Two types of omega-3s—eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)—are found in seafood and are sometimes referred to as long-chain omega-3s. Another type, alpha-linolenic acid (ALA), is found in certain plant oils such as flaxseed, soybean and canola oils, and can also be found in other foods of plant origin, such as chia seeds and black walnuts.
› Health Benefits
Omega-3s are used in several conditions of the circulatory system, as well as conditions affecting the brain, nervous system, mental health, eyes and other systems.
According to the 2012 National Health Interview Survey, fish oil supplements are the nonvitamin/nonmineral natural product most commonly taken by adults and children. For some health conditions, the evidence for benefits from seafood is stronger than the evidence for supplements.
Several studies have been evaluated showing that those who regularly eat seafood are less likely to die from heart disease than those who rarely or never eat it. Several analyses have shown that there is no evidence that omega-3s can reduce the risk of fatal or nonfatal coronary heart disease, and there is no evidence that they can reduce the risk of heart attacks or death from heart disease.
Eating seafood has been linked to a moderate reduction in the risk of stroke. According to a report from the Agency for Health Research and Quality (AHRQ), there is some evidence that omega-3s from marine sources may reduce the risk of one type of stroke, ischemic stroke, but they have not been shown to reduce total stroke or death from stroke.
Triglycerides are a type of fat found in the blood, which can raise the risk of heart disease at excessive levels. High doses of omega-3 fatty acids can reduce triglyceride levels. Several products containing omega-3s have been approved as prescription drugs to be used in combination with diet to reduce triglyceride levels in patients whose triglyceride levels are very high. The composition of these products is not the same as regular omega-3 supplements, so the effects of the prescription products may not be the same as the supplemental products.
Some studies have shown promising results, but it is still unclear whether omega-3s are helpful for depression. Omega-3s have not shown to be helpful with depression that occurs during pregnancy or after childbirth.
Attention-deficit hyperactivity disorder (ADHD)
Research has had conflicting results, so it is unclear whether omega-3s help with ADHD.
Alzheimer’s disease/cognitive impairment
Some research has shown that people who eat more seafood may have a reduced risk of cognitive decline. Supplements have not shown to help prevent cognitive impairment or Alzheimer’s disease, or to improve symptoms of these conditions. It is possible that omega-3s may have different effects in people who carry a gene called APOE4, which is associated with an increased risk of Alzheimer’s, and may benefit from taking DHA before developing signs of the disease.
Studies have found that omega-3 fatty acids decrease the inflammation that compromises thyroid function. Omega-3s may be particularly beneficial for people with Hashimoto’s thyroiditis, in which the immune system attacks the thyroid gland and causes inflammation. Omega-3 fats improve the integrity of cell membranes, helping to protect them from the damage of this disease.
Cortisol, a hormone released by the adrenals as a response to stress, normally acts as an anti-inflammatory, but will be unable to do so properly if the adrenal glands are overworked. Omega-3 acids can reduce inflammation in the body, which is helpful as the body’s reaction to stress tends to increase inflammatory processes.
Age-related macular degeneration (AMD)
This eye disease can cause vision loss in older people. Two major studies sponsored by the National Institutes of Health, Age-Related Eye Disease Study and Age-Related Eye Disease Study 2 (AREDS2), showed that dietary supplements containing specific combinations of vitamins, antioxidants and zinc helped slow the progression of AMD in people at high risk of developing the advanced stages of this disease. AREDS2 tested EPA and DHA, with results showing that the addition of these omega-3s didn’t provide any additional benefits.
Dry eye disease
Results of several small studies have suggested that omega-3 supplements may help relieve symptoms of dry eye disease. A 2018 study sponsored by NIH found that the supplement was no more helpful than a placebo. This study tested omega-3 supplements for a full year in a group of more than 500 people with moderate-to-severe dry eye disease.
The types of omega-3s in seafood and fish oil may be modestly helpful in relieving symptoms of rheumatoid arthritis and decreasing patients’ need for nonsteroidal anti-inflammatory drugs.
The nutritional value of seafood is important during early development. FDA guidelines recommend that pregnant or breastfeeding women eat at least 8 ounces but no more than 12 ounces of a variety of seafood each week, from choices low in methyl mercury. A study completed in 2016 evaluated giving omega-3s to pregnant or breastfeeding women or gave formulas with added DHA to infants. The results showed that when women took the supplement during pregnancy, their babies’ birth weight was slightly higher, but risk of undesirably low birth weight did not change. Pregnancies also lasted a little longer, but there was no effect on the risk of premature birth. The supplement was not found to have any effect on any aspect of the mothers’ or infants’ long-term development.
› How much do I need?
The dosage varies depending on age and what it is being used for. Be sure to follow relevant directions on product labels, and consult your pharmacist, physician or other healthcare professional before using.
Side effects from omega-3 supplements are usually mild and include an unpleasant taste, bad breath, bad-smelling sweat, headache, and gastrointestinal symptoms like heartburn, nausea and diarrhea.
Several studies have linked higher blood levels of long-chain omega-3s with higher risk of prostate cancer. Other research has shown that men who frequently eat seafood have lower prostate cancer death rates and that dietary intakes aren’t associated with prostate cancer risk.
› Dietary supplements
Omega-3s can be found in fish oil and fish liver oil supplements (EPA and DHA), krill oil (EPA and DHA), algal oils (DHA and sometimes EPA) and flaxseed oil (ALA).
Please consult your health care provider before making changes to your vitamin/supplement regimen.