Fish oil is an important natural remedy for high blood pressure. Fish oil is a rich source of two long-chain, omega-3 fatty acids, EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). These are extracted from the flesh of oily fish such as salmon, herrings, sardines, pilchards and mackerel and are derived from the micro-algae on which the fish feed. Similar oils are derived from cod liver oil, which is also rich in vitamins A and D. For vegetarians algae oils are a good source of DHA, and DHA appears to provide the best protection against high blood pressure.
Fish oil and high blood pressure
Omega-3s are converted in the body to substances (series 3 prostaglandins and series 5 leukotrienes) that reduce inflammation. This helps to balance the effect of dietary omega-6 fats (mostly derived from vegetables oils such as safflower and corn oils) which promote inflammation. A diet that provides good amounts of omega-3s reduces the production of inflammatory mediators that would otherwise increase blood stickiness and hasten both hardening and furring up of the arteries and the progression of hypertension.
Results from 70 clinical trials have shown that, compared with placebo, daily EPA+DHA intakes reduce blood pressure, on average by 1.52/0.99 mmHg in all people – whether or not you have hypertension. When just those with untreated hypertension were assessed, their blood pressure fell by an average of 4.51/3.05 mmHg. The researchers concluded that all doses of omega-3 fish oils can lower systolic blood pressure (the upper reading) but that doses of at least 2 grams, or more, are needed to reduce diastolic blood pressure (the lower reading).
DHA seems to be especially important for regulating blood pressure and supplements offer the greatest protection. When over 56,200 adults were followed for up to 20 years, those who at the most fish were only 4% less likely to develop high blood pressure, but when circulating omega-3s were measured, those with high levels (from supplements) were 33% less likely to develop high blood pressure than those with low levels, and when circulating levels of DHA were assessed, the risk of developing high blood pressure was 36% lower. The researchers suggested that increasing intakes of DHA may help to prevent high blood pressure.
Fish oil and heart disease
Even modest increases in the amount of oily fish you eat have a protective effect against heart attacks. If you’ve already had a heart attack, then eating more fish significantly reduces the chance of a second one occurring and, if it does, the chances of dying as a result are significantly decreased. Fish oil polyunsaturated fatty acids appear to protect against abnormal heart rhythms, especially in heart muscle receiving a poor blood supply (ischaemia).
Fish oil and stroke
Results from as many as 38 studies, involving over 794,000 people, showed that those who ate two to four servings of fish a week were 6% less likely to experience a stroke than those eating less than one serving of fish a week. Those who ate five or more servings of fish per week were 12% less likely to experience a stroke. Results were broadly similar for fish and omega-3 supplements.
Diet should always come first, but not everyone likes fish enough to eat five portions a week. This is where supplements come in to their own.
The usual dose for omega-3 fish oils is between 1g to 3g a day. Higher doses may be recommended under medical supervision, for example to lower a raised triglyceride level, or to treat severe inflammatory diseases.
A recent study suggested that supplements providing 0.7g EPA + DHA daily could produce similar results to a higher dose of 1.8g EPA + DHA per day, for eight weeks, with systolic blood pressure reducing by an average of 5 mmHg.
Typically a 1g capsule of high-strength fish oil contains around 500mg of the important long-chain omega-3 fatty acids, EPA and DHA, but check label claims to find which are the most cost-effective.
Select pharmaceutical grade omega-3 fish oil supplements to ensure they are virtually free from marine pollutants.
If you prefer to take cod liver oil, which as the name suggests is extracted from the liver of cod rather than from oily fish, doses are lower due to their high vitamin A content. A typical dose for cod liver oil is between 1g and 1.5g per day.
If you are also taking a multivitamin, check the total amount of vitamin A you are taking does not exceed recommended doses. Vitamin A is best limited to less than 5,000 IU (1,500 mcg) per day although intakes of up to 10,000 IU (3,000 mcg) are considered safe.
Fish oil safety
Cod liver oil should not be taken during pregnancy as excess vitamin A may be harmful to a developing baby.
Although fish oils were originally thought to increase blood sugar levels in people with diabetes, several large-scale analyses have now concluded that fish oil supplements do not have a significant effect on glucose control. As always, if you have diabetes, monitor your blood sugars carefully when starting to take any supplement, including fish oil, as some people respond differently.
Because of their blood thinning effect, people with clotting disorders or on blood-thinning medication should only take an omega-3 fish oil supplement under the advice and supervision of their doctor.
Fish oils may worsen asthma in people who are also sensitive to aspirin.
If your blood pressure is borderline or raised, self-monitoring is key to maintaining good control.
Click here for advice on choosing a blood pressure monitor to use at home.
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