Fish Oil Side Effects: What To Know About Boosting Your Omega-3 Intake With Supplements

Be honest: Do you really get in those two recommended servings of heart-healthy fatty fish per week? No judgment—most people don't! And that's just the foundational, baseline recommendation. The starting line, if you will. Even if you make it a habit to regularly top salads with tinned sardines or swap the usual beef for salmon burgers, there are still certain cases in which your doctor or nutritionist might recommend upping your omega-3 game (often with a supplement like fish oil) to make sure you're getting enough of these healthy fats in your system on the regular. If you know seafood isn't your jam, perhaps you've taken it upon yourself to add a supplement to your routine!

Another reason the omega-3s found in fish oil are so important, especially these days, is that the average American diet is (too) high in omega-6 fats, which have inflammatory properties. While omega-6s are found in healthy foods like pumpkin seeds, sunflower seeds, and walnuts, they're also found in high amounts in vegetable oils (aka soybean, corn, canola, etc.) and processed foods, Kelly explains. And when people eat lots of processed, vegetable-oil-containing foods, they consume too many omega-6s compared to omega-3s, which creates an omega fats imbalance and is counterproductive for omega-3s' anti-inflammatory actions.*

Just how many omega-3s you need—and thus how much fish oil would best support your health—depends on individual factors and health priorities. The Dietary Guidelines for Americans recommends adults get an average of 250 to 500 milligrams of EPA and DHA per day (that's about one to two servings of fish a week) for starters.

The American Heart Association echoes this two-fish-serving baseline and then recommends a higher daily dose of these marine omega-3s—1,000 milligrams per day—for optimizing heart health.*

Meanwhile, research1 indicates that pregnant women need 650 milligrams of omega-3s per day, with at least 300 milligrams of that coming from DHA (a must-have for baby's brain, eye, and neural development), specifically.*

Though research2 suggests that a teeny-tiny proportion of people (just about 1%) experience digestive upset after taking fish oil, it is a potential side effect those with sensitive stomachs might notice. This could be simply because fish oil is fat, which some people have trouble digesting. "Fat may relax the lower esophageal sphincter [a set of muscles at the bottom of the esophagus, near the entrance to the stomach] and promote acid reflux or slow the flow of digestion," explains dietitian Isa Kujawski, MPH, RDN.

If you have a bleeding disorder or take medications classified as blood thinners, out of an abundance of caution, Kelly recommends talking to your doctor about any supplements, including omega-3 fish oil supplements, you take (or are interested in taking), since they can have a blood-thinning effect at extremely high doses. Again, 10,000 milligrams of EPA plus DHA daily (that's 10 grams) has been shown to be safe according to research. The cautionary linking of fish oil to blood thinning started decades ago simply because of the way omega-3s interact with platelets3, which are cell fragments in the blood that play an integral role in clotting, Kujawski says.

Ferira says this potential side effect has been blown out of proportion. "Way too much of any good thing, even water, can have potentially negative effects on our health. But in this case, a textbook physiological mechanism, that omega-3s can impact platelets, has been used to broadly fearmonger against completely safe doses of omega-3s found in supplements." She goes on to say that, "In reality, the blood-thinning effect of fish oil actually occurs at absurdly high levels of EPA plus DHA, 10 grams plus, which by the way, no supplement even comes close to containing. Omega-3 supplements are playing in the 200- to 1,800-milligram range of EPA plus DHA 99% of the time."

There's conflicting science here, but some research does suggest that very high doses of omega-3 can affect blood sugar in some people, according to Kujawski. (Newer studies4 actively question this.) To be safe, she recommends checking in with your doctor if you have any blood sugar concerns.

Ferira shares that, "to be clear, omega-3 supplementation research has been shown to be highly effective for promoting a healthy profile of lipids, with particular benefit to triglyceride levels. That same research has found a modest beneficial trend for glucose, insulin, and HbA1c measures of glucose control5, while other studies have reached statistical significance, demonstrating omega-3s' ability to improve insulin sensitivity6."*

Though not a concern with the large majority of fish oil options (i.e., in gelcaps or softgels), "high doses of certain sources of omega-3s such as cod liver oil also contain high amounts of vitamin A," Kujawski explains.

While fish oil supplements' impact on blood pressure9 is exactly what makes them appealing to certain people, it may be a consideration for those who take blood pressure medications or who already have low blood pressure. So partner with a health care practitioner to be sure.

Research is quite limited here, with just individual case studies11 (i.e., one person) suggesting a link between taking high doses of omega-3s (specifically a very high-dose EPA supplement in this singular case12) and trouble sleeping—so Kujawski says that more scientific investigation is needed to better understand any potential relationship between high amounts of omega-3s and sleep.

One of the most well-known positives of omega-3s: cardiovascular health. In addition to promoting healthy blood circulation and pressure, these good-for-you fatty acids also support optimal levels of lipids, particularly triglycerides16 (a type of fat in the blood).*

Because of their (lesser-known) role in helping to regulate calcium absorption, omega-3s support bone health, studies17 indicate. Those anti-inflammatory properties also come in handy for supporting joint function and comfort18.*

The omega-3 DHA, in particular, is crucial for brain development19, as well as for supporting cognition20 (including things like memory and mood) throughout your lifetime.*

Ferira shares, "Indeed, these omega-3s are literally intrinsic to the cellular membranes of cells throughout our central nervous system, from our brain and retina to neurons throughout the body. They are ensuring healthy neuronal signaling via synaptic transmission, which translates practically into mental acuity, memory, vision, and more."*

More recently, science has started digging more into another exciting perk of omega-3s: Their role in mental well-being. Researchers are still exploring21 exactly how EPA and DHA (the two omegas being touted for their mood benefits) have a positive impact here, but there is certainly evidence to suggest they have an important part to play in supporting a balanced mood22.*

In addition to brain development, DHA is also a must-have for eye development early on and function throughout life. It both works to ensure that the retina functions23 as it should and helps the eyes combat oxidative stress24.*