DHA-rich fish oil increases the omega-3 index and slows the resting heart rate in healthy adults

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A daily DHA dose of 540 mg, equivalent to two servings of fish per week, was associated with a significant increase in the omega-3 index (EPA + DHA) from around 5.3% at the start of the study to over 7.5% after eight weeks . In contrast, the O3I did not change significantly for the control group.

“This current study showed that a small additional intake of fish oil leads to an increased O3I, which reflects the preferential incorporation of DHA into the myocardial membranes,” write researchers from the University of Wollongong in the Journal of the American College of Nutrition.

“In young and healthy adults who were free from cardiovascular disease, HR was dormant [heart rate] was slowed down, but no significant change in HRV [heart rate variability] Responsiveness was evident in either resting bradycardia or cardiovascular reflex challenges (parasympathetic or sympathetic dominant), meaning that it did not alter the homeostatic process that required rapid HR disturbances.

“This offers some support for the direct influence of long-chain ω-3 PUFA [omega-3 polyunsaturated fatty acids] on the intrinsic heart rate independent of the autonomic nervous system in this group of healthy adults. “

Cardiovascular health

The study complements a lot of evidence supporting the potential cardiovascular benefits of omega-3 fatty acids, first published by Dr Journal of Clinical Nutrition 1975.

To date, polyunsaturated fatty acids (PUFAs) have been linked to a range of cardiovascular benefits, from improving blood lipid levels to reducing the risk of thrombosis, and from improving blood pressure and heart rate to reducing the risk of coronary artery disease (CHD) ) and cardiac death.

Regardless of the results of the study, Harry Rice, PhD, VP of Regulatory & Scientific Affairs of the Global Organization for EPA and DHA Omega-3s (GOED) said, “Given the low baseline heart rate, the effect of the high” DHA fish oil supplement ( versus placebo) at resting heart rate was particularly impressive.

“Previous studies have shown positive associations between omega-3s and heart rate variability, so it seems strange that the current study did not show any benefit. At the same time, this can be for a number of reasons, including the small number of subjects, ”added Dr. Rice added.

Study details

For the new study, the Wollongong scientists recruited 20 young (average age 27) and healthy adults to take part in their study. The volunteers were randomly given eight weeks of control supplements (soybean oil) or DHA-rich tuna oil (containing 560 mg DHA per day and 140 mg EPA per day).

In addition to the increases in the omega-3 index, the researchers also found that whole blood levels of EPA and DHA in the DHA group increased significantly by an average of 2.05%. There were no significant changes in this measure in the control group.

Resting heart rate dropped an average of five beats per minute in the DHA group, the researchers reported.

“The increase in O3I in the fish oil group was associated with a slowdown in resting HR, similar to the effects seen in exercise,” they wrote. “This finding is in line with previous observations that have shown that fish oil supplementation slows resting HR in generally healthy but untrained people and in cardiac stress from exercise protocols.

“However… studies that show a slowed resting or training HR were predominantly supplemented with fish oil doses in the therapeutic range. [greater than 2 grams per day]. The effectiveness of the low-dose fish oil supplement in slowing resting HR in the current study may be due in part to its high DHA content, ”they added.

Contrary to the expectations of the researchers, there was no influence on the heart rate variability (HRV) in the study participants.

“Given that elevated resting HR and low blood levels of long-chain ω-3 PUFA (particularly DHA) are independently associated with an increased risk of sudden cardiac death, these results underscore the value of nutritional interventions aimed at fish or Fish oils, which contain DHA, even increase in healthy young adults and supports the recommendation to establish a reference intake through diet, ”the researchers conclude.

Source: Journal of the American College of Nutrition
Published online in advance, doi: 10.1080 / 07315724.2021.1953417
“DHA-rich fish oil increases the omega-3 index in healthy adults and slows the resting heart rate without changing the cardiac autonomic reflex modulation”
Authors: MJ Macartney et al.

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