Hypertension and Essential Fatty Acids

Fish oil is recommended for a number of cardiovascular conditions, including congestive heart failure (CHF) and heart attacks. It appears that fish oil may also help treat hypertension.

Fish oil has a number of effects on the cardiovascular system. It may help lower blood pressure by acting as a blood thinner and slightly reducing the heart rate, among other actions.

Read more details about Essential Fatty Acids.

Although the research record is mixed,^{15-21,104,137} it appears that fish oil may reduce blood pressure at least slightly.⁵⁶ Fish oil contains two major active ingredients, DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid). A 6-week, double-blind, placebo-controlled study of 59 overweight men suggests that the DHA in fish oil, but not the EPA, is responsible for this benefit.⁵⁷

Typical dosages of fish oil are 3 g to 9 g daily, but this is not the upper limit. In one study, participants ingested 60 g daily.

The most important omega-3 fatty acids found in fish oil are called eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In order to match the dosage used in several major studies, you should take enough fish oil to supply about 2 g to 3 g of EPA (2,000 mg to 3,500 mg) and about 1.0 g to 2.5 g of DHA daily (1,000 mg to 2,500 mg). Far higher doses have been used in some studies; conversely, one study found blood-pressure lowering effects with a very low daily dosage of DHA—0.7 g.²³⁸

DHA and EPA are not identical and might not have identical effects. Some evidence hints that DHA may be more effective than EPA for thinning the blood 176 and reducing blood pressure.¹⁰⁵ The reverse may be true for reducing triglyceride levels, but study results are conflicting.^160-165,235

Some manufacturers add vitamin E to fish oil capsules to keep the oil from becoming rancid. Another method is to remove all the oxygen from the capsule.

If possible, purchase fish oil products certified as free of significant levels of mercury, toxic organochlorines, and PCBs (see Safety Issues).

Flaxseed oil also contains omega-3 fatty acids, although of a different kind. It has been suggested as a less smelly substitute for fish oil. However, it is far from clear whether flaxseed oil is therapeutically equivalent to fish oil.^1,200

• Clinical nutritionist or registered dietitian
• Integrative MD
• Naturopathic doctor

Safety Issues

Fish oil appears to be generally safe. The most common problem is fishy burps. However, there are some safety concerns to consider.

For example, it has been suggested that some fish oil products contain excessive levels of toxic substances such as organochlorines and PCBs. ¹ If possible, try to purchase fish oil products certified not to contain significant levels of these contaminants. Note:Various types of fish contain mercury, but this has not been a problem with fish oil supplements, according to reports on Consumerlab.com.

Fish oil has a mild blood-thinning effect; ² in one case report, it increased the effect of the blood-thinning medication warfarin (Coumadin). ³ Fish oil does not seem to cause bleeding problems when it is taken by itself ⁴ or with aspirin. ⁵ Nonetheless, people who are at risk of bleeding complications for any reason should consult a physician before taking fish oil.

Fish oil does not appear to raise blood sugar levels in people with diabetes. ⁶ Nonetheless, if you have diabetes, you should not take any supplement except on the advice of a physician.

Fish oil may modestly increase weight and lower total cholesterol and HDL (“good”) cholesterol levels. ⁷ It may also raise the level of LDL ("bad") cholesterol; however, this effect may be short-lived. ⁸ If you decide to use cod liver oil as your fish oil supplement, make sure you do not exceed the safe maximum intake of vitamin A and vitamin D . These vitamins are fat soluble, which means that excess amounts tend to build up in your body, possibly reaching toxic levels. The official maximum daily intake of vitamin A is 3,000 mcg for pregnant women as well as other adults. Look at the bottle label to determine how much vitamin A you are receiving. (It is less likely that you will get enough vitamin D to produce toxic effects.)

Interactions You Should Know About

If you are taking warfarin (Coumadin) or heparin , do not take fish oil except on the advice of a physician.

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