Americans’ low omega-3 intake and excessive omega-6 consumption promote a common, potentially blinding condition
by Craig Weatherby
Last week, researchers reported that diets rich in fish-borne omega-3s may reduce the risk of age-related macular degeneration (AMD) by about 40 percent.
At the same time, high intake of the omega-6 fatty acids vastly overabundant in American diets were associated with increased risk of AMD.
These findings highlight the dangers of the woefully imbalanced American diet, which is much too low in omega-3s and much too high in omega-6s: the two families of dietary fatty acids whose previously overlooked interactions and health effects have finally become the focus of extensive research.
The results come from a study involving 4,519 older people, which found a strong association between fish-rich diets and lower risk of AMD.
(Note: In a companion study, the vitamin D abundant in wild salmon was found to exert complementary preventive impacts on AMD. See “Vitamin D Adds Eye Health to Roster of Recent Accolades,” in this issue of "Vital Choices.")
AMD is the leading cause of blindness in Americans aged 55 and older, and of the 30,000,000 people over age 65 in the US in 1990, almost one in three show evidence of the eye disease. The number of Americans over age 65 will double by the year 2030, so researchers have sought to reveal any foods that might help prevent the vision-crippling condition.
AMD comes in two forms: early or “dry” stages, and subsequent “wet” stages. The wet forms are named for the under-retina overgrowth of blood vessels that characterize this type of AMD. Although it afflicts less than 10 percent of patients, wet AMD causes 85 percent of severe AMD-related vision loss.
The majority of wet AMD cases get little help from the leading therapy, called laser photocoagulation. But in recent years, this procedure’s efficacy has been greatly enhanced by injecting patients with a drug called verteporfin before the laser treatment is applied (While results vary, this writer’s 70-something stepmother underwent the drug-laser AMD treatment recently, with very substantial success).
Research results reported in recent years—especially those from Australia’s “Blue Mountains” eye study—indicate that omega-3s from fish may help prevent AMD. And other research findings suggest that omega-s can also help prevent or improve dry eye syndrome, cataracts, and lens opacities (See “Fish Seen Helping in Fight to Save Sight” in the July 18, 2006 issue of Vital Choices, which contains links to several Vital Choices articles on this subject).
The new findings support the AMD-preventive potential of inflammation-moderating omega-3s, and they also extend to eyes the health risks associated with the excessive intake of inflammation-fueling omega-6 fatty acids characteristic of the average American’s diet.
Omega-6 fatty acids compete with omega-3s for space in the membranes of eye cells (and all body cells). Excessive dietary intake of omega-6s is known to promote cancer growth, and it now appears that Americans’ typical omega-6 overload may be a threat to aging eyes as well, probably because of their pro-inflammatory effects.
Omega-6s abound in standard, grain-fed meats and poultry and they predominate in the vegetable oils used most commonly for home cooking and in packaged and restaurant foods (corn, safflower, soy, canola, sunflower, and cottonseed).
Let’s take a closer look at the enlightening details of the new study.
Americans’ low omega-3/omega-6 diet ratio poses long-term vision risks
The new findings flow from analysis of data from the Age-Related Eye Disease Study (AREDS), conducted under the auspices of the National Eye Institute (NEI).
AREDS involved researchers at universities and clinics in nine states, who enrolled 4,757 subjects, surveyed the participants about their diets and lifestyles, and gave them detailed eye exams.
Red antioxidant pigment makes salmon the best fish for eye health
Until recently, the leading contenders in the battle to prevent AMD were two xanthophyll-class antioxidants called lutein (loo-teen) and zeaxanthin (zee-ah-zan-thin).
This pair occurs in the retina of human eyes as well as in broccoli, corn, spinach, kale, chard, and certain other yellow-green vegetables.
But the pigment that makes salmon red—astaxanthin—is also a xanthophyll-class antioxidant. And the results of animal studies show that astaxanthin, like lutein and zeaxanthin, neutralizes free radicals in the eyes, thereby preventing oxidative damage stemming from UV sunrays.
Astaxanthin also moderates the body's potentially counterproductive inflammatory response to UV-induced damage to eye cells.
The new AREDS data analysis adds significant support to prior indications that omega-3s protect against AMD, and that excessive intake of omega-6 fatty acids promotes increased risk of AMD (Seddon JM, Cote J, Rosner B 2003).
The AREDS research group took photographs of 4,519 subjects’ retinas to determine the precise nature and extent of any AMD detected. The participants were between 60 and 80 years old at the start of the study, and their food intake was assessed with a standard questionnaire.
At the outset, about one in four of the subjects was free of AMD symptoms. They were compared with those who had AMD symptoms, including 658 people with well-advanced (wet) AMD.
The authors found that higher intake of omega-3 fatty acids from fish cut the risk of wet AMD by 39 percent, with one fish-borne omega-3 in particular (DHA) associated with a 46 percent reduction.
And the people who were the least likely to have AMD where those who either ate more than two medium (4 oz / 113 gram) servings of fish per week, or more than one serving of broiled or baked (not fried) fish.
It is significant that it took fewer weekly servings of non-fried fish to be protective, versus fish in general... a category that, for the average American, includes lots of fried fish sticks and “fishwiches”. This difference can be plausibly attributed to the unhealthful amount of omega-6-rich vegetable oil left in their bread coatings.
The researchers hypothesized that marine omega-3s may protect the retina by promoting activation of genes that slow or stop the overgrowth of blood vessels in wet AMD and by forming messenger chemicals (e.g., prostaglandins) that reduce inflammation and aid blood vessel function.
In contrast, high dietary intake of omega-6 AA (arachidonic acid) was associated with a 54 percent increase in wet AMD. Arachidonic acid is a generally pro-inflammatory fatty acid, which, like omega-3 DHA, is essential to cell membrane structure and function. Arachidonic acid is concentrated in grain-fed meats and poultry, and the body converts a large proportion of the omega-6 fatty acid in vegetable oils (linoleic acid) into AA.
As the researchers said, “Because increased intake of [omega-6] AA is also associated with an increased likelihood of having NV [wet] AMD, it is important to consider the balance and composition of dietary long chain polyunsaturated fatty acids from the omega-3 and omega-6 families.”
- [Age-Related Eye Disease Study Research Group]. The Relationship of Dietary Lipid Intake and Age-Related Macular Degeneration in a Case-Control Study: AREDS Report No. 20. Arch Ophthalmol 2007 May;125(5):671-9.
- Seddon JM, Ajani UA, Sperduto RD, Hiller R, Blair N, Burton TC, Farber MD, Gragoudas ES, Haller J, Miller DT, et al. Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration. Eye Disease Case-Control Study Group. JAMA. 1994 Nov 9;272(18):1413-20. Erratum in: JAMA 1995 Feb 22;273(8):622.
- Seddon JM, Gensler G, Milton RC, Klein ML, Rifai N. Association between C-reactive protein and age-related macular degeneration. JAMA. 2004 Feb 11;291(6):704-10.
- Seddon JM, Cote J, Rosner B. Progression of age-related macular degeneration: association with dietary fat, transunsaturated fat, nuts, and fish intake. Arch Ophthalmol. 2003 Dec;121(12):1728-37. Erratum in: Arch Ophthalmol. 2004 Mar;122(3):426.
- Age-Related Eye Disease Study (AREDS). Accessed online May 17, 2007 at http://www.nei.nih.gov/neitrials/static/study44.asp