Last Updated: Friday, July 10, 2009 | 4:26 PM ET
By Michelle Gelok, CBC News Science continues to show us that certain nutrients are needed by different areas of the body to boost health and prevent disease. Whether it's the omega-3 fatty acids in fish that boost heart health or the calcium in milk that keeps bones strong, there's no denying the role that food plays in the prevention of disease.
Often overlooked, however, is the role that food plays in keeping our eyes in top form.
Recent research findings published in May in Ophthalmology, the journal of the American Academy of Ophthalmology, are shedding light on the link between diet and eye health.
The study, conducted by researchers at Tufts University in Massachusetts, is the first of its kind to look at the combined effect of nutrients on eye health, and to examine their role in the prevention of age-related macular degeneration (AMD), a leading cause of blindness in adults. Researchers analyzed data from more than 4,000 participants and assessed their intake of nutrients including vitamins C and E, zinc, lutein, zeaxanthin, omega-3 fatty acids and low-glycemic-index foods.
Age-related macular degeneration or AMD.
AMD affects the macula, located in the centre of the retina, which is the part of the eye that allows you to see fine details.
According to the Canadian National Institute for the Blind, more than one million Canadians have AMD.
Each dietary factor was assigned a score, and the scores were totalled and compared to the AMD risk for participants. Researchers found that higher scores were associated with a lower risk of developing AMD. In other words, the higher the intake of protective nutrients, the less likely the participants were to develop AMD.
While these findings are the first to measure the combined effect of protective nutrients, it turns out researchers have been studying each of these nutrients in isolation for years. Here's a rundown of the top nutrients, and their food sources, that have been shown to help keep eyes healthy.
Omega-3s
Omega-3 fatty acids, most popular for their heart health benefits and anti-inflammatory properties, are beginning to make their mark when it comes to keeping our peepers in top form.
A major study published last year in the Archives of Ophthalmology reviewed data from nine studies with a total of more than 88,000 participants. It found that a high intake of omega-3 fatty acids was associated with a 38 per cent reduction in the risk of AMD. Researchers also found that eating fish at least twice a week was associated with a decreased risk of AMD.
The best sources of omega-3 fatty acids include fatty fish such as salmon, mackerel and herring, as well as ground flax seeds, walnuts and soybeans.
Lutein and zeaxanthin
Lutein and zeaxanthin, though they may sound like a tongue twister when said together, are two yellow pigments that get top marks for their link to eye health.
Lutein and zeaxanthin are compounds found in the retina of the eye, as well as some foods. They are actually antioxidants that have been shown to offer protection from both AMD and cataracts by protecting against oxidation of healthy tissue in the eye. One study published in the Archives of Ophthalmology in 2007 found an inverse relationship between the dietary intake of lutein and zeaxanthin and risk for developing AMD. In other words, participants with higher intakes of lutein and zeaxanthin experienced an overall decreased risk of AMD.
Though they are yellow pigments, these two compounds are found in a variety of colourful produce, including spinach, kale, squash, green peas, broccoli and corn.
Vitamin A
Carrots, perhaps the most well known food when it comes to eye health, have long been linked to eyesight - and for good reason. Carrots are an excellent source of beta-carotene, a nutrient converted into vitamin A in the body.
While the study mentioned earlier didn't find a link between vitamin A intake and decreased risk of AMD, one of vitamin A's roles in the body is to help the retina function properly, and this is essential for general eye health. According to the World Health Organization, vitamin A deficiency is the leading cause of preventable blindness in children. A deficiency of this fat-soluble vitamin is also linked to night blindness in adults.
The best dietary source of beta-carotene and vitamin A include organ meats, orange root vegetables (such as carrots), and green leafy vegetables.
Vitamin C
While vitamin C is best known for its ability to help fight off the common cold, it turns out it plays a role in preventing AMD and related vision loss as well.
When combined with vitamin E, beta-carotene and zinc in high doses, vitamin C was found to lower the risk of AMD by 25 per cent in people at high risk for the disease. The clinical trial, called the Age-Related Eye Disease Study (AREDS), which was published in the Archives of Ophthalmology in 2001, also found that this high-dose combination of vitamins and minerals reduced the risk of vision loss caused by AMD by 19 per cent.
Another study, conducted on animals and published in the journal Microvascular Research in 2007 found that long-term vitamin C supplementation might play a role in preventing diabetic retinopathy — a leading cause of blindness in diabetics.
While both studies used vitamin C supplements, until conclusive dosage recommendations are made it's best to stick to food sources to get the amount you need to keep your eyes healthy. Excellent dietary sources of vitamin C include papaya, red bell peppers, kiwi, strawberries and oranges.
Low glycemic index foods
A study published last year in the American Journal of Clinical Nutrition found that the glycemic index (GI), a measure of how quickly carbohydrates raise blood glucose levels, also affected the risk for AMD. Researchers found that a diet rich in high GI foods, those that cause a rapid rise and fall in blood glucose levels, was associated with a greater risk and increased severity of AMD.
The findings aren't entirely surprising, since low GI foods have already been linked to a decreased risk of heart disease and Type 2 diabetes.
High GI foods tend to be highly processed refined foods, such as white bread, French fries and potatoes, whereas low GI foods are higher in fibre, including oat bran, lentils, beans and barley.
The author is a Canadian licensed registered dietitian.EARN HEALTH & WEALTH
