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Food, Health, and Eco-news
Omega-3s Seen as Stellar Bone-Builders
07/11/2005

High ratio of omega-3s to omega-6s called crucial to long-term bone health

by Craig Weatherby



For decades now, research findings have suggested that essential fatty acids—both omega-6s and omega-3s—play varying roles in maintaining bone health: specifically, bone density.


Now, two studies—one in humans, one in rodents—provide powerful support for the notion that omega-3 essential fatty acids (EFAs) are needed to build denser, more fracture-resistant bones. Just as importantly, the results of these studies indicate that the excess of dietary omega-6 fatty acids typical of the American diet cuts bone density and may increase the risk of fractures.


Omega-6 EFAs predominate in the most commonly used vegetable oils (soy, corn, canola, sunflower), and in most processed foods containing vegetable oils. And, as our readers know, fatty fish are the by far the richest sources of omega-3s, which are also found in nuts, seeds, and dark, leafy greens, albeit in much smaller amounts and in a much less usable form (alpha-linolenic acid).


Retirement community residents prove the point

In April of this year, researchers from the University of California's School of Medicine in San Diego reported the results of their investigating into the association between the ratio of dietary omega-6 to omega-3 fatty acids and bone mineral density (BMD). Their subjects were 1,532 men and women ranging in age from 45 to 90 who answered food intake questionnaires and underwent tests of their bone density.


They found that the hip bones of people who consumed more omega-6 EFAs relative to omega-3 EFAs were less dense—hence more prone to fracture—while people who consumed more omega-3 EFAs relative to omega-6 EFAs had denser, stronger bones.


As the authors said, “A higher ratio of n-6 [omega-6] to n-3 [omega-3] fatty acids is associated with lower BMD at the hip in both sexes. These findings suggest that the relative amounts of dietary polyunsaturated fatty acids may play a vital role in preserving skeletal integrity in older age.”


Rats ratify the results

In June of this year, researchers at Purdue University and the Indiana University School of Medicine published the results of their research into the effects on bone density of the ratio of omega-3 EFAs to omega-6 EFAs. Their subjects were sexually mature female rats.


First, they removed the ovaries of half the rats, to mimic the effects of menopause on bone health. As co-author Mark Seifert said, "Bone loss due to estrogen depletion in the adult female rat is very similar to that which occurs in post-menopausal women."


The researchers then divided the rats into two groups, each containing some of the ovariectomized rats. The two groups were fed diets containing different ratios of omega-6 to omega-3 EFAs.


Just as in the people participating in the University of California study, the rats that ate a diet higher in omega-6 EFAs suffered losses in bone mineral content and bone density, compared with rats that ate a diet higher in omega-3s.


This came as no surprise to the researchers. According to Bruce Watkins of Purdue University, '"Our lab and others have shown that omega-3 fatty acids help promote bone formation. We also have shown that higher intakes of omega-6 fatty acids lead to an increased production of compounds associated with bone loss."


Dr. Seifert noted that the anti-inflammatory effects of omega-3s could explain their bone benefits. Inflammation is mediated by messenger compounds (e.g., cytokines) that also promote the breakdown of bone.


The obvious conclusion is that you can help protect against fractures in later life by favoring foods high in omega-3s, and cutting back on processed foods and standard vegetable oils that are high in omega-6s. Better choices include olive, walnut, hemp, and macadamia nut oils.



Sources

  • Green KH, Wong SC, Weiler HA. The effect of dietary n-3 long-chain polyunsaturated fatty acids on femur mineral density and biomarkers of bone metabolism in healthy, diabetic and dietary-restricted growing rats. Prostaglandins Leukot Essent Fatty Acids. 2004 Aug;71(2):121-30.
  • Korotkova M, Ohlsson C, Hanson LA, Strandvik B. Dietary n-6:n-3 fatty acid ratio in the perinatal period affects bone parameters in adult female rats. Br J Nutr. 2004 Oct;92(4):643-8.
  • Sun L, Tamaki H, Ishimaru T, Teruya T, Ohta Y, Katsuyama N, Chinen I. Inhibition of osteoporosis due to restricted food intake by the fish oils DHA and EPA and perilla oil in the rat. Biosci Biotechnol Biochem. 2004 Dec;68(12):2613-5.
  • Watkins BA, Li Y, Seifert MF. Dietary ratio of n-6/n-3 PUFAs and docosahexaenoic acid: actions on bone mineral and serum biomarkers in ovariectomized rats. J Nutr Biochem. Article In Press, Uncorrected Proof, Available online 21 June 2005.
  • Weiss LA, Barrett-Connor E, von Muhlen D. Ratio of n-6 to n-3 fatty acids and bone mineral density in older adults: the Rancho Bernardo Study. Am J Clin Nutr. 2005 Apr;81(4):934-8.

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