Fish oil is one of the most popular supplements in America, boasting a booming, $1 billion business each year, according to Harvard Health Publishing. Cod liver oil is one particular type of fish oil that comes from the liver of cod fish and is high in healthy, polyunsaturated fats known as omega-3s and omega-6s, as well as in vitamins A and D. It's become especially trendy in recent months, but you may want to learn more about this supplement before buying a bottle.
"Cod liver oil is one of those supplements that’s been around for decades, and it’s still something I see people asking about in practice," shares physicianOlalekan Otulana, MBCHB. "It can be beneficial for certain people, but it’s not something I’d recommend across the board without a bit of thought behind it."
Ahead, learn from experts about the health benefits and potential risks of taking cod liver oil.
RELATED: 10 Surprising Benefits of Taking Fish Oil Every Day.
Benefit: Cod liver oil could help fight inflammation.
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Some studies have found that cod liver oil may help reduce inflammation. Specifically, the research shows that, in athletes, "regular use can help lower CRP levels—an indicator of inflammation—both at rest and after exercise," explains Jennifer Pallian, BSc, RD, a registered dietitian and food scientist.
"Also, people with rheumatoid arthritis have reported less joint pain, stiffness, and swelling after taking it regularly," Pallian notes. In fact, a 2008 study promoted cod liver oil as a drug-sparing agent in patients with rheumatoid arthritis.
Risk: Cod liver oil could lead to harmful levels of vitamins A or D.
ShutterstockCod liver oil contains vitamins A and D, nutrients that are essential for bone health, eye health, immunity, and more. However, it is possible to have too much of a good thing.
Otulana notes that vitamin A is fat soluble, "which means the body stores it, and taking too much over time can be harmful, particularly for the liver or during pregnancy."
"Too much vitamin A or D can be toxic and may raise the risk of asthma or high blood pressure during pregnancy," agrees Pallian. "In one study, women who consumed high amounts of cod liver oil early in pregnancy had a significantly higher risk (four times more likely) of developing hypertensive disorders."
A separate study found that the cod liver oil supplements with a high amount of vitamin A were "significantly" associated with a heightened risk of asthma in non-pregnant adults.
RELATED: 8 Surprising Vitamin D Side Effects, According to Doctors.
Benefit: Cod liver oil could improve heart health.
Doctors Discover Alarming Link Between Heart Health and Cognitive Decline: "Should be a Warning"iStockCatherine Hyatt, MD, medical content lead at Levity, says the heart health benefits are especially promising but notes that the FDA has not evaluated cod liver oil for medical use.
"There is some evidence that these may help lower blood pressure, which could improve heart health, although more extensive research is needed," she notes.
However, there is research to support the cardiovascular benefits of omega-3s, which cod liver oil is high in.
"This research found that omega-3 supplementation was associated with a 7 percent relative reduction in cardiovascular mortality and a 13 percent relative reduction in non-fatal heart attacks. They also had fewer heart disease events overall," Sarah Otto, co-founder and in-house nutritionist of Goodness Lover, previously shared with Best Life, though she, too, says more research is needed.
Risk: Cod liver oil can interact with other medications.
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It's always advisable to speak with your doctor before taking a new supplement to ensure it won't interact with any medications you're taking or might take. But in the case of cod liver oil, some of these interactions are widely documented.
"At higher doses, it can increase bleeding risk, especially when combined with blood thinners like warfarin or aspirin," warns Pallian.
She adds that cod liver oil may affect blood sugar levels and can therefore interact with diabetes drugs.
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Benefit: Cod liver oil may improve blood sugar control in those with gestational diabetes.
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Pallian points to several studies that suggest cod liver oil can have positive effects on those with gestational diabetes.
One 2019 study concluded that taking cod liver oil effectively reduced blood glucose levels, lipid levels, hs-CRP (a marker of liver inflammation), insulin resistance, and the incidence of perinatal complications.
Benefit: Cod liver oil could help with respiratory issues.
The Surprising Health Risks You Didn't Know AboutiStock"It's believed that cod liver oil supplementation can decrease upper respiratory tract infections in young children," shares Dana Zhao, MD, a New York-based gastroenterologist, referencing a 2010 study.
Pallian adds that cod liver oil "may also help with asthma control since higher omega-3 levels are linked to better symptom control and less reliance on medication."
RELATED: 5 Supplements That Can Damage Your Kidneys, Doctors Say.
7. Risk: More research is still needed on cod liver oil supplementation.
The Benefits of Cod Liver Oil—And Whether You Should Take It, Doctors SayShutterstockThe experts agree that while research suggests several health benefits of cod liver oil, there is still more work to be done.
"While there may be some evidence for using cod liver oil, the FDA has found this to be inconclusive," says Hyatt. "In general, a food-first approach is preferred over supplementation."
To her point, if you decide against taking cod liver oil, you can still get omega-3 fats from food sources such as fatty fish, eggs, nuts, seeds, and legumes.
"I always suggest checking the label, being mindful of how much you take and if in any doubt, discuss with your doctor or pharmacist before starting it regularly and using it sensibly rather than assuming more is better," concludes Otulana.
