One in every four American adults has high blood pressure – also known as hypertension.
Yet, nearly one in three don't know it … and the only way to find out is through regular checkups.
 Surprisingly, most cases of high blood pressure have no obvious cause (see our sidebar, “About high blood pressure”).
So it makes sense to adopt lifestyle habits that can help prevent or reduce hypertension.
Omega-3s and blood pressure
For decades, it's been clear that the long-chain omega-3 fatty acids in seafood (DHA and EPA) can produce a relatively small but significant drop in blood pressure.
About high blood pressure
When your heart pumps blood, this exerts force against the walls of your arteries.
When that force becomes too great, it's called high blood pressure or hypertension.
Blood pressure is affected by the amounts of water and salt in your body, the condition of your kidneys, nervous system, or blood vessels, and the levels of certain hormones
It typically rises in middle age and beyond as your blood vessels become stiffer … and high blood pressure raises the risk of stroke, heart attack, heart failure, kidney disease, and early death.
The risk of hypertension is greater if you are diabetic, African-American, obese, stressed, anxious, drink too much alcohol, eat too much salt, smoke, or have a family history of high blood pressure
High blood pressure that's been caused by a medical condition or drug is called “secondary” hypertension.
However, in most cases, high blood pressure has no certain cause … in which case, doctors call it “essential” hypertension.
Untreated hypertension can lead to stroke, heart disease, kidney failure, and eye problems.
Certain symptoms can signal hypertension:
  • Chest pain
  • Vision problems
  • Severe headache
  • Difficulty breathing
  • Irregular heartbeat
  • Blood in the urine
  • Fatigue or confusion
  • Pounding in your chest, neck, or ears
If you have any of these symptoms, see a doctor immediately. You could be having a hypertensive crisis that could lead to a heart attack or stroke.
These so-called “marine” omega-3s produce several effects that combine to discourage hypertension:
  • Moderate inflammation and relax/widen arteries.
  • Enhance generation of endothelial nitric oxide (NO).
  • Beneficially activate the parasympathetic nervous system.
  • Reduce expression of tumor growth factor-beta (TGF-beta).
  • Regulate vasomotor tone and sodium excretion from kidneys.
  • Reduce angiotensin-I-converting enzyme (ACE) activity and angiotensin-II formation.
  • Compete with omega-6 fatty acids for incorporation into cell membranes, thereby reducing the body's production of pro-inflammatory, artery-stiffening/narrowing agents (eicosanoids).
Explanations of some of these beneficial effects are in order.
Vasomotor tone is the level of nervous stimulation of the muscles in your blood vessel walls when you are not exercising. If it is too high, hypertension can result.
Likewise, excessive expression of the genes that produce TGF-beta is now implicated in hypertension.
And as its name implies, the body's angiotensin-I-converting enzyme (ACE) converts angiotensin I to angiotensin-II, which is a potent vasoconstrictor (artery-narrowing agent).
Accordingly, greater production of ACE tends to narrow arteries and thereby raise blood pressure … and anything that inhibits ACE production in the body helps control blood pressure.
That negative effect of ACE brings us to today's story … which underscores the benefits of whole foods, as more than delivery vehicles for single nutrients.
We should stress that the new findings do not imply that seafood is a substitute for blood pressure drugs.
Nor is it likely that a serving of fish or shellfish will have the same artery-relaxing effect as a supplement that delivers a large amount of their hypertension-curbing peptides.
Instead, research on seafood peptides bolsters the idea that the myriad components of whole foods produce synergistic benefits beyond any one of them alone.
Seafood and hypertension: the ACE link
Peptides consist of two or more amino acids bonded in a chain and enclosed within a protein molecule.
Most peptides in foods only become “bioactive” when digested by enzymes in the gastrointestinal tract, or via food processing or fermentation (e.g., yogurt and fermented beans or vegetables).
A growing body of evidence suggests that peptides (protein fragments) found in dairy foods and legumes (beans) offer ACE-related blood pressure benefits.
However, peptides unique to some fish and shellfish appear to exert much greater ACE-inhibiting effects than those found in other foods.
And the effects of these seafood peptides may be substantially stronger than the ACE-inhibiting impacts associated with their omega-3s.
Various seafood species contain ACE-inhibiting peptides that have reduced blood pressure in rodents as or more effectively than standard medications can … without those drugs' side effects.
Researchers have found potent ACE-inhibiting peptides in sardines, anchovies, oysters, mussels, big eye and yellowfin tuna, clams, Asian shrimp, Alaskan pollock, Pacific hake, cuttlefish (squid), bonito, shark, others ... with many more species left to be tested.
Now, Norwegian scientists report the strongest ACE-inhibiting peptide ever tested, which occurs naturally in tasty Arctic prawns (Pandalus borealis) … a type of shrimp.
The unprecedented outcome of this combined rat and test tube study have prompted the Norwegian agency to commission a clinical trial, to see if the findings apply to people.
Rat study finds potent anti-hypertension proteins in prawns
The prawn-peptides study comes from NOFIMA … a scientific consortium of Norwegian food and health ministries, and Europe's largest institute for applied fisheries and food research.
Lead author Asbjørn Gildberg said the results were not necessarily limited to this particular type of shrimp.
“These are the highest [ACE-inhibiting effects] seen but [peptide] hydrolysates from Chinese shrimps have indicated levels almost as good,” he said. “The human trial data will be very interesting.”
(Peptide hydrolysates are simply isolated peptides produced by the process of hydrolysis, which involves breaking down the molecular bonds in proteins using heat and either acid or alkali solutions. Hydrolysis of proteins into peptides also happens in your digestive tract.)
As the researchers wrote: “The measurements by two independent methods both revealed higher in vitro [test tube] ACE-inhibitory activity … than earlier reported in comparable [peptide] hydrolysates.”
“An introductory feeding trial with spontaneously hypertensive rats indicated positive in vivo results ...”. (The term in vivo means experiments in animals (or people), as opposed to tests performed on isolated tissues or cells, which are called in vitro.)
“Although further in vivo studies are necessary to verify the antihypertensive potential, the very high in vitro ACE-inhibitory activity reveals that the shrimp protein hydrolysate is a promising candidate for nutraceutical application.”
NOFIMA worked with Norwegian biotech firm Marealis, which develops bioactive peptides from sustainable Arctic Ocean sources, and partly funded the studies.
Are seafood peptides superior?
While milk, soy, and other food sources of anti-hypertensive peptides work well in test tube studies, they are not always active in animals or humans.
Certain seafood peptides seem to be more effective because they are absorbed intact while peptides other foods are broken down by digestive enzymes.
Three clinical studies have shown that fish peptide supplements can exert significant blood pressure-lowering effects in people with high blood pressure.
And supplements containing isolated fish peptides appear to be effective in two-thirds of people with high blood pressure … about the same percentage as common ACE-inhibiting drugs.
That said, we need more research to determine whether eating seafood species known to contain potently anti-hypertensive peptides produces a measurable effect, and over what time period.
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