from fatty fish, may also help with some eye complaints. Dry eye syndrome is a common eye concern especially for older people. In this condition, either the tear evaporation rate is greater than the tear production rate, leading to sore, dry eyes10. Prevalence rates vary between 5 to 35 percent in national surveys10. Researchers suggest that increased levels of omega-3 in the body can improve dry eye symptoms by reducing the inflammation associated with dry eye syndrome11. A meta-analysis found a significant decrease in dry eye syndrome across 17 clinical trials12.
We have identified several nutrients that are essential for eye health: vitamin A, macular pigments lutein and zeaxanthin, and omega-3 fatty acids. The best way to consume these nutrients is to follow national dietary guidelines that include advice to eat plenty of colourful fruits and vegetables and consume fatty fish at least once a week. Taking a dietary supplement can be considered when intakes do not meet these recommendations.
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15 December 2013
The beneficial effects of consuming omega-3 polyunsaturated fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on cardiovascular health have been studied extensively.
11 January 2012
Intake of high doses of B vitamins may improve mood and reduce psychological strain associated with chronic work stress, suggests a new Australian study.
15 February 2014
Up until this point, the methods of evidence-based medicine developed specifically for drugs (e.g., using randomized controlled trials) have been applied to nutrient research without apparent attention to important differences between drugs and nutrients.
