NEW YORK—Docosahexaenoic acid is the fish oil of choice for reducing blood pressure and improving cardiovascular risk profiles.
So, why is everybody selling the other stuff—eicosapentaenoic acid (EPA)—as a dietary supplement?
It’s a good question with no simple answer.
But a direct comparison between the two key omega-3-fatty acids shows clearly that when it comes to controlling blood pressure, docosahexaenoic acid (DHA) is the King Salmon of fish oils, said Dr. Lawrence J. Beilin, at a conference sponsored by the American Society of Hypertension.
Dr. Beilin, a leading researcher in dietary and lifestyle interventions for cardiovascular disease, and his colleagues at the West Australia Heart Research Institute, Perth, randomized 59 mildly dyslipidemic, overweight but normotensive men to six weeks of supplementation with daily EPA, DHA, or olive oil in capsule form.
The subjects, who had a mean age of 48, took one 4 g capsule of oil per day, while continuing in their habitual diets. The investigators measured 24-hour blood pressures and heart rates.
The olive oil, acting as a placebo control, had no effect on 24-hour mean blood pressure. Relative to the subjects on olive oil, those on EPA had a mean change of –2.4 mmHg systolic and –1.3 mmHg diastolic, which was not statistically significant. Those taking DHA had larger mean pressure change of –5.5 mmHg systolic over –3.2 mmHg diastolic, and this difference was statistically significant.
The DHA patients had a 3.5 beat-per-minute reduction in 24-hour mean heart rate, a 3.7 bpm reduction in awake heart rate, and a 2.8 bpm drop in sleeping heart rate. EPA had no significant effect on any heart rate parameters.
How fish oils do what they do in the cardiovascular system is still somewhat mysterious. Dr. Beilin believes they may reduce thromboxane generation, inhibit vessel reactivity to vasoconstrictive signals, and concurrently increase responsiveness to vasodilatory mediators.
The Australian investigators plan to repeat their experiment but with hypertensive instead of normotensive subjects, both to test whether the fish oil effect is therapeutic, and to confirm that DHA is the key, as suggested by the first trial.
The problem is, purified DHA is difficult to obtain. The vast majority of fish oil supplements on retail shelves contain primarily EPA. And this means patients who routinely take the EPA supplements probably will not experience the cardiovascular benefits they hope to obtain.
Until the supplements industry gets on the ball, there’s always fish itself, for those patients who like it.
In an earlier study of hypertensive subjects, Dr. Beilin and his team showed one fish meal daily, including 100 g of a high-oil content ocean fish such as Atlantic salmon, could knock 6 mmHg off the systolic pressure and 3 mmHg off the diastolic, independent of any other interventions. But you need between 2 and 4 weeks of daily fish consumption to see a cardiovascular effect.
The amount of omega-3 fatty acid per serving varies considerably with the fish species and geography. Fish themselves get the omega-3s ultimately from plankton, and generally speaking, the colder the water, the higher the omega-3 content. One hundred grams of free-swimming Atlantic salmon contains 3–4 grams of omega-3-fatty acids, 40%–50% of which is DHA. Tuna and sardines are also DHA-rich species.
THE REDUX: Randomized study of 59 patients shows fish-derived omega-3 fatty acid supplements, 4 g/day, can reduce BP by as much as 5.5/3.2 mmHg. DHA, though harder to find in supplement form, was superior to the more common EPA in lowering pressure and heart rate; patients taking EPA supplements may not get the expected fish-oil CV benefits.
