Nutrition Research

Summary

Cardiac arrhythmia, or abnormal heart rhythm, can lead to ineffective pumping by the heart and, if prolonged and severe, sudden cardiac death (SCD). Although randomized controlled trials have not demonstrated a clear clinical benefit for omega-3 fatty acid supplements, a large body of evidence indicates that regular consumption of fish significantly reduces the risk of SCD. Regular consumption of nuts, and light-to-moderate consumption of alcoholic beverages are also associated with a significantly reduced risk of SCD. Moderate coffee consumption (three to four cups per day) is not associated with cardiac arrhythmia in healthy individuals. Some medications can lead to abnormally high or low blood potassium concentration, which increases the risk of cardiac arrhythmia.

Condition Overview

Cardiac arrhythmia, or abnormal heart rhythm, refers to any change from the normal sequence of electrical impulses in the heart. The electrical impulses that initiate a heartbeat may be too fast, too slow, or inconsistent. When the heart does not beat properly, it cannot pump blood effectively, potentially causing problems for the heart itself or for the rest of the body.

For example, blood may pool inside the chambers of the heart during arrhythmia. Pooled blood may form clots, which can break free and block an artery, leading to heart attack or stroke. If arrhythmia is prolonged and severe, the heart may be unable to pump any blood at all. The abrupt loss of heart function when the electrical system malfunctions is called sudden cardiac arrest. Sudden cardiac arrest can lead to sudden cardiac death if the normal rhythm of the heart is not reestablished.

Arrhythmia may result from a heart defect present since birth, the use of certain drugs and medications, or as a consequence of damage to the heart’s muscular or electrical system due to heart failure, heart attack, high blood pressure, coronary heart disease, thyroid abnormalities, or rheumatic heart disease.

See below for specific information about nutrients and dietary factors relevant to arrhythmia.

Types of Arrhythmia

Tachycardia - too rapid heart rate
Bradycardia - too slow heart rate
Atrial Fibrillation - rapid, uncoordinated beating of the atria that results in ineffective atrial contractions; atrial fibrillation is a major cause of stroke
Ventricular Fibrillation - rapid, uncoordinated beating of the ventricles that results in ineffective pumping of the heart; ventricular fibrillation can cause cardiac arrest

DEFINITIONS
Arrhythmia - abnormal heart rhythm
Atria (singular: atrium) - the two upper chambers of the heart that receive blood from the veins and contract to force blood into the ventricles
Ventricles - the two lower chambers of the heart that contract to force blood to the lungs (right ventricle) and to the rest of the body (left ventricle)

Nutrition Research

DEFINITIONS
Test tube (in vitro) experiment - a research experiment performed in a test tube, culture dish, or other artificial environment outside of a living organism; in vitro is a Latin phrase meaning in glass
Animal experiment - a research experiment performed in a laboratory animal; many different animal species are studied in the laboratory, including terrestrial (land), aquatic (water), and microscopic animals
Observational study - a human research study in which no experimental intervention or treatment is applied, and participants are simply observed over time
Randomized controlled trial - a human research study in which participants are assigned by chance alone to receive either an experimental agent (the treatment group) or a placebo (the control group)
Placebo - a chemically inactive substance


Omega-3 Fatty Acids

What they do

General

  • Essential fatty acids are a type of polyunsaturated fatty acid (PUFA). PUFAs have several double bonds in their structure that give them complex shapes and influence their function.
  • Essential fatty acids are structural components of every cell in the body, are converted to compounds that influence inflammation and immunity, and serve as an important source of energy.
  • There are two classes of essential fatty acids: omega-6 PUFA and omega-3 PUFA.

Arrhythmia-specific

  • Test tube and animal experiments indicate that the long-chain omega-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), help stabilize ischemic heart muscle cells and reduce susceptibility to arrhythmias.
What we know
  • Regular fish consumption is inversely associated with the risk of sudden cardiac death (SCD). In other words, the more fish consumed, the lower the risk of SCD. 
  • A pooled analysis of nine randomized controlled trials found no significant effect of omega-3 fatty acid supplements on SCD or ventricular arrhythmias in patients with previous heart attack. Notably, although the pooled analysis reported no significant effect, the included trials reported either a protective effect or no effect, with no harmful outcomes reported.
  • Although supplementation trials have not demonstrated a clear clinical benefit of omega-3 fatty acid supplements, a large body of evidence indicates that consumption of at least 250 milligrams/day of long-chain omega-3 fatty acids, especially by eating fatty fish, helps reduce the risk of cardiovascular-related death, including fatal myocardial infarction (heart attack) and SCD.
DEFINITIONS
Ischemia (adjective: ischemic) - inadequate blood supply to an organ or tissue
Inverse association - a relationship between two variables in which they move in opposite directions

For references and more information, see the section on long-chain omega-3 fatty acids and sudden cardiac death in the Essential Fatty Acids article.

There are two essential fatty acids: linoleic acid (an omega-6 polyunsaturated fatty acid) and alpha-linolenic acid (an omega-3 polyunsaturated fatty acid). These fatty acids are considered essential nutrients because they cannot be made in the body and must be consumed in the diet. Vegetable oils, especially safflower oil, sunflower oil, and corn oil, are a good source of linoleic acid.Flax and chia sees, walnuts, canola oil, and soybean oil are good sources of alpha-linoleic acid. Inside body tissues, the essential fatty acids are converted to long-chain fatty acids. Due to low efficiency of conversion, it is recommended to obtain eicosapentaenoic acid (EPA) and docosapentaenoic acid (DHA) from additional sources. Oily fish, fish oil supplements, krill oil supplements, and algae oil supplements are good sources of EPA and DHA.

[Click to Enlarge]

 

back to top of page

 

Potassium

What it does

General

  • Potassium is an essential mineral that helps maintain fluid and electrolyte balance, influences blood pressure, and is required for proper nerve conduction and muscle contraction.

Arrhythmia-specific

  • Severe hyperkalemia (abnormally high blood potassium) and hypokalemia (abnormally low blood potassium) may result in cardiac arrhythmias that can be fatal.

For a table of medications associated with hyperkalemia and hypokalemia, see the safety section in the Potassium article.

Potassium Flashcard. Main Functions: (1) maintains fluid and electrolyte balance, (2) Required for proper nerve conduction and muscle contraction, and (3) Influences blood volumen and blood pressure. Good Sources: Fruit (prunes, banana, orange juice); prunes (dried plums), one-half cup, 637 mg; banana, 1 medium, 422 mg; Vegetables (potato, tomato, artichoke), potato with skin, 1 medium, 926 mg. Daily Recommendation. 4,700 mg for adults. Special Notes: (1) Potassium and sodium work together. A diet high in potassium and low in sodium helps maintain a lower blood pressure. (2) Fruit, vegetables, and legumes are naturally high in potassium and low in sodium. (3) Most people consume too little potassium. In addition to fruit and vegetables, nuts and beans also provide potassium.

[Download PDF]

back to top of page

 

Alcoholic Beverages

What they do

General

  • Alcoholic beverages contain ethanol and other ingredients with bioactive properties that may affect health.
  • When consumed in moderation (no more than two drinks/day for men and one drink/day for women), alcoholic beverages have been associated with beneficial effects in the cardiovascular system.
  • On the other hand, heavy alcohol consumption (more than five drinks/day) has been consistently associated with negative effects in many organ systems.

Arrhythmia-specific

  • The ways by which alcohol may trigger arrhythmias are not fully known. Alcohol may interfere with the contractility of heart muscle cells, change the shape and structure of heart muscle cells, contribute to electrolyte imbalance, or induce oxidative stress. 
What we know
  • Binge drinking (more than five drinks on a single occasion) and chronic, high alcohol consumption (more than two drinks/day) are associated with an increased risk of atrial fibrillation.
  • For sudden cardiac death (SCD), the relationship with alcohol consumption appears to be “J shaped,” meaning that light-to-moderate alcohol consumption is associated with a reduced risk while no alcohol or high alcohol consumption are associated with an increased risk of SCD. 

For references and more information, see the section on Health Risks Associated with Alcohol Consumption in the Alcoholic Beverages article.

back to top of page

 

Coffee

What it does

General

  • Coffee is a complex mixture of chemicals. In addition to caffeine, coffee contains several phytochemicals that can influence human health.

Arrhythmia-specific

  • Caffeine binds to certain nerve cell receptors, leading to stimulatory effects in the nervous system.  
What we know
  • Observational studies have found no association between moderate coffee consumption (three to four cups/day) and atrial fibrillation or sudden cardiac death.
  • Likewise, electrophysiology studies have found that caffeine ingestion up to 500 milligrams (mg)/day (equivalent to five to six cups of coffee per day) does not increase the frequency or severity of cardiac arrhythmia in healthy individuals or in those with coronary heart disease.

For references and more information, see the section on cardiac arrhythmias in the Coffee article.

Additional references

  • Katan JB and Schouten E. Caffeine and Arrhythmia. American Journal of Clinical Nutrition. 2005;81:539-40
  • Pelchovitz DJ & Goldberger JJ. Caffeine and Cardiac Arrhythmias: A Review of the Evidence. American Journal of Medicine. 2011;124:284-9

back to top of page

 

Nuts

What they do

General

  • Nuts are a good source of soluble fiber, phytosterols, mono- and polyunsaturated fatty acids, protein, certain vitamins (folate, vitamin E), and minerals (calcium, magnesium, potassium).
  • Examples of tree nuts include: almonds, Brazil nuts, cashews, hazelnuts, macadamia nuts, pecans, pistachios, and walnuts.
  • Peanuts are not nuts; they are legumes. However, peanuts are nutritionally similar to tree nuts and have some of the same beneficial health effects.

Arrhythmia-specific

  • There are several ways by which nut consumption could affect arrhythmia and the risk of sudden cardiac death (SCD):
    • Nuts provide small amounts of omega-3 fatty acids, which have been shown to exert anti-arrhythmic effects.
    • Regular nut consumption is associated with an improved blood cholesterol profile, which is thought to reduce the risk of SCD.
    • Replacing saturated fat with omega-6 and omega-3 PUFA, which are abundant in nuts, reduces the risk of SCD. 
What we know
  • Regular nut consumption (one ounce at least five times per week) is associated with a significantly lower risk of cardiovascular disease.
  • When looking at SCD specifically, higher dietary intake of nuts has been associated with a significantly reduced risk of SCD in healthy, middle-aged men. No association between nut consumption and atrial fibrillation was observed in this same study population.

For references and more information, see the section on cardiovascular disease in the Nuts article.

HIGHLIGHT
  • Nuts are packed with healthy fats, and therefore, calories.
  • One ounce (28 grams) of nuts contains approximately 160 calories and 14 to 19 grams of fat (mainly mono- and polyunsaturated fatty acids).
  • One ounce of nuts equals approximately: 24 almonds, 8 medium Brazil nuts*, 18 medium cashews, 12 hazelnuts, 12 macadamia nuts, 15 pecan halves, 47 pistachios, 14 walnut halves, and 35 peanuts.
  • It is recommended to substitute nuts for sources of saturated fat.

*Depending on growth conditions, a single Brazil nut could contain exceedingly high levels of selenium.  

Additional references

  • Burke AP, et al. Coronary Risk Factors and Plaque Morphology in Men with Coronary Disease Who Died Suddenly. New England Journal of Medicine. 1997;336:1276-82
  • Khawaja O, et al. Nut Consumption and Risk of Atrial Fibrillation in the Physicians’ Health Study. Nutrition Journal. 2012;11:17
  • Dreher ML & Maher CV. The Traditional and Emerging Role of Nuts in Healthful Diets. Nutrition Reviews. 1996;54(8):241-5