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22-06-2010 | Article

Mediterranean diet linked to increased heart rate variability

Abstract

Free abstract

MedWire News: The consumption of a Mediterranean-style diet is associated with increased heart rate variability (HRV), a measure of good autonomic cardiac function, US researchers report.

They also note that this association is independent of genes, shared environmental factors, and known cardiovascular risk factors.

“This means that whether or not a person has an adverse genetic background or other risk factors for cardiovascular disease, this person would be likely to have better cardiac autonomic function if he or she follows a diet similar to the Mediterranean diet,” say Jun Dai (Indiana University) and colleagues in the journal Circulation: Cardiovascular Quality and Outcomes.

Dai et al investigated the dietary patterns of 276 monozygotic (MZ) and dizygotic (DZ) male twins raised together, with a mean age of 55 years.

Twin pairs were counted as individual patients, to aid the team’s identification of the degree of genetic influence on HRV.

As DZ twins share on average 50% identical genes, if the association between the Mediterranean diet and HRV was seen in DZ twins but not MZ twins it would suggest that genetic factors are potentially confounding the association.

Each twin pair completed the Willett Food Frequency Questionnaire over a 12-month period. A scoring system allocating a numerical value reflecting the level of correlation of each patient’s diet with the Mediterranean diet was devised.

In this system, a score of 1 was assigned to the high consumption (above the median) of desirable Mediterranean diet components, including vegetables, fruits, fish, and a high ratio of monounsaturated fatty acids to saturated fatty acids; and to the low consumption (below the median) of undesirable components, including dairy and meat. The higher the final score, the greater the similarity between the patient’s diet and a Mediterranean diet.

All the patients underwent 24-hour ambulatory electrocardiogram (ECG) recording to assess their HRV.

After adjusting for cardiovascular risk factors, such as hypertension and smoking, the findings revealed that men with high dietary scores had a greater heart beat to beat time interval variation, compared with those with low dietary scores (p<0.05). Specifically, patients in the top dietary score quartile (6–9 points) had a 10% to 58% increased HRV compared to those in the lowest quartile (0–3 points).

Based on mortality studies, the researchers estimate that this HRV increase is equivalent to a 9% to 14% reduction in cardiac mortality.

The researchers also found that the association between the Mediterranean diet score and HRV was more pronounced in DZ than MZ, twins, indicating some confounding by genetic factors. But the researchers note that genetic confounding was only significant for low frequency and the overall association between Mediterranean diet score and HRV remained after controlling for shared genes.

They conclude: “Our findings suggest that autonomic tone may be one of [the] mechanisms linking the Mediterranean diet to a lower rate of cardiovascular events.”

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Lauretta Ihonor