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Do Fishy Diets Drive Japan’s Superior Heart Health?
Large study links fish-rich diets to the Asian nation's low heart disease levels
3/6/2014By Craig Weatherby
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Everyone’s heard that fish and their omega-3 fatty acids (EPA and DHA) are good for heart health.
 
That impression flows primarily from four large studies in Britain, Italy, and Japan. For the details, see our sidebar, “Why do doctors recommend fish oil?”.
 
Those findings have not been persuasively undermined by any of the studies claimed to question the heart-health value of fish and fish oil, which all suffered from serious flaws.
 
Now, another study focused on Japan adds even more evidence that fish is a major heart-health ally.
 
The Japanese paradox
Among developed countries, Japan enjoys very low rates of heart disease.
 
In fact, death rates from coronary heart disease in Japan have been less than half the rate in the U.S.
 
This holds true even among Japanese men born after World War II who adopted a Western lifestyle since childhood.
 
Why do doctors recommend fish oil?
The answer lies in mountains of lab, animal, epidemiological, and clinical evidence … but rests most heavily on four large human studies.
 
The DART Study followed 2,033 British men who’d suffered a heart attack for two years. The results showed that higher intakes of fatty fish reduced the risk of death from any cause by 29 percent, and prompted recommendations that everybody should consume two servings of fatty fish per week.
 
Italy’s GISSI-Prevenzione clinical trial tested the effects of omega-3 fish oil in 8,488 recent heart attack survivors, and showed that taking one gram of EPA + DHA per day for 3.5 years reduced the risk of death from any cause by 14 to 20 percent, and the risk of heart-related death by between 17 to 30 percent.
 
(A follow-up to the GISSI-Prevenzione trial also found that EPA and DHA were more cost effective than some statins at reducing all-cause deaths following the initial heart attack.)
 
The GISSI-HF trial involved 6,975 Italian heart failure patients placed on traditional treatment for heart failure, and showed that taking one gram of EPA + DHA per day for up to 4.5 years reduced the risk of death from any cause by an average of nine percent, the risk of heart-related death or hospitalization by eight percent.
 
Finally, the JELIS study followed 18,645 Japanese patients being treated with statins for high cholesterol for five years and showed that taking 1.8 grams of omega-3 EPA per day reduced the risk of major coronary events by 19 percent, versus statin therapy alone.
 
Japan’s JELIS study also found that EPA reduced the risk of a secondary major coronary event by 27 percent, the risk of heart attack by 23 percent, and the risk of a first heart attack by 53 percent among patients with high triglyceride and low HDL cholesterol levels.
 
Omega-3 EPA supplements also substantially reduced the risk of unstable angina, non-fatal coronary events (e.g., heart attacks) and stroke.
And the Japanese advantage holds true despite the fact that their risk factors for coronary heart disease are very similar to American men.
 
These include similar cholesterol levels, blood pressure, and rates of type 2 diabetes among Japanese men … plus much higher rates of cigarette smoking and work-related stress, compared with American men.
 
But while the average American eats fish less than two times a week, Japan has one of the highest fish intakes in the world … an average of 100 grams (3.5 ounces) daily.
 
Prior study linked high omega-3s to healthier arteries 
Six years ago, a study led by researchers from the University of Pittsburgh examined Japanese, white American, and Japanese-American men (Sekikawa A, et al. 2008).
 
Study researchers in both countries compared the rates of atherosclerosis (hardening/narrowing or arteries) to blood levels of omega-3 fatty acids among 868 Japanese, white American, and Japanese-American men between the ages of 40 and 49.
 
Their analysis showed that the Japanese men had lower levels of atherosclerosis and higher levels of omega-3 fatty acids, compared with the white American and Japanese American men.
 
Importantly, levels of atherosclerosis among third- and fourth-generation Japanese-American men were similar to or even higher, compared to white Americans.
 
The differences in the levels of atherosclerosis between Japanese and white Americans remained after adjusting for other risk factors – cholesterol levels, blood pressure, cigarette smoking, body mass index, and diabetes.
 
“Our study suggests that very high levels of omega-3 fatty acids have strong properties that may help prevent the buildup of cholesterol in the arteries,” said Akira Sekikawa, M.D., Ph.D., study lead author and assistant professor of epidemiology at the University of Pittsburgh Graduate School of Public Health (UP 2008).
 
As he said, “Our study shows much higher intake of fish observed in the Japanese may have strong anti-atherogenic effect.” (UP 2008)
 
“The Japanese eat a very high level of fish compared to other developed countries,” said Dr. Sekikawa. “Given the similar levels of atherosclerosis in Japanese Americans and white Americans, it also tells us that lower levels of heart disease among Japanese men are much more likely lifestyle related than a result of genetic differences.” (UP 2008)
 
The Japanese men had lower levels of atherosclerosis (hardening/narrowing or arteries) and higher levels of omega-3 fatty acids, compared with the white American and Japanese American men.
 
Importantly, levels of atherosclerosis among third- and fourth-generation Japanese-American men were similar to or even higher, compared to white Americans.
 
The differences in the levels of atherosclerosis between Japanese and white Americans remained after adjusting for other risk factors – cholesterol levels, blood pressure, cigarette smoking, body mass index, and diabetes.
 
Now, the results of a follow-up study strengthen the idea that the fish-consumption gap between the U.S. and Japan accounts for an otherwise inexplicable paradox.
 
Fishy diets linked to low heart disease levels in Japanese men
Like the 2008 study, the follow-up study was led by researchers from the University of Pittsburgh (Sekikawa A, et al. 2013).
 
This time, they sought to determine whether blood levels of omega-3s might account for known differences in the rate of coronary artery calcification (CAC) – a major heart-risk factor – between Japanese men and white American men. The study involved 175 Japanese men and 113 white men aged 40–49 years.
 
And the results showed two key things:
  1. Omega-3 levels were twice as high in the Japanese men.
  2. Japanese men had a significantly lower rate of CAC compared to white men.
Significantly, the Japanese advantage in rates of CAC remained significant after adjusting for age, blood pressure, LDL cholesterol, diabetes, and other risk factors.
 
As the authors conduced, “Omega-3 blood levels significantly contributed to the difference in the incidence of CAC between Japanese and white men.”
 
Omega-3 levels are highest in oily fish such as salmon, tuna, sardines, mackerel, and sablefish, but many studies link diets high in leaner white fish with superior heart health.
 
 
Sources
  • El-Saed A, Curb JD, Kadowaki T, Okamura T, Sutton-Tyrrell K, Masaki K, Seto TB, Takamiya T, Choo J, Edmundowicz D, Evans RW, Fujiyoshi A, Nakamura Y, Miura K, Shin C, Kuller LH, Ueshima H, Sekikawa A. The prevalence of aortic calcification in Japanese compared to white and Japanese-American middle-aged men is confounded by the amount of cigarette smoking. Int J Cardiol. 2013 Jul 15;167(1):134-9. doi: 10.1016/j.ijcard.2011.12.060. Epub 2012 Jan 10.
  • El-Saed A, Sekikawa A, Zaky RW, Kadowaki T, Takamiya T, Okamura T, Edmundowicz D, Kita Y, Kuller LH, Ueshima H. Association of lipoprotein-associated phospholipase A2 with coronary calcification among American and Japanese men. J Epidemiol. 2007 Nov;17(6):179-85.
  • Kitamura A, Iso H, Naito Y, Iida M, Konishi M, Folsom AR, Sato S, Kiyama M, Nakamura M, Sankai T, et al. High-density lipoprotein cholesterol and premature coronary heart disease in urban Japanese men. Circulation. 1994 Jun;89(6):2533-9.
  • Sekikawa A, Curb JD, Ueshima H, El-Saed A, Kadowaki T, Abbott RD, Evans RW, Rodriguez BL, Okamura T, Sutton-Tyrrell K, Nakamura Y, Masaki K, Edmundowicz D, Kashiwagi A, Willcox BJ, Takamiya T, Mitsunami K, Seto TB, Murata K, White RL, Kuller LH; ERA JUMP (Electron-Beam Tomography, Risk Factor Assessment Among Japanese and U.S. Men in the Post-World War II Birth Cohort) Study Group. Marine-derived n-3 fatty acids and atherosclerosis in Japanese, Japanese-American, and white men: a cross-sectional study. J Am Coll Cardiol. 2008 Aug 5;52(6):417-24. doi: 10.1016/j.jacc.2008.03.047.
  • Sekikawa A, Miura K, Lee S, Fujiyoshi A, Edmundowicz D, Kadowaki T, Evans RW, Kadowaki S, Sutton-Tyrrell K, Okamura T, Bertolet M, Masaki KH, Nakamura Y, Barinas-Mitchell EJ, Willcox BJ, Kadota A, Seto TB, Maegawa H, Kuller LH, Ueshima H; for the ERA JUMP Study Group. Long chain n-3 polyunsaturated fatty acids and incidence rate of coronary artery calcification in Japanese men in Japan and white men in the USA: population based prospective cohort study. Heart. 2013 Dec 18. doi: 10.1136/heartjnl-2013-304421. [Epub ahead of print]
  • Sekikawa A, Ueshima H, Kadowaki T, El-Saed A, Okamura T, Takamiya T, Kashiwagi A, Edmundowicz D, Murata K, Sutton-Tyrrell K, Maegawa H, Evans RW, Kita Y, Kuller LH. Less subclinical atherosclerosis in Japanese men in Japan than in White men in the United States in the post-World War II birth cohort. Am J Epidemiol. 2007 Mar 15;165(6):617-24. Epub 2007 Jan 22.
  • University of Pittsburgh (UP). Eating Fish with High Levels of Omega-3 May Explain Very Low Levels of Heart Disease in Japan Compared to the U.S. Accessed at http://www.upmc.com/media/newsreleases/2008/pages/jacc-sekikawa.aspx
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