As people age, their heart valves and chambers can gradually thicken and stiffen, making it harder to pump blood efficiently.
This stiffening process – known as cardiac fibrosis – is exacerbated by chronic cardiac inflammation, heart attacks, heart infections, heart failure, and high blood pressure (Zhang R et al. 2010; Nagai T et al. 2011).
When heart muscles are injured, special cells called fibroblasts respond by covering the wounded area with layers of “matrix” proteins … primarily collagen.
Chronic inflammation can worsen or accelerate fibrosis by promoting collagen “cross-linking” – a pathological process that produces stiff, inflexible connective tissue.
The most common cause of cardiac fibrosis is chronic hypertension … and the most common outcomes are heart valve dysfunctions that in turn lead to congestive heart failure (Cocker MS et al. 2009).
And chronic over-exertion may be another culprit. A clinical study in elite male and female endurance athletes aged 19 to 45 found cardiac fibrosis in three out of four … probably due to the extreme heart stress produced by intense, prolonged exercise (Cocker MS et al. 2008).
Let’s take a look at two related studies in rats, which reveal a whole new way in which omega-3s from fish oil – but not omega-3s from plant foods – can be very heart healthy.
First, we’ll summarize a University of Maryland rat study from 2009, and then describe newly published findings from a similar experiment in mice.
Omega-3s prevented hypertension-related fibrosis in rats
Two years ago, researchers from the University of Maryland-Baltimore published the intriguing results of a study focused on “left ventricular hypertrophy”.
Called LVH for short, this condition is an enlargement (hypertrophy) of the muscle tissue that forms the wall of the heart’s main pumping chamber (Duda MK et al. 2009).
And like cardiac fibrosis in heart valves, LVH is most commonly and likely caused by buildup of excess collagen in response to chronic hypertension, exacerbated by low-grade inflammation.
Having LVH forces the heart to work harder, which eventually causes the walls of the left ventricle chamber to thicken, lose elasticity and blood-pumping power.
The Maryland team divided rats into three groups, fed either fish oil omega-3s, plant-derived omega-3s, or no omega-3s.
The group that got omega-3 fish oil received doses corresponding to the ones typically taken by people.
In other words, the omega-3s in the rats’ diets constituted percentages of total daily calories similar to the percentages provided by standard human doses of fish oil (250-500mg of omega-3s daily).
After artificially inducing high blood pressure in all of the rats, the Baltimore-based scientists watched what happened to the animals’ hearts.
The rats that got omega-3 EPA and DHA from fish oil showed no thickening of their heart-chamber walls, or any loss of pumping power.
In contrast, the rats that got either no omega-3s at all, or only plant-derived omega-3s, developed fibrosis in their left ventricle and impaired blood pumping performance from that chamber.
The fish oil group also showed a dose-dependent increase in levels of the hormone-like anti-inflammatory chemical adiponectin … and the animals showing the biggest boost in adiponectin also had the least LV chamber enlargement.
As would be expected based on the results of many prior studies in animals and humans, the blood of the rats receiving fish oil was also less “sticky”, with lower levels of inflammation markers.
As the authors put it, “Dietary supplementation with omega-3 PUFA derived from fish, but not from vegetable sources, increased plasma adiponectin, suppressed inflammation, and prevented cardiac remodeling and dysfunction under pressure overload conditions.” (Duda MK et al. 2009)
Now, a similar study in mice supports the hope that fish-derived omega-3s may help prevent cardiac fibrosis.
Fish-derived omega-3s deterred fibrosis in mice
In the study making headlines this week, Dr. Martin Gerdes of New York College of Osteopathic Medicine and colleagues in South Dakota report that omega-3s from fish protected mouse hearts from cardiac fibrosis.
“We have observed something very exciting,” said Gerdes. Although his research involved mice, not men, he expressed a belief that the findings are pretty likely to apply to people as well.
Dr. Gerdes’ team divided mice into two groups, with one receiving fish oil as part of their diet, while the control group got the same diet minus fish oil.
All of the mice were then subjected to a procedure that artificially induces high blood pressure, to see what effect fish oil might have on development of fibrosis and reduced pumping power in the animals’ left ventricle heart chambers.
As hoped, the fish oil group showed no activation of cardiac fibroblasts, no excess collagen, no cardiac dysfunction, and no signs of cardiac fibrosis.
In addition, the artery linings of the fish oil group also showed increased production of nitric oxide, which helps keep blood vessels open.
In contrast, the cardiac fibroblasts in the control group produced excess collagen and the animals developed significant cardiac dysfunction and cardiac fibrosis.
We cannot be certain that these results translate to humans, and there is no ethical way to conduct a clinical trial to test that prospect.
But given the great similarities among rats, mice, and men when it comes to cardiac fibrosis and metabolism of omega-3s, these similar findings from two studies provide another reason to consider fish and fish oil heart healthy.
Chen J, Shearer GC, Chen Q, Healy CL, Beyer AJ, Nareddy VB, Gerdes AM, Harris WS, O'Connell TD, Wang D. Omega-3 Fatty Acids Prevent Pressure Overload-Induced Cardiac Fibrosis Through Activation of Cyclic GMP/Protein Kinase G Signaling in Cardiac Fibroblasts. Circulation. 2011 Feb 15;123(6):584-93. Epub 2011 Jan 31.
Cocker MS et al. Abstract 4194: Increased Incidence of Myocardial Fibrosis with Reduced Cardiac Function in Elite High-Endurance Athletes: A Cardiovascular Magnetic Resonance (CMR) Study. Circulation. 2008;118:S_840.
Cocker MS, Abdel-Aty H, Strohm O, Friedrich MG. Age and gender effects on the extent of myocardial involvement in acute myocarditis: a cardiovascular magnetic resonance study. Heart. 2009 Dec;95(23):1925-30. Epub 2009 Aug 25.
Duda MK, O'Shea KM, Tintinu A, Xu W, Khairallah RJ, Barrows BR, Chess DJ, Azimzadeh AM, Harris WS, Sharov VG, Sabbah HN, Stanley WC. Fish oil, but not flaxseed oil, decreases inflammation and prevents pressure overload-induced cardiac dysfunction. Cardiovasc Res. 2009 Feb 1;81(2):319-27. Epub 2008 Nov 17.
Nagai T, Anzai T, Kaneko H, Mano Y, Anzai A, Maekawa Y, Takahashi T, Meguro T, Yoshikawa T, Fukuda K. C-reactive protein overexpression exacerbates pressure overload-induced cardiac remodeling through enhanced inflammatory response. Hypertension. 2011 Feb;57(2):208-15. Epub 2011 Jan 10.
Zhang R, Zhang YY, Huang XR, Wu Y, Chung AC, Wu EX, Szalai AJ, Wong BC, Lau CP, Lan HY. C-reactive protein promotes cardiac fibrosis and inflammation in angiotensin II-induced hypertensive cardiac disease. Hypertension. 2010 Apr;55(4):953-60. Epub 2010 Feb 15.