Omega-3: What it can and can't do for health

Omega-3 fatty acidsTrusted Source are a type of polyunsaturated fat — also referred to as “healthy fats” — praised for their potential protective roles in several chronic diseases, such as heart disease and dementia.

They are one of the key building blocks for cell membranes and remain a subject of interest in the scientific community.

The family of omega-3 fatty acids includes:

• alpha-linolenic acid (ALA)
• stearidonic acid (SDA)
• eicosapentaenoic acid (EPA)
• docosapentaenoic acid (DPA)
• docosahexaenoic acid (DHA)

DHA and EPA are the primary polyunsaturated fats in brain cell membranes and have been popularized and successfully marketedTrusted Source as dietary supplements.

Omega-3 fatty acids are essential, meaning the human body is incapable of creating them on its own — the fatty acids or their precursors must be obtained from the diet.

For instance, ALA from plant seeds can be converted in the body to all the other types of omega-3 fats: EPA, SDA, DHA, DPA.

However, this conversion is quite inefficientTrusted Source, with rates of less than 3% of ALA being converted to DHA or EPA in males and less than 10% in females — warranting adequate dietary intakes of DHA and EPA themselves.

Omega-3 in the diet

DHA, EPA, and DPA omega-3 fatty acids are synthesized by marine organisms such as algae and phytoplankton.

When consumed by fish, aquatic mammals, and crustaceans, the fatty acids enter the food chain and are stored in body fat, liver, and blubber. They are then later consumed by humans.

Food sources of DHA, EPA, and DPA include:

• fatty fishTrusted Source, such as salmon, sardines, mackerel, menhaden, or herring
• the liver of lean, white fish, such as halibut or cod
• blubber from seals or whales
• fish oilsTrusted Source from cod flesh, tuna, haddock, flounder, or krill oil

ALA, on the other hand, is concentrated in plant sources and is the most frequent omega-3 fatty acid used by the body to create all other types of omega-3 fatty acids.

Sources of ALA include nuts and seeds, such as flaxseed, chia seeds, and walnuts as well as oils, such as echium seed oil, canola, and soybean oils.

According to the National Institutes of Health (NIH)Trusted Source, most adults in the United States consume the recommended amount of omega-3 — 1.1 grams (g) for adult females and 1.6 g for adult males — in the form of ALA.

However, given that the conversion of ALA to DHA and EPA is poorTrusted Source, dietary intake of a combination of foods rich in ALA, EPA, and DHA is recommendedTrusted Source.

Furthermore, a myriad of DHA and EPA omega-3 supplements are available and contribute significantly to daily omega-3 intake. Fish oil is the most commonTrusted Source

 omega-3 supplement used by adults and children.

Omega-3 fats: What they can do for health

Decades of research on the health impacts of omega-3 fatty acids have provided controversial findings. Here are some evidence-backed benefits of consuming omega-3 fatty acids.

Anti-inflammatory properties

Chronic inflammationTrusted Source — also called low-grade inflammation — is linked to the development of obesityTrusted Source, heart disease, and cancers.

Omega-3 fatty acids have been shown to exert anti-inflammatoryTrusted Source effects in the human body and may aid in lowering markers of inflammation, such as C-reactive protein and interleukin-6.

In fact, omega-3 fatty acids are regarded as one of the most potentTrusted Source lipids capable of reducing oxidative stress and inflammation. It also potentially guards against the development of chronic diseases.

Lower cholesterol

In a 6-week studyTrusted Source, daily supplementation with at least 1.2 g of DHA significantly reduced triglyceride levels and increased “good” cholesterol, or high-density lipoprotein.

In addition, omega-3 fatty acids lowered the “bad” cholesterol, low-density lipoproteins (LDL), when dietary saturated fats were replaced with polyunsaturatedTrusted Source and monounsaturated fatty acids found in plants foods such as nuts and avocados.

Elevated triglycerides and LDL cholesterol are linked to an increased risk for metabolic syndromeTrusted Source and heart diseaseTrusted Source.

However, a recent evidence-based practice summaryTrusted Source has shown no impact on a range of cardiovascular disease (CVD) outcomes from the use of omega-3 fatty acid supplements in patients with established CVD or raised risk factors for CVD.

Lower blood pressure

On the other hand, omega-3 fatty acids have been shown to improve vascular health — the health of the blood vessels — by increasing the bioavailability of nitric oxide.

In a phase 2 scientific study, nitric oxideTrusted Source induced dilation (relaxation) of the blood vessels and led to a significant reduction in blood pressure.

May reduce the risk of heart disease

By reducing markers associated with an increased risk of developing heart disease — high triglycerides, cholesterol, and blood pressure — omega-3 fatty acids may reduce the risk of heart disease, according to a reviewTrusted Source analyzing existing studies.

The same review concluded that high-dose daily supplementation with 4 g of purified EPA in people with elevated triglycerides levels led to a 25% reduction in cardiovascular events.

In their 2018 reviewTrusted Source, Prof. Fereidoon Shahidi, professor of biochemistry at Memorial University, Canada, and Prof. Priyatharini Ambigaipalan, currently at the School of Science and Engineering Technology at Durham College, also in Canada, identified evidence of health benefits from omega-3 in noncardiovascular health conditions.

Improve tolerance to cancer treatment

Omega-3 fatty acids may improve the efficacy and tolerance of chemotherapy and is a potential supportive treatment to people undergoing cancer treatment.

More specifically, daily supplementation with EPA and DHA helped patients with head and neck cancers and breast cancerTrusted Source to maintain body weight and reduce cancer-related muscle loss.

Improves depression

A 2019 review studyTrusted Source of over 2,000 participants showed a beneficial impact of EPA omega-3 fatty acids on depression, with DHA showing little benefits.

This finding is supported by other studies included in Prof. Shahidi’s and Prof. Ambigaipalan’s review, indicating that fish oil supplementation helps protect against major depressive disorder in people between the ages of 15 and 25 years.

Furthermore, moderate intakes of fatty fish and seafood were associated with fewer occurrences of depression.

Omega-3 fats: What they cannot do for health

Omega-3 fatty acids have been successfully marketed as heart-friendly and reported to reduce the risk of adverse heart disease-related outcomes.

However, its role and health benefits for some conditions have been challenged and discredited. This Cochrane report review found no evidence of the benefit of omega-3 supplements on heart disease, stroke, or death.

Here are some conditions that omega-3 fatty acids may not prevent or improve, based on the latest scientific evidence.

Reduce risk of death by heart disease

Prof. Shahidi and Prof. Ambigaipalan also found that the consumption of omega-3 fatty acids does not reduce the risk of adverse heart disease-related outcomes, such as sudden cardiac death, heart attack, or stroke, even in individuals without a history of disease.

Although omega-3 fats lower the risk of developing heart disease by lowering triglyceride, the “bad” cholesterol LDL, and blood pressure, a meta-analysis of over 80,000 individuals found that their supplementation neitherTrusted Source prevented death from all causes nor heart disease.

Prevent blood clots

Anti-clotting effects of omega-3 fatty acids have been proposed by reducing platelet aggregation. However, this finding has been controversial, and the evidence in this regard is weakTrusted Source — typical doses of omega-3 fats from foods and supplements have a mild effect.

Prevent or treat diabetes

EvidenceTrusted Source suggests that increasing omega-3 intake does not prevent or treat diabetes.

It does not affect fasting blood sugar, insulin resistance, or glycosylated hemoglobin in those with type 2 diabetes and metabolic syndrome.

Prevent cancer

Omega-3 fatty acids have been reported to reduceTrusted Source the complications of some cancer patients, and early findings look promising. However, there is no evidence of any action of omega-3s preventing the development of cancers.

In a meta-analysis of over one million people, a particularly high intake of omega-3 fats — 5–15 g per day — did not significantly reduce lung cancer risk, and in some cases, increasedTrusted Source the risk of developing lung cancer.

Therefore, too low or too high omega-3 intake may be harmful.

Source: Medical News Today