Findings of US-Swedish study affirm heart-failure benefits of omega-3s and non-fried fish
Health authorities worldwide agree that fatty fish and omega-3 fatty acids reduce key risk factors for a range of heart-related conditions.
These beneficial effects include lowering of elevated triglyceride (blood-borne fats), blood pressure, and heart rate levels, and reduced risk of arrhythmia (erratic heart beats).
They may explain a joint US-Swedish team's recent findings, which indicate that eating fatty fish in moderation may reduce the risk of heart failure.
Heart failure--known medically as congestive heart failure (CHF)--is a life-threatening condition that develops when the heart can no longer pump enough blood to meet the body's or its own needs.
Over time, the heart-muscle cells of people with CHF begin to weaken, work erratically, and eventually die.
CHF is the leading reason why people aged 65 and older become hospitalized. It's usually caused by high blood pressure and/or coronary artery disease. Heart failure is characterized by fatigue and weakness, difficulty walking, rapid or irregular heartbeat, and persistent cough or wheezing.
Prior research indicates that the omega-3s in fish reduce risk of CHF better than statin-type heart drugs can (See “Heart Failure Findings Favor Omega-3s over Statin Drug”).
And in recent years, Harvard researchers reported finding that people who eat fish enjoy a reduced risk of heart failure… as long as the fish is not fried in vegetable oil, which is typically high in pro-inflammatory omega-6 and trans fats:
“Among older adults, consumption of tuna or other broiled or baked fish, but not fried fish, is associated with lower incidence of CHF” (Mozaffarian D et al. 2003 and 2005).
US-Swedish study yields mysteriously mixed findings
For six years, from 1998 to 2004, researchers from Harvard Medical School and Sweden's Karolinska Institute followed 39,367 Swedish men aged 45 to 79.
They recorded details of the men's diets and tracked their health outcomes through Swedish inpatient and death registers.
All told, 597 men without a history of heart disease or diabetes developed CHF, and 34 of these died.
After comparing the participants' diets to their health outcomes, links were found between eating fatty fish or fish-borne omega-3s and a reduced risk of CHF.
However, CHF risk-reduction was only seen among men who averaged one serving of fatty fish a week, and who had a correspondingly moderate intake of marine omega-3s - about 300mg a day or 2,100mg per week.
A 3.5 oz serving of fatty fish like wild salmon, tuna, sardines, mackerel, or sablefish contains 1,000 to 2,000mg of omega-3s, so you'd get the weekly amount the study found beneficial (2,100mg) just by eating fatty fish once a week.
Eating more fatty fish than this did not give a greater benefit. In fact, to the researchers' surprise, eating more fish and omega-3s returned the chances of heart failure to the same level seen in men who never consumed any fatty fish or fish oil rich in marine omega-3s.
In a press release, Harvard cardiology fellow Dr. Emily Levitan speculated on the reasons why a moderate intake of fatty fish and omega-3s was associated with lower rates of heart failure in men, while men did not gain any benefit from eating more fish or omega-3 fish oil:
“The higher rate of heart failure in men who consumed the most fatty fish or marine omega-3 fatty acids… may be due to chance. Alternatively, these may be men in poor health who ate more fish to try to improve their ill-health, and therefore the fatty fish and fatty acids appear to be risk factors for heart failure. I suspect this is the most likely explanation...” (ESC 2009).
Dr. Levitan went on to make a key point: “Our study supports the idea that a healthy diet, including moderate consumption of fatty fish, can reduce the risk of cardiovascular diseases including heart failure” (ESC 2009).
Regular, moderate intake of omega-3s may help forestall heart failure
The men were divided into five groups depending on their intake of fatty fish… from very little or none, up to three or more servings a week.
The men in the middle group - who averaged one serving of fatty fish a week - had a 12 percent reduced risk compared to the men who never ate fatty fish: but this association that did not reach statistical significance.
But the men who ate more fish - either two servings a week or three or more servings a week - had nearly the same risk as the men who ate no fatty fish or fish oil.
The researchers also divided the men into five groups based on their intake of marine omega-3 fatty acids.
As seen with fish intake, the middle group--who consumed 360mg of omega-3s per day--were one-third less likely to have developed heart failure, compared with men who consumed fewer omega-3s (150mg to 220mg per day).
However, when it came to omega-3 intake, the association between moderate intake and reduced CHF risk did reach statistical significance
And again, as with higher fish intake, the men in the groups who consumed more omega-3s--about 460mg or 710mg per day--had a risk similar to men who consumed very few omega-3s.
The study could not provide evidence that taking fish oil supplements made any difference, mostly because the men in this study obtained most of their omega-3s from eating fish.
Odd outcomes attributed to confounding factors
The researchers cited two reasons why the results regarding consumption of fatty fish were not statistically significant, while the results on marine omega-3 fatty acids were significant, even though the omega-3s were mostly derived from eating fish, not fish oil supplements:
First, the men's omega-3 intake was adjusted for total energy (calorie) intake and age, while the frequency of fatty fish intake was not adjusted to account for these factors.
The adjustment for total energy intake was done because a given amount of marine omega-3s is not likely to have the same effect in a man who weighs 250 pounds as in a man who weighs 150 pounds. The adjustment for age was done because, in this population, the portion sizes varied quite a bit by age.
The second reason the results did not line up exactly is that the fish-intake and omega-3-intake categories were, of necessity, constructed differently. Fatty fish intake was divided up by frequency of consumption, and the very low- and very high-intake groups were small. In contrast, the men were divided into five equally sized groups according to marine omega-3 intake, which was adjusted for age and total energy intake.
All in all, these latest findings support the wisdom of taking fish oil and/or eating fatty fish to help ensure optimal heart health.
- European Society of Cardiology (ESC). Eating fatty fish and marine omega-3 fatty acids may reduce risk of heart failure. April 22, 2009. Accessed online at http://www.eurekalert.org/pub_releases/2009-04/esoc-eff042009.php
- Levitan EB, Wolk A, Mittleman MA. Fish consumption, marine omega-3 fatty acids, and incidence of heart failure: a population-based prospective study of middle-aged and elderly men. Eur Heart J. 2009 Apr 21. [Epub ahead of print]
- Mozaffarian D, Bryson CL, Lemaitre RN, Burke GL, Siscovick DS. Fish intake and risk of incident heart failure. J Am Coll Cardiol. 2005 Jun 21;45(12):2015-21.
- Mozaffarian D, Gottdiener JS, Siscovick DS. Intake of tuna or other broiled or baked fish versus fried fish and cardiac structure, function, and hemodynamics. Am J Cardiol. 2006 Jan 15;97(2):216-22. Epub 2005 Nov 21.
- Mozaffarian D, Lemaitre RN, Kuller LH, Burke GL, Tracy RP, Siscovick DS; Cardiovascular Health Study. Cardiac benefits of fish consumption may depend on the type of fish meal consumed: the Cardiovascular Health Study. Circulation. 2003 Mar 18;107(10):1372-7.