Fish oil contains omega-3 fatty acids, types of fat important for certain body processes. Omega-3 fatty acids may help reduce a person’s blood pressure. However, their effect on cholesterol is controversial.

The three main types of omega-3 fatty acids are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Fish oil contains EPA and DHA.

Although the body can make very small amounts of DHA and EPA from ALA, it’s important to take in DHA and EPA through food and/or supplementation.

Read on to learn more about the effects of fish oil on cholesterol and blood pressure, how much to consume, and other health benefits.

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Cholesterol is a fatty substance in a person’s blood. The liver makes all of the cholesterol the body needs to build new cells and create certain hormones. However, people ingest additional cholesterol by eating foods from animals.

Cholesterol moves through the body in lipoproteins. There are many types of lipoproteins, but the two main types are:

Low-density lipoprotein (LDL): LDL is “bad” cholesterol. If a person has too much LDL in their blood, it can build up on the walls of their arteries. This buildup can lead to problems, such as a heart attack or stroke.

High-density lipoprotein (HDL): HDL is “good” cholesterol. It helps move LDL cholesterol from the arteries to the liver, which removes it from the body.

Triglycerides are another type of fat in the blood the body uses for energy. Having a combination of low HDL, high LDL, and high triglycerides can increase a person’s chances of a heart attack and stroke.

Learn more about the causes of high cholesterol here.

Hypertension, or high blood pressure, occurs when a person’s blood pressure is consistently higher than normal. This means their heart has to work harder to pump blood around their body.

If a person has high blood pressure, they have an increased risk of conditions, such as:

Learn more about high blood pressure here.

The effect of fish oil on cholesterol is controversial.

Older information from the journal American Family Physician notes that omega-3 fatty acid supplements could reduce triglyceride levels in a person’s blood. However, the authors note that omega-3 fatty acids may also increase a person’s LDL levels.

In contrast, research from 2021 found an association between increases in blood DHA and a reduction in LDL levels. Additionally, researchers found that fish oil supplements did not increase LDL levels.

However, this study mostly involves males with normal blood lipid levels. Further research is necessary to confirm these findings.

Another study from 2021 looked at the effects of combining cod liver oil supplements with the cholesterol-reducing medication rosuvastatin. People who took a combination of cod liver oil and rosuvastatin had a bigger reduction in cholesterol than people who only took rosuvastatin.

Research from 2017 states that eating fresh fish is better at reducing cholesterol than fish oil supplements. Researchers found that people who ate 250 grams (g) of farmed trout twice a week for lunch and dinner for 2 months had:

  • a reduction in LDL levels
  • an increase in HDL levels
  • a reduction in triglyceride levels
  • a reduction in total cholesterol levels

Researchers also found that people who took 2 g of an omega-3 supplement daily saw an increase in their LDL levels after 2 months.

What does the American Heart Association recommend?

The American Heart Association (AHA) recommends taking prescription omega-3 to help lower very high triglycerides greater than or equal to 500 milligrams per deciliter (mg/dl). People can take 4 g per day of EPA plus DHA or EPA only, either on its own or with cholesterol medication.

A person with high cholesterol should speak with a doctor before they begin taking supplements or modifying their diet. Supplements are not suitable as replacements for prescription medications.

The AHA suggests that 3 g of omega-3 daily may reduce a person’s blood pressure.

A 2022 meta-analysis concluded that people consuming 2–3 g per day of EPA plus DHA had an average reduction in their systolic and diastolic blood pressure of about 2 millimeters of mercury (mm Hg).

The AHA also found that people with hypertension had a greater reduction in blood pressure when taking omega-3 than people with normal blood pressure.

Learn about natural ways to lower blood pressure here.

Fish and other seafood contain fish oil. The amount of omega-3 can vary depending on the type of fish.

Cold-water fatty fish contain high amounts of omega-3. These fish include:

  • salmon
  • mackerel
  • tuna
  • herring
  • sardines

Fish with lower fat content, such as cod, tilapia, and shellfish, have lower levels of omega-3 fatty acids.

Certain foods may contain added omega-3, such as:

  • yogurt
  • milk
  • soy beverages
  • juices

Plant oils contain ALA, another form of omega-3 fatty acid. ALA is present in:

Walnuts and chia seeds are also good sources of ALA.

However, a 2019 article suggests that the body is only able to convert around 5–8% of ALA into EPA, suggesting that other sources may be more beneficial.

A person can consume fish oil via the food they eat or in supplement form.

The National Institutes of Health (NIH) recommends consuming 1.1–1.6 g of omega-3 per day. The AHA suggests that people should eat two servings of 3–4 ounces of fish per week.

Fish oil supplements generally contain 300 milligrams (mg) per capsule. However, the amount of omega-3 contained within fish or supplements can vary.

Learn more about eating fish for health here.

There is no recommended upper limit for omega-3 intake. However, according to the NIH, taking 900 mg of EPA and 600 mg of DHA daily for several weeks can reduce a person’s immune function.

Additionally, taking 2–15 g of EPA or EPA plus DHA daily may increase a person’s bleeding time. However, a 5 g combined daily dose of EPA and DHA is a safe amount to take over a long period.

Furthermore, people with cardiovascular disease (CVD), or those at risk of CVD, may have a slightly increased risk of an irregular heartbeat after taking 4 g of omega-3 supplements daily over several years.

Fish oil may have other health benefits, including:

  • lowering the risk of death from heart disease for people who eat seafood at least once a week
  • a moderate reduction in risk of an ischemic stroke in people who eat fish
  • relief from rheumatoid arthritis symptoms for people taking fish oil supplements

Learn more about the health benefits of fish oils here.

Side effects from taking omega-3 supplements are generally mild and can include:

Learn more about the possible side effects of fish oil here.

Omega-3 supplements may interact with certain medications. High doses of omega-3 supplements may cause bleeding when taken with anticoagulant medications, such as warfarin.

If a person is taking other medications, they should speak with a doctor before taking omega-3 supplements.

If people want to reduce their cholesterol and blood pressure levels, they may benefit from eating the following foods:

A person may also benefit from reducing their salt and alcohol intake.

Learn about 15 foods that lower cholesterol here.

Treatments for high cholesterol and blood pressure include lifestyle changes and medications. The AHA notes that having a healthy lifestyle can:

  • reduce high cholesterol and blood pressure
  • prevent or delay high blood pressure development
  • enhance blood pressure medication effectiveness
  • lower the risk of a heart attack, stroke, heart failure, kidney damage, vision loss, and sexual dysfunction

A person at risk of high cholesterol or blood pressure should try to maintain a healthy lifestyle. This can include:

Learn about natural ways to reduce cholesterol without medication.

Fish oils contain omega-3 fatty acids, which may be able to reduce a person’s blood pressure. However, their effect on cholesterol levels is controversial.

Omega-3 fatty acids are present in fish and seafood, plant oils, and fortified foods. The American Heart Association recommends a person eat two portions of fish per week.

Fish oil may also benefit other health conditions, such as rheumatoid arthritis. It generally has mild side effects, although high amounts may cause issues, such as bleeding.

A person with high cholesterol or blood pressure should speak with a doctor before they begin taking supplements or changing their diet.