Population study links higher omega-3 intake to 50% reduction in risk of macular degeneration
Yet another study has apppeared that affirms the potential for fish and fish-borne omega-3s to protect eye health.
Age-related macular degeneration (AMD) is a progressive eye condition in which the central part of the retina becomes damaged.
AMD is by far the leading cause of blindness and vision impairment. It causes central vision to darken and become blurry. AMD can lead to severe loss of vision and blindness.
As the condition develops from the early “dry” stage to the later “wet” stage—in which blood capillaries leak—retinal pigment cells become damaged and destroyed.
Omega-3s in eye function and health
The omega-3 fatty acid called DHA, found only in algae and fish, plays key functional and structural roles in all human cells, but is especially important to brain and eye function.
Practically speaking, the retina of the eye is a layer of brain tissue that receives energy from light, which it changes to biochemical and electrical signals to the brain, producing the mental phenomenon called “sight.”
The retina uses specialized photoreceptor cells called rods and cones to process light. Rod and cone cells are extraordinarily rich in DHA. A shortage of dietary DHA leads to a shortage of retinal DHA, which in turn reduces visual acuity.
But lack of dietary omega-3s—from fatty fish or fish oil supplements—can bring more ominous threats, like age-related macular degeneration.
Omega-3 DHA in the retina's cells is used to make a substance called neuroprotectin D1. This substance protects retinal pigment cells from damage and destruction. In addition, DHA itself helps protect the retina's pigment cells.
These twin protective actions help explain why people who eat fish more than once a week have significantly lower rates of AMD, according to the results of population studies.
For prior research on this topic, see “Fishy Help for Eye Health Affirmed by Aussie Analysis” and “Fish Seen Helping in Fight to Save Sight.”
New study affirms the role of omega-3s in eye health
Fish may help in more ways: Vitamin D and astaxanthin
Fatty fish may hold another agent key to eye health. In research we reported recently, vitamin D— which is uniquely abundant in wild Salmon—was found to exert complementary preventive impacts on AMD (Parekh N et al. 2007). See “Vitamin D Adds Eye Health to Roster of Recent Accolades.”
Omega-3s and vitamin D may indeed constitute the major eye-health constituents in fish, but wild Salmon are also rich in astaxanthin, which appears beneficial.
This highly potent antioxidant pigment exerts effects similar to those of its fellow xanthophyll-type carotenes—lutein and zeaxanthin— which are routinely prescribed by eye doctors because higher consumption of each compound is associated with reduced risk of AMD and cataracts (Parisi V et al. 2008; Bhosale P, Bernstein PS 2005).
The fish-vision connection has been strengthened by yet another population study linking higher omega-3 intake to reduced risk of age-related macular degeneration (AMD).
The findings show that eating one portion of omega-3-rich fish every week may halve the risk of developing the advanced, “wet” form of AMD (Augood C et al. 2008).
A team led by Astrid Fletcher of the LondonSchool of Hygiene & Tropical Medicine recruited 105 people aged 65 years with wet AMD, and 2,170 healthy people to act as controls.
They compared the participants' dietary habits using questionnaires. Only food sources of omega-3—not fish oil supplements—were considered.
People who reported eating at least one serving of fatty fish per week were 50 percent less likely to have wet AMD, compared to people who ate less than one fatty fish portion per week.
As expected, people whose reported diets contained at least an estimated 300 mg per day of either of the two key omega-3s in fish fat—DHA and EPA—were about 70 percent less likely to have wet AMD, compared to participants with lower estimated DHA or EPA consumptions.
(DHA is the key eye nutrient... EPA intake most likely served as marker for intake of DHA, since both omega-3s occur in fish, in roughly equal proportions.)
The study was funded by the European Commission, the Macular Disease Society UK, and the Thomas Pocklington Trust.
Clinical trials needed for confirmation
To date, there have been no randomized clinical trials (RCTs) testing the potential of omega-3s to reduce the risk of AMD.
While meta-analyses of population studies suggest that eating fatty fish twice or more per week—or taking fish oil regularly—may play an important role in the prevention of AMD, medical associations and public health authorities do not yet routinely recommend omega-3s and fish for this purpose.
This failure of medical authorities to act on the clear implications of ample epidemiological and laboratory evidence on the preventive potential of an essential human nutrient seems irresponsible.
Fish fit the vitamin D bill; Sockeye salmon stand out
Certain fish rank among the very few substantial food sources of vitamin D, far outranking milk and other D-fortified foods.
Among fish, wild Sockeye Salmon may be the richest source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent:
Vitamin D per 3.5 ounce serving*
- Sockeye Salmon 687 IU
- Albacore Tuna 544 IU
- Silver Salmon 430 IU
- King Salmon 236 IU
- Sardines 222 IU
- Sablefish 169 IU
- Halibut 162 IU
- Augood C, Chakravarthy U, Young I, Vioque J, de Jong PT, Bentham G, Rahu M, Seland J, Soubrane G, Tomazzoli L, Topouzis F, Vingerling JR, Fletcher AE. Oily fish consumption, dietary docosahexaenoic acid and eicosapentaenoic acid intakes, and associations with neovascular age-related macular degeneration. Am J Clin Nutr. 2008 Aug;88(2):398-406.
- Bhosale P, Bernstein PS. Microbial xanthophylls. Appl Microbiol Biotechnol. 2005 Sep;68(4):445-55. Epub 2005 Oct 26. Review.
- Leung IY. Macular pigment: new clinical methods of detection and the role of carotenoids in age-related macular degeneration. Optometry. 2008 May;79(5):266-72. Review.
- Parekh N, Chappell RJ, Millen AE, Albert DM, Mares JA. Association between vitamin D and age-related macular degeneration in the Third National Health and Nutrition Examination Survey, 1988 through 1994. Arch Ophthalmol. 2007 May;125(5):661-9.
- Parisi V, Tedeschi M, Gallinaro G, Varano M, Saviano S, Piermarocchi S; CARMIS Study Group. Carotenoids and antioxidants in age-related maculopathy italian study: multifocal electroretinogram modifications after 1 year. Ophthalmology. 2008 Feb;115(2):324-333.e2. Epub 2007 Aug 22.
- SanGiovanni JP, Chew EY, Clemons TE, Davis MD, Ferris FL 3rd, Gensler GR, Kurinij N, Lindblad AS, Milton RC, Seddon JM, Sperduto RD; 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, 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.
- Seddon JM, George S, Rosner B. Cigarette smoking, fish consumption, omega-3 fatty acid intake, and associations with age-related macular degeneration: the US Twin Study of Age-Related Macular Degeneration. Arch Ophthalmol. 2006 Jul;124(7):995-1001.
- Tan JS, Wang JJ, Flood V, Rochtchina E, Smith W, Mitchell P. Dietary antioxidants and the long-term incidence of age-related macular degeneration: the Blue Mountains Eye Study. Ophthalmology. 2008 Feb;115(2):334-41. Epub 2007 Jul 30.