Health authorities worldwide recommend fatty fish and fish oil to reduce the risk of cardiovascular disease (CVD) and its adverse outcomes.
The adverse outcomes that omega-3-rich diets may help prevent include stroke and second heart attacks.
Omega-3s are most closely tied to prevention of “sudden cardiac death”, which is usually caused by arrhythmias (erratic heartbeat) and accounts for half of all heart-related deaths.
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Key Points
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Study links higher omega-3 levels to lower CRP (inflammation) levels.
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Findings affirm prior reports linking omega-3s to reduced inflammation.
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Not all studies find that omega-3-rich-diets lower inflammation, but most do.
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The established biological effects of omega-3s explain why they could reduce inflammation.
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In recent years, a new signal of risk for heart disease has emerged, called C-reactive protein or CRP.
Blood CRP levels rise when inflammation levels rise throughout the body. We still do not know whether CRP is simply a sign of cardiovascular disease, or if it actually plays a role in causing it.
The inflammation-heart link
Why would reducing inflammation levels help reduce the risk of heart attacks and other adverse heart events?
Inflammation promotes the buildup of arterial plaque, and it can cause the “cap” that encloses arterial plaques to rupture and release fatty clots into the bloodstream, causing a heart attack, ischemic stroke (the most common kind), or sudden cardiac death.
Annual physical exams include tests for blood levels of cholesterol and triglycerides, and most now include a test for CRP levels as well.
A newer test, called the high-sensitivity C-reactive protein (hs-CRP) assay, can more accurately determine a person’s risk for heart disease.
High CRP levels are now considered a major independent predictor for the risk of developing cardiovascular disease and suffering an adverse cardiovascular event.
U.S. and Japanese findings set the stage for Aussie report
Findings reported in the past five years from labs in Japan and the US have linked lower levels of omega-3s to higher levels of CRP (Lopez-Garcia E et al. 2004; Niu K et al. 2006; Murakami K et al. 2008).
Last year, researchers from the University of California San Francisco compared omega-3 and CRP levels in 992 people with coronary artery disease, as part of their “Heart and Soul Study”.
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What do CRP levels mean?
The American Heart Association provides these guidelines for the meaning of CRP levels (as found in hs-CRP blood tests), with regard to the risk of developing cardiovascular disease:
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CRP level lower than 1.0 mg/L = Low risk of developing cardiovascular disease.
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CRP levels between 1.0 and 3.0 mg/L = Average risk of developing cardiovascular disease.
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CRP levels higher than 3.0 mg/L = High risk for cardiovascular disease.
Of course, you should talk to your doctor about the meaning of your specific test results, because CRP levels are just one risk factor among several.
Among other things, inflammation can indicate the presence of infections, cancer, or autoimmune diseases such as lupus and rheumatoid arthritis.
And for reasons that remain unclear, CRP levels are sometimes low even in the presence of inflammation.
Nor is CRP the only marker of inflammation. Among other immune system chemicals, high levels of a protein called interleukin-6 (IL-6) also indicate systemic inflammation.
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After adjusting for various other risk factors, they linked higher omega-3 fatty acid levels (DHA+EPA) with lower levels of CRP and another major marker of inflammation, interleukin-6 (IL-6).
This association was not affected by the participants’ lifestyle factors, body-mass index, LDL-cholesterol levels, or their use of prescription statin drugs (e.g., Lipitor, Zocor), which exert strong anti-inflammatory effects.
As they wrote, “In patients with stable coronary artery disease, an independent and inverse association exists between omega-3 fatty acid levels and inflammatory biomarkers. These findings suggest that inhibition of systemic inflammation may be a mechanism by which omega-3 fatty acids prevent recurrent cardiovascular events.” (Farzaneh-Far R et al. 2008)
Aussie study affirms prior results
Last month, researchers from Australia's University of Newcastle reported finding a significant inverse relationship between blood levels of CRP and blood levels of DHA and EPA, the two key omega-3s in fish and fish oil (Micallef MA et al. 2009).
The study was led by Manohar Garg, Ph.D., who has co-authored more than 130 research papers concerning the interactions between dietary omega-3s and the body’s antioxidant and anti-inflammatory systems.
Professor Garg and his co-workers analyzed the blood levels of omega-3s and CRP in 124 participating adults (average age 47.7 years).
The participants were divided into three groups, based on their blood CRP levels: less than 1.0 mg/L, 1.0–3.0 mg/L, and more than 3.0 mg/L.
(See the sidebar titled “What do CRP levels mean?” to see the significance of these levels to a person’s relative risk of developing cardiovascular disease.)
People with CRP levels over 3.0 mg/l had significantly lower levels of total omega-3s and omega-3 EPA.
In other words, they found that people with higher omega-3 levels tended to have lower CRP levels, and vice versa.
And they proposed that these findings could help explain why omega-3s reduce the risk of heart disease: “… this inverse correlation [between omega-3 and CRP levels] … could represent a possible mechanism by which [omega-3] fatty acids are involved in CVD risk reduction.” (Micallef MA et al. 2009)
And they went on to make what seems like a logical observation: “Findings from this study support previous observations that omega-3 fatty acids may improve cardiovascular health in healthy individuals.” (Micallef MA et al. 2009)
Our reading of the mountains of prior evidence on that topic leaves us no choice but to agree!
Sources
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Farzaneh-Far R, Harris WS, Garg S, Na B, Whooley MA. Inverse association of erythrocyte n-3 fatty acid levels with inflammatory biomarkers in patients with stable coronary artery disease: The Heart and Soul Study. Atherosclerosis. 2008 Dec 14. [Epub ahead of print]
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Lopez-Garcia E, Schulze MB, Manson JE, Meigs JB, Albert CM, Rifai N, Willett WC, Hu FB. Consumption of (n-3) fatty acids is related to plasma biomarkers of inflammation and endothelial activation in women. J Nutr. 2004 Jul;134(7):1806-11.
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Madsen T, Schmidt EB, Christensen JH. The effect of n-3 fatty acids on C-reactive protein levels in patients with chronic renal failure. J Ren Nutr. 2007 Jul;17(4):258-63.
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Micallef MA, Munro IA, Garg ML. An inverse relationship between plasma n-3 fatty acids and C-reactive protein in healthy individuals. Eur J Clin Nutr. 2009 Apr 8. [Epub ahead of print] doi:10.1038/ejcn.2009.20
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Murakami K, Sasaki S, Takahashi Y, Uenishi K, Yamasaki M, Hayabuchi H, Goda T, Oka J, Baba K, Ohki K, Muramatsu K, Sugiyama Y. Total n-3 polyunsaturated fatty acid intake is inversely associated with serum C-reactive protein in young Japanese women. Nutr Res. 2008 May;28(5):309-14.
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Niu K, Hozawa A, Kuriyama S, Ohmori-Matsuda K, Shimazu T, Nakaya N, Fujita K, Tsuji I, Nagatomi R. Dietary long-chain n-3 fatty acids of marine origin and serum C-reactive protein concentrations are associated in a population with a diet rich in marine products. Am J Clin Nutr. 2006 Jul;84(1):223-9.
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