Omega-3 fatty acids are a type of fat found in the human body, foods, and dietary supplements. Seafood, as well as fish and krill oil supplements, is rich in long-chain omega-3s such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Plant oils and plant-oil supplements—such as those derived from flaxseed, soybean, canola, chia seeds, and black walnuts—are abundant in another type of omega-3 fatty acid called alpha-linolenic acid (ALA).
Much research has been done on the health effects of omega-3s, particularly fish-derived EPA and DHA. However, this research has often yielded mixed results, leaving clinicians uncertain whether omega-3s have any health benefits. Nevertheless, fish oil/omega-3 supplements are the most popular nonvitamin and nonmineral products among American adults, with 7.8% of the population taking them.
Let’s take a closer look at some of the potential health benefits that omega-3s may offer, according to recent research.
In a 2011 meta-analysis involving 17 studies, researchers found that people who ate seafood 1-4 times weekly demonstrated a lower risk of heart disease mortality compared with those who did not regularly consume seafood.
However, investigators who conducted a meta-analysis of 98 studies in 2016, which was supported by the US government, noted that omega-3 intake either via diet or supplementation yielded no benefit with respect to heart attack or cardiac death.
In addition, according to results of a 2018 high-power meta-analysis of 10 studies (n=77,917), omega-3 supplements exerted no effect on fatal or non-fatal coronary artery disease.
Although investigators of pre-2012 studies have demonstrated the cardioprotective benefits of omega-3 consumption, post-2012 research has not reflected such benefits. This phenomenon could be due to two things. First, the plethora of public health messages promoting seafood consumption may have encouraged people to consume more seafood in their diets, with any additional supplementation yielding no benefit. Second, more people are taking statins, the benefit of which likely dwarfs any benefit derived from dietary omega-3s.
Nevertheless, the consumption of seafood has been tied to a moderate decrease in stroke risk. Other research has linked the consumption of omega-3s from marine sources, such as fish oils, to decreased risk of ischemic stroke—but not to decreased risk of total strokes or death from stroke.
High levels of omega-3s via prescription supplements have been shown to decrease very high triglyceride levels, in combination with dietary changes. It has yet to be established, however, whether over-the-counter omega-3 supplements proffer the same benefit.
• Depression. The effect of omega-3s on depression is unclear, with conflicting results regarding benefits among studies. Moreover, some researchers have suggested that, even if omega-3s do exert clinical benefits with respect to depression, the effects are small. Interestingly, EPA may be better at helping with depression symptoms than DHA, and EPA supplementation could complement the use of antidepressants.
• Alzheimer’s disease. According to limited research, omega-3s may help prevent cognitive decline, but omega-3 supplements have not specifically been shown to decrease the risk or improve the symptoms of Alzheimer’s disease. Of note, it’s possible that people with the APOE4 gene—which confers a greater risk of Alzheimer’s disease—may experience protective effects by taking DHA before disease onset.
• Dry eye disease. According to results from several smaller studies, omega-3 supplements may help relieve the symptoms of dry eye disease. Then again, in a high-power, prospective, National Institutes of Health-sponsored study published in 2018, researchers found that omega-3 supplements didn’t help with moderate-to-severe dry eye disease.
• Rheumatoid arthritis. Omega-3s found in seafood and fish oil may offer some benefit in those with rheumatoid arthritis by relieving some symptoms and decreasing the need for nonsteroidal anti-inflammatory drugs.
Omega-3s have been studied in various other disorders with conflicting or inconclusive results, including attention-deficit/hyperactivity disorder, autism spectrum disorder, mental health disorders, multiple sclerosis, and age-related macular degeneration.
Adverse effects of omega-3s
Typically, the adverse effects of omega-3s are minimal and limited to headache, gastrointestinal upset, bad taste, bad breath, and pungent body odor.
However, several studies have been done to examine the link between long-chain fatty acids and prostate cancer, with mixed results. In some studies, omega-3 consumption was associated with an increased risk of prostate cancer.
It’s also important to note that omega-3 supplements may interfere with the action of anticoagulant medications. In addition, it’s unclear whether people who are allergic to fish may safely tolerate fish oil supplements.