Cod liver oil has been around far before taking fish oil supplements became trendy. Though it doesn’t deliver the same concentrated dose of EPA and DHA that you’d get from a fish oil capsule, cod liver oil has some alternative benefits in its high levels of both vitamin D and vitamin A. Here’s the run-down on the science behind cod liver oil’s heart and metabolic health benefits.
Research
Cod liver oil benefits
1. Cod liver oil was the original fish oil supplement
While recently, omega 3 fatty acids from fish oil in general have become very popular in their own right, cod liver oil popular far before fish oil or krill oil supplements.
Touted as beneficial to your health for decades, it’s now being used to reduce risk factors for chronic disease and fight inflammation.
Since the cod is, after all, a fish, you can expect many of the same benefits as fish oil. What distinguishes cod liver oil is its tendency to have much higher contents of vitamin A and vitamin D.
If you prefer to get your vitamins and minerals from natural sources, the vitamin D will be of particular interest: aside from certain kinds of mushrooms, there are very few other dietary sources of vitamin D (1).
2. Cod liver oil might help prevent heart disease
Early research in animals found that cod liver oil could help control and even prevent heart disease. A study published in 1986 in the New England Journal of Medicine used a small group of pigs with high levels of blood lipids, which are known to contribute to artery hardening and heart disease.
About half the pigs were fed a cod liver oil supplement for eight months (2). The other half of the pigs were not fed any special supplement, and the hogs were given a diet that was intended to induced heart disease.
The researchers found that the cod liver oil supplement substantially reduced markers of heart disease in the pigs when compared to the control group, and they hypothesized that this happened because the cod liver oil modified the way the pigs’ bodies metabolized certain fat-related hormones.
3. Cod liver oil might prevent negative effects of a western diet
Research published in Circulation, a journal published by the American Heart Association, studied the effect of a cod liver oil supplement in blood markers of heart disease in a small group of volunteers (3).
All volunteers consumed a “western diet,” which is known to promote heart disease. As in the study on pigs, the researchers found that blood lipid levels dropped and other biomarkers of cardiovascular well-being improved too.
4. Cod liver oil fights inflammation and lowers triglycerides
A scientific review article by Phillip C. Calder in the journal Clinical Science evaluated the range of mechanisms by which the omega 3 fatty acids in cod liver oil help reduce your risk for heart disease (4).
The omega 3 fatty acid content, according to Calder, lowers levels of blood triglycerides, helps decrease the production of inflammatory compounds in the blood, and even increases heart rate variability. All of these are positive steps when it comes to heart disease, since high triglycerides, lots of inflammation, and low heart rate variability are all associated with heart disease.
Calder also cites several epidemiological studies demonstrating the benefits of omega 3 fatty acid consumption, particularly in people who are at high risk for cardiovascular disease.
5. Cod liver oil might help prevent diabetes
One unexpected benefit of cod liver oil appears to be a potential for it to reduce your risk for type I diabetes, either when consumed during childhood.
Research published from the National Institute of Health in Norway compared mothers of children with type 1 diabetes to a matched control group of mothers of children similar in many regards, except that they did not have type 1 diabetes (5).
The results showed that mothers of children without type 1 diabetes were more likely to take cod liver oil, perhaps indicating that there may be a protective effect associated with cod liver oil.
The same authors replicated this finding in a case control study of children with type 1 diabetes (6).
Using a mail survey, the researchers again matched children with type 1 diabetes with children from similar backgrounds who did not have type 1 diabetes.
The researchers found a protective effect; using cod liver oil conferred about a 25% reduction in risk of type 1 diabetes during the first year of a child’s life.
Cod liver oil side effects
Too much cod liver oil is bad news if you are pregnant. Mothers and children should be especially conscious of the vitamin A content of any cod liver oil supplement they use, though; research in rats has found that excessive levels of vitamin A intake can cause birth defects (7).
If you don’t want to tally up your vitamin A intake so you can be sure taking a cod liver oil supplement is okay, you can also take a regular fish oil supplement, which shouldn’t have as much vitamin A in it.
The omega 3 fatty acids in cod liver oil are quite safe. Aside from a few scattered reports of very mild and transient gastrointestinal discomfort, no side effects are known to be associated with omega 3 fatty acids.
The one thing you do need to be wary of is the vitamin A content of your cod liver oil supplement. Since vitamin A is fat soluble (hence why you’d find it in an oil supplement), your body can’t get rid of excess vitamin A very easily, so high doses of vitamin A can be harmful to your health, according to the United States National Institutes of Health (8).
According to the office of dietary supplements at the National Institutes of Health, the maximum recommended intake of vitamin A is 10,000 IUs per day, which a hefty serving of cod liver oil can sometimes exceed.
Too much vitamin A can cause dizziness, nausea, and headaches. Too much vitamin A is particularly dangerous for women who are pregnant, because vitamin A overload is associated with birth defects. As such, taking cod liver oil when you are pregnant is not recommended.
Though cod liver oil is also high in vitamin D, the safety limit for vitamin D intake is far higher than vitamin A. Several thousand IUs of vitamin D taken daily over a long period of time are necessary to cause vitamin D toxicity—sources cite upper intake limits between 10,000 to 40,000 IUs per day.
With cod liver oil, you’re far more likely to run into problems because of the vitamin A content before you have any issues linked to the vitamin D content.
Cod liver oil dosage
Aim for at least 1000 mg per day. The American Heart Association currently recommends 1000 mg of fish oil per day for people with cardiovascular disease.
People with more risk factors for heart disease might want to aim for 2000-4000 mg per day. Even for those who are healthy, that’s not a bad place to start (9). However, if you already know you have high blood lipids and want to be proactive about lowering your risk for heart disease, you can consider 2000-4000 mg of fish oil per day.
Don’t overdo it with cod liver oil, because of its high vitamin A content. In the case of cod liver oil, keep in mind the caveats about vitamin A content–you don’t want to increase your intake of cod liver oil so high that you exceed your recommended daily intake of vitamin A. Don’t forget, you’ll have to take into account all of the other sources of vitamin A in your diet, too.
Cod liver oil benefits FAQ
Q: Should you take cod liver oil in the morning or at night?
A: Fish oil spends several days in your system before it is excreted, so as long as you take cod liver oil once per day, the levels of DHA and EPA in your blood will rapidly reach an equilibrium within a few days.
This equilibrium level of omega 3s won’t vary much from day to day, even if the time of day you take cod liver oil isn’t always consistent.
The vitamin D in cod liver oil might matter more when it comes to optimal timing of doses, because it essentially acts as a hormone, and we know that many hormones in the body follow a circadian rhythm.
While research has acknowledged that vitamin D is linked to sleep quality, scientists still don’t know whether it’s better to take vitamin D (and thus cod liver oil) in the morning or the evening (10).
Q: Is cod liver oil bad for you?
A: Cod liver oil is safe for most people when taken at an appropriate dose. When cod liver oil is taken at a very high dose, it can be bad for you because of the high concentration of vitamin A.
While a strong dose of vitamin A is one of the main selling points of cod liver oil, too much vitamin A can be toxic. Vitamin A is fat soluble, not water soluble, so the vitamin A in cod liver oil stays in your system for longer than water-soluble vitamins like vitamin C.
Moreover, because excessive supplemental intake of vitamin A has been linked to birth defects, cod liver oil should not’ be taken during pregnancy.
Taking more than one or two standard doses of cod liver oil can put you over the maximum recommended intake of vitamin A per day, so cod liver oil is not as well-suited for high-dose delivery of omega 3s.
Q: Is cod liver oil beneficial for hair?
A: Though cod liver oil occasionally makes appearances on lists of nutrients and supplements that can improve hair health, the scientific evidence is fairly limited to support this claim.
One study on women with hair loss does suggest a potential role for omega 3 fatty acids generally, though—the study, published in the Journal of Cosmetic Dermatology in 2015, split a group of 120 women with hair loss into two groups (11).
After taking the supplement for six months, the group taking the combined supplement showed stronger and healthier hair compared to the placebo group.
Related: Our best cod liver oil picks
Summary
Cod liver oil is a solid source of fish oil and vitamin A. It’s been studied as a way to tamp down on the risk factors for heart disease, plus improve your ability to regulate your blood sugar.
Cod liver oil is also one of the few naturally-occuring source of vitamin D, which makes it a well-rounded, nutrient-dense way to get the omega-3s in fish oil.
