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LE Magazine February 2005
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Preventing Arrhythmia A Nutritional Guide to Keeping Your Heart in Rhythm

By William Davis, MD, FACC

Fish Oil: Powerful Heart Protection

Inexpensive, safe, and effective, fish oil is the closest thing we have to an ideal anti-arrhythmia agent. Fish oil is the most concentrated source of the omega-3 fatty acids eicosopentaenoic acid (EPA) and docosapentaenoic acid (DHA). Fish oil not only sharply reduces the frequency of irregular beats, but also diminishes the likelihood of death from dangerous arrhythmias. It also increases desirable heart-rate variability, probably by favorably influencing parasympathetic nervous system tone.1 Fish oil achieves all this without significant side effects, an advantage lacking in every prescription anti-arrhythmia medication.

The Diet and Reinfarction Trial, or DART, was the first randomized clinical trial demonstrating the benefits of fish oil versus placebo. Conducted by Dr. Michael Burr at the University of Wales in 1989, the trial enrolled 2,033 men who had had a previous heart attack. Those who ate fish twice a week saw a 29% drop in all-cause death. Curiously, there was no decrease in the number of heart attacks, only in deaths from heart attack. Dr. Burr and his colleagues reasoned that fish oil likely suppresses abnormal rhythms generated by damaged heart muscle.2

The GISSI-Prevenzione trial, an Italian study reported in 1999, persuasively confirmed fish oil’s anti-arrhythmic benefits.3 In this large trial, more than 11,000 subjects who had recently survived a heart attack took either a combined 1000 mg daily of EPA and DHA, or placebo. Those receiving fish oil experienced a 20% reduction in total mortality,3 with much of the benefit attributable to a 53% reduction in sudden cardiac death that emerged during follow-up at four months.4

Fish oil’s rhythm-suppressing properties are so effective that some cardiologists are now recommending that patients with implanted defibrillators, which are used only for life-threatening heart rhythms, take fish oil to reduce their hearts’ rhythm instability and to cut down on defibrillator firings, which are both painful and frightening.

What about taking fish oil to prevent dangerous rhythms in people without known heart disease? The Physicians’ Health Study provides some perspective. During 11 years of observation, participants who died from sudden death had much lower blood levels of omega-3 fatty acids than those who did not. Eating just one or more servings of fish weekly yielded a 52% reduction in the risk of sudden death.5

Numerous experimental preparations have demonstrated that fish oil powerfully inhibits the cellular phenomena that drive arrhythmias. By contrast, arachidonic acid, which results from intake of omega-6 fatty acids, increases the potential for arrhythmias. Fish oil also reduces the blood-clotting protein fibrinogen and inhibits platelet aggregation, which prevents blood-clot formation on active, ruptured coronary plaque that would otherwise result in heart attack.6

An intriguing but unanswered question is whether fish oil suppresses the common rhythm called atrial fibrillation, which occurs when the heart’s two small upper chambers quiver instead of beating effectively. Because blood is not pumped out of the atria effectively, it can pool and clot, increasing the risk for stroke. Atrial fibrillation plagues around 10% of people aged 80 and over, and is a frequent cause of hospitalization. Conven-tional medical treatment for atrial fibrillation is fraught with side effects and is of limited effectiveness, and better therapies are sorely needed.7 Fish oil has impressively suppressed atrial fibrillation in experimental non-human preparations.8 People who suffer from this rhythm also have significantly lower levels of omega-3 intake.9 Does taking fish oil prevent this terribly common rhythm? That question remains unanswered, yet the evidence supporting fish oil supplementation is so compelling for other reasons that it is difficult to argue against a preventive use of fish oil for this purpose.

A secondary source of omega-3 fatty acids is alpha-linolenic acid (ALA), found in flaxseed, walnuts, and canola oil. When humans ingest ALA, however, only 10% of it is converted into active EPA or DHA, while most of the rest is simply burned for calories. The preponderance of existing data suggests that fish oil capsules delivering a daily dose of approximately 1000-2000 mg of EPA and DHA are likely to yield substantial heart-rhythm benefits. Conventional fish oil preparations contain 30% EPA and DHA, or 300 mg of EPA/ DHA per 1000-mg capsule.

Heart Benefits of Magnesium

Magnesium is a crucial nutrient that helps ensure the proper functioning of approximately 300 enzymes in the human body. Unfortunately, the average Amer-ican ingests substantially less than the daily recommended dietary allowance (RDA) of 420 mg of magnesium for men and 320 mg for women. Daily deficiencies of 10% or more are common.10

Moreover, several epidemiological studies have demonstrated that magnesium intake is dropping precipitously as Americans consume ever greater amounts of magnesium-depleted processed foods. Soft drinks are manufactured using de-ionized water and are essentially devoid of magnesium. Carbon-ated beverages like soda contain phosphates that bind magnesium in the intestinal tract, making it unavailable for absorption. To make matters worse, more of us are drinking bottled water, and most retail brands contain little or no magnesium.

Even tap water is adding to the problem. As municipal and home water-treatment systems convert “hard” water into “soft” water, magnesium is removed. Meas-urable increases in the risk of sudden death have been reported in municipalities with the lowest levels of magnesium in their drinking water.11 A recent World Health Organization report on the quality of drinking water cited 80 studies that have examined the relationship between cardiovascular death and water “hardness” (measured principally by magnesium and calcium content). The report concluded that the magnesium content of water is indeed a cardiovascular risk and should become a priority for water supplementation.12

Magnesium blood levels are routinely monitored in hospitalized patients, particularly if diuretics are administered. It is a fact that when magnesium blood levels are low, arrhythmia tends to occur. Premature or irregular heartbeats are common, as are nuisance rhythms like supraventricular tachycardia. Dangerous ventricular rhythms such as ventricular tachycardia and Torsade de Pointes can also result. People suffering from congestive heart failure are especially susceptible to these rhythms when magnesium levels are low. People prone to atrial fibrillation can suffer recurrences due to low magnesium levels. Though not as immediately life threatening as ventricular rhythms, atrial fibrillation can still necessitate complicated treatments and increase the risk of stroke.13

The problem with measuring blood levels of magnesium is that they are poor indicators of the body’s true (intracellular) magnesium levels. If blood magnesium levels are low, then cellular magnesium levels are undoubtedly low as well. If blood magnesium levels are normal, however, one may still have low tissue levels of magnesium. The most striking reduction in tissue magnesium is found in the heart muscle, or myocardium. Unfortunately, determining tissue magnesium levels is not easy in living, breathing humans. In one study, only 8% of coronary patients were found to be low in blood measures of magnesium, but tissue levels of magnesium were found to be depleted in 53% of the subjects.14 Some cardiologists will therefore administer intravenous magnesium to patients with rhythm disorders, even when blood magnesium is in the normal range.

How do you know whether your magnesium level is low? Several signs can tip you off:

  • Cardiac arrhythmias. Having any sort of arrhythmia should compel your physician to question whether you have adequate magnesium levels, as low magnesium levels potentiate (that is, render active or potent) abnormal heart rhythms. With rare exceptions, you cannot rely on magnesium alone to treat abnormal rhythms; however, magnesium can be a useful preventive strategy to help avoid developing such rhythms in the first place. Magnesium can also serve as an adjunctive therapy to prescribed anti-arrhythmia treatments.
  • Low potassium. Potassium is another electrolyte that is commonly depleted by diuretics and may be deficient in certain disease states. Like magnesium, potassium may not be fully replenished by diet. Low magnesium commonly accompanies low potassium.
  • Muscle cramps. Leg cramps, especially those that occur at night, can signal a magnesium deficiency. Leg cramps that occur with physical activity such as walking, however, are usually due to atherosclerotic blockages in the leg or abdominal arteries, not to low magnesium.
  • Tremors. The presence of tremors is a complex symptom to diagnose, but some people with tremors will respond to magnesium.
  • Anxiety, weakness. Non-specific symptoms such as anxiety and weakness occasionally respond to magnesium supplementation.

While the treatment of specific abnormal heart rhythms should be left to your physician or cardiologist, ensuring sufficient magnesium intake is an excellent preventive strategy that is strongly supported by the scientific literature. This is especially true if you have been prescribed a diuretic for treatment of hypertension, congestive heart failure, or edema, or for other reasons. Favorable magnesium levels in the body tend to make rhythms like atrial fibrillation and supraventricular tachycardias—as well as dangerous ventricular rhythms such as ventricular tachycardia and Torsade de Pointes—less likely to occur.15 Although some investigators have argued that magnesium administered during acute heart attack does not reduce the risk of dying from fatal heart rhythms,16 magnesium can be very effective in less dire situations.

Because low magnesium tissue levels are virtually endemic in the US, magnesium supplementation should be practiced by nearly everyone. Many epidemiologists have proposed supplementing tap water with magnesium, just as fluoride is added to prevent tooth decay. Magnesium supplements are safe and inexpensive, and the only side effect is diarrhea, which generally occurs with daily doses in excess of 250 mg. For this reason, many over-the-counter laxatives contain magnesium; however, long-term use of laxatives is not advised without medical supervision. For magnesium supplementation, a recommended dose is 300-500 mg daily. Magnesium citrate is a convenient, highly absorbable form that provides elemental magnesium in a capsule form. Magnesium is best taken in distributed doses throughout the day in order to avoid diarrhea. Good dietary sources of magnesium are shown in the accompanying sidebar, “Foods Rich in Magnesium.”

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