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TalkingNutrition

Providing perspectives on recent research into vitamins and nutritionals

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Seeing the Present as it is: Omega-3 Index of Americans

By Michael McBurney

Everybody wants to grow old with grace.  The fear of losing our vision, not being able to see at night, not being able to read is frightening. Sometimes, despite our efforts, genetics play an important role in disease processes. Such is the case with retinitis pigmentosa, a degenerative retinal disease that affects approximately 1 person in 100,000.

The retina of the eye is enriched with docosahexaenoic acid (DHA), a polyunsaturated omega-3 fatty acid and the antioxidant vitamin E. Within the central part of the retina, the fovea, two antioxidant carotenoids (lutein and zeaxanthin) are concentrated and deposited. These nutrients help maintain normal vision.

Based on previous findings that 1-2 years of DHA supplementation benefitted children and adults with hereditary retinal disease, Hoffman and colleagues conducted an intervention trial to determine the effect DHA supplementation (30 mg/kg/d for 4 years) on disease progression in 33 participants (mean age of 15-16 years) with hereditary retinitis pigmentosa (versus 27 with the disease randomized to placebo).  Baseline red blood cell (RBC) DHA concentrations were 2.86% (ranging from 1.8-3.8) in the placebo group and 3.12% (ranging 1.8-6.3) in those assigned to treatment.  In the intervention group, DHA intake during the study ranged from 600 to 3,600 mg/d. DHA supplementation increased RBC DHA 3.3-fold (10.1%) but supplementation did not statistically affect disease progression [measured as rate of change in cone electroretinography (ERG) amplitude].  Why?

There could be many reasons. For unknown reasons, these individuals had unusually low disease progression rates (4.9 to 6.2% annually).  Previous studies observed annual declines in cone ERG of  14-18% (Birch et al, 1999; Hoffman et al, 2004). The authors could only speculate on the low rates of progression in this small cohort.

Better overall nutrition might be an explanation. Participants were asked to take 3 to 18 capsules daily. Each capsule contained 12.5 mg vitamin C and 12.5 mg vitamin E (37.5-225 mg/d). These vitamins were added to protect the fatty acids from becoming rancid (oxidation) and to keep the intervention balanced in the placebo group. In addition, everyone was given a multivitamin with 100% of the RDA for vitamins A, C, D, E, B6, and B12. This would be above and beyond the vitamins consumed from their diet. To summarize, the volunteers had better than average vitamin intakes. According to What We Eat in America, NHANES 2009-2010, the average 12-19 year old is under consuming vitamin A (70-75% of RDA), vitamin D (31-42%), and vitamin E (43-52% of RDA).

Finally, genetically inherited retinitis pigmentosa may not be amenable to DHA supplementation. Clearly, DHA supplementation increased RBC DHA concentrations. At 30mg/kd/d, RBC DHA percentages were similar to those measured in humans with a high omega-3 index (9.8% DHA). Baseline RBC DHA percentages were less than average (4.82 %, which is comparable to that in dolphins). One thing is for certain, the data from Hoffman and colleagues confirms that the omega-3 index of most people in America  trends below 4%. The is less than half of the average omega-3 index (9-10%) measured in Japanese populations.

There are health benefits to consuming more omega-3 fatty acids, especially DHA and its precursor eicosapentaenoic acid (EPA). To learn more about people’s views on their diets, willingness to improve them, and general beliefs about diet and exercise, register for the  International Food Information Council (IFIC) Foundation webcast presenting the 2014 Food & Health Survey: The Pulse of Americans’ Diet from Beliefs to Behaviors on May 20, 2014.


Main Citation

Hoffman DR, Hughbanks-Wheaton DK, Pearson NS, Fish GE, Spencer R, Takacs A, Klein M, Locke KG, Birch DG. Four-year placebo-controlled trial of docosahexaenoic acid in X-linked retinitis pigmentosa (DHAX Trial): A randomized clinical trial. 2014 JAMA Opthalmol doi: 10.1001/jamaopthalmol.2014.1634

Other Citations

Gillingham MB, Weleber RG, Neuringer M, Connor WE, Mills M, van Calcar S, ver Hoeve J, Wolff J, Harding CO. Effect of optimal dietary therapy upon visual function in children with long-chain 3-hydroxyacyl CoA dehydrogenase and trifunctional protein deficiency. 2005 Mol Genet Metab doi: 10.1016/j.ymgme.2005.06.001

Lee TK, Clandinin MT, Hebert M, MacDonald IM. Effect of docosahexaenoic acid supplementation on the macular function of patients with Best vitelliform macular dystrophy: randomized clinical trial. 2010 Can J Opthalmol doi: 10.3129/i10-028

Birch DG, Anderson JL, Fish GE. Yearly rates of rod and cone functional loss in retinitis pigmentosa and cone-rod dystrophy. 1999 Opthalmol doi: 10.1016/S0161-6420(99)90064-7

Hoffman DR, Locke KG, Wheaton DH, Fish GE, Spencer R, Birch DG. A randomized, placebo-controlled clinical trial of docosahexaenoic acid supplementation for X-linked retinitis pigmentosa. 2004 Am J Opthalmol doi: 10.1016/j.ajo.2003.10.045

Harris WS, Schmitt TL. Unexpected similarity in RBC DHA and AA levels among bottlenose dolphins and humans. 2014 PLEFA doi: 10.1016/j.plefa.2013.12.005


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