Salt, the main source of dietary sodium, is consumed both as seasoning and in processed foods. High intake of salt contributes to hypertension, a risk factor for coronary heart disease which, in turn, is related to sudden cardiac death. Similarly, atrial fibrillation indicates cardiovascular disease and is known to cause strokes.

Summary: Researchers from Oulu University Hospital in Oulu, Finland, looked at the relationship between dietary salt consumption and the onset of atrial fibrillation, the most common arrhythmia. Their findings—the first of their kind, according to the study’s authors—suggest high sodium consumption may increase the risk of atrial fibrillation, even when the patient does not have high blood pressure.  

The study: For 19 years, researchers followed the diets and heart health of 1,200 people with a mean age of 51.5 years at recruitment. For each person with hypertension, researchers matched a person of the same age and gender who did not have hypertension. If a subject experienced atrial fibrillation and visited a hospital for it, the patient’s data was included in the study, but the patient no longer participated.

The findings: The 25 percent of subjects with the highest dietary sodium consumption had the highest chance of experiencing atrial fibrillation, 16.8 percent, compared with the 25 percent of subjects who had the lowest dietary consumption, 6.7 percent.

The subjects who experienced atrial fibrillation were older; had higher body mass index (BMI) and waist circumference; longer experience smoking; and consumed more sodium than subjects who were not diagnosed with atrial fibrillation.

Study conclusions: Sodium consumption and atrial fibrillation were related even after other risk factors such as age, gender and smoking were accounted for. More studies are needed.

It’s possible that sodium increases the risk of atrial fibrillation because it enhances inflammation and fibrosis in the atrium. Until more research is completed, it’s not known how sodium intake causes risk of atrial fibrillation, however.

Because of the size of the study, the low number of atrial fibrillation incidents and the subjects’ self-reporting their diets, the authors cautioned that they can only suggest a relationship between dietary sodium intake and atrial fibrillation events.

Why the research is interesting: The study provides more evidence that even if a subject does not have high blood pressure, consuming high amounts of salt can increase the person’s chance of suffering a stroke, atrial fibrillation and other cardiac problems.

Current RDAs: The U.S. Centers for Disease Control and Prevention recommend that everyone age 14 or older should consume less than 2,300 mg of dietary sodium per day. Data from the 2009-2012 National Health and Nutrition Examination Survey showed that 89 percent of adults and more than 90 percent of children exceeded this recommendation. Among adults with hypertension, 86 percent ate more than 2,300 mg per day. Of adults 19 or older, 98 percent of men and 80 percent of women consumed more than the recommended amount of sodium; and 90 percent of adult whites, compared with 85 percent of adult blacks, exceeded the recommended limit.

Who and when: Of the 716 subjects whose data were reviewed for the study, 165 men and 177 women were hypertensive; 180 men and 194 women were not. Men were recruited from December 1990 to May 1992, and the women were recruited one year later. Subjects were followed until they were diagnosed with atrial fibrillation or until December 2009, whichever came first.

Men in the study consumed more sodium than women did: a mean of  4,174 mg per day compared with a mean of 2,883 mg per day. The 25 percent of subjects with the highest levels of sodium consumption included 109 men (60.9 percent) and 70 women (39 percent). Only three subjects (0.4 percent) consumed the recommended 2,300 mg or less per day.

What was measured: Sodium consumption (based on food records), level of smoking; alcohol consumption and medications were self-reported. Weight, height, waist and hip circumference; body mass index; blood pressure; LDL cholesterol were collected at the Oulu University Hospital.

Also, via echocardiograph, left atrium diameter, left ventricular mass and left ventricular mass index were measured at the hospital. Researchers used hospital and death registries to determine if a subject had been diagnosed with atrial fibrillation.

How it was done: The subjects included in the study completed and returned weekly food records and questionnaires regarding alcohol consumption, smoking, medications and medical history.

As part of the research, subjects’ blood was tested and they had regular echocardiographs. Subjects who did not accurately or completely fill out their food records were not included in the study, leaving  the data of 716 subjects (342 with hypertension and 374 without hypertension) for review.

Points to consider: Dietary sodium levels have previously been associated with stroke and other causes of death that are related to atrial fibrillation.

The authors noted that the number of atrial fibrillations experienced by the subjects might be higher than reported in the study, because only those events that needed emergency care were recorded.

The study did not include subjects whose dietary sodium intake could not be estimated. People who were excluded from the study were more likely to be diabetics; have higher BMI, larger waist circumferences and more smoking experience; be younger; consume more alcohol; and more likely to be on heart medication than the subjects included in the study. These factors make it likely that subjects with higher overall risk of cardiovascular problems were not part of the study, the authors wrote. “It is possible that if all subjects had been included in the present study, the association between sodium intake and new-onset [atrial fibrillation] could have been even stronger,” they reported.

Authors: Tero Juho Wilhelm Pääkkö, Juha S. Perkiömäki, Marja-Leena Silaste, Risto Bloigu, Heikki V. Huikuri, Y. Antero Kesäniemi & Olavi H. Ukkola

Published: Dietary sodium intake is associated with long-term risk of new-onset atrial fibrillation, Annals of Medicine, Nov. 23, 2018