Findings affirm earlier indications that omega-3s from plants or fish reduce bone loss
by Craig Weatherby
According to the International Osteoporosis Foundation, the direct cost to America of osteoporotic fractures totaled a staggering $17.5 billion in 2002. And of course, the indirect toll from health declines due to hip fractures is far higher, in terms of both dollars and despair.
This is why recent findings on vitamin D’s underestimated importance to bone health were so important, and these grim statistics make today’s news well worth spreading.
It’s been known for some time that omega-3s play a role in bone health, via beneficial effects on calcium uptake and retention.
For example, here’s what the authors of a recent animal study (Kruger MC, Schollum LM 2005) reported:
- “Calcium absorption … bone mineral density, and bone calcium content were significantly higher in the animals fed tuna oil compared with those of a control group fed corn oil.
- “Significant correlations were found between the … [omega- DHA] … content of the red cell membranes and bone density and bone calcium content. DHA increased accretion of calcium in bone significantly more so than … EPA ...”
Earlier investigations indicated that diets with low ratios of omega-6 fatty acids to omega-3 fatty acids could minimize bone loss, but most of the studies focused on EPA and DHA: the long-chain omega-3 fatty acids from fish.
And until this month, no one had published a study conducted in humans.
Dr. Amy Griel of Penn State University led a team that sought to redress this yawning gap in our understanding of how foods affect bone health, and they published very encouraging results earlier this month (Griel AE et al 2007).
Instead of fish or fish oil, they gave some of the subjects sources of alpha-linolenic acid (ALA): the short-chain omega-3 found in plants, which humans convert into the two long-chain omega-3s found in fish and in human cell membranes (EPA and DHA).
They recruited 23 people for randomized, three-period crossover trial, and assigned them to eat one of three diets for six weeks:
- Average American Diet: 34 percent total fat, 13 percent saturated fatty acids (SFA), 13 percent monounsaturated fatty acids (MUFA), 9 percent polyunsaturated fatty acids UFA (7.7 percent omega-6, 0.8 percent omega-3 ALA)
- Omega-6-Rich Diet: 37 percent total fat, 9 percent SFA, 12 percent MUFA, 16 percent PUFA (12.6 percent omega-6 LA, 3.6 percent omega-3 ALA)
- Omega-3-Rich Diet: 38 percent total fat, 8 percent SFA, 12 percent MUFA, 17 percent PUFA (10.5 percent omega-6 LA, 6.5 percent omega-3 ALA).
Walnuts and flaxseed oil were the main sources of omega-3 ALA in the subjects’ diets. (While not as abundant in them, dark, leafy greens are significant sources of short-chain omega-3s.)
The Penn State team set out to measure the effect of omega-3s on bone turnover (more is better), as determined by blood levels of two key markers of, respectively, bone resorption and bone formation: N-telopeptides (NTx) and bone-specific alkaline phosphatase (BSAP).
(Resorption is the metabolic process that results in loss of calcium and weakened bones: it exists in balance with bone formation, so excessively high levels of NTx are a sign that bone resorption is outpacing bone formation.)
Higher blood levels of NTx are also associated with higher levels of inflammation, and inflammation is known to promote bone loss.
Study finds plant-derived omega-3s good for bones
At the end of the study, the people on the omega-3-rich-diet (diet number three) had the lowest levels of NTx and inflammation. There was no difference among the three diets in terms of the blood levels of BSAP.
As the authors said, “The results indicate that plant sources of dietary … [omega-3s] … may have a protective effect on bone metabolism via a decrease in bone resorption in the presence of consistent levels of bone formation.” (Griel AE et al 2007)
The positive results of this small study lend weight to the idea that we can add bone health to the growing list of benefits that omega-3s bring.
- Griel AE, Kris-Etherton PM, Hilpert KF, Zhao G, West SG, Corwin RL. An increase in dietary n-3 fatty acids decreases a marker of bone resorption in humans. Nutr J. 2007 Jan 16;6(1):2 [Epub ahead of print]
- Shen CL, Yeh JK, Rasty J, Li Y, Watkins BA. Protective effect of dietary long-chain n-3 polyunsaturated fatty acids on bone loss in gonad-intact middle-aged male rats. Br J Nutr. 2006 Mar;95(3):462-8.
- Mollard RC, Weiler HA. Dietary arachidonic acid and docosahexaenoic acid elevate femur calcium and reduce zinc content in piglets. Pediatr Res. 2006 Oct;60(4):418-22. Epub 2006 Aug 28.
- Cohen SL, Ward WE. Flaxseed oil and bone development in growing male and female mice. J Toxicol Environ Health A. 2005 Nov 12;68(21):1861-70.
- Kruger MC, Schollum LM. Is docosahexaenoic acid more effective than eicosapentaenoic acid for increasing calcium bioavailability? Prostaglandins Leukot Essent Fatty Acids. 2005 Nov;73(5):327-34.