People living in parts of northern Europe have been using cod liver oil for centuries to enhance immunity and protect them from dark, long winters. They have also used cod liver oil as a natural solution for rheumatism, aching joints and stiff muscles. (1)
The primary source of cod liver oil was eating the fresh livers of Gadus morhua fish. While not very appetizing to most people, traditional populations felt it was worth it to benefit from cod liver oil’s numerous health-promoting effects.
What Is Cod Liver Oil?
Cod liver oil is a nutrient-dense source of essential vitamins including vitamin D and vitamin A as well as anti-inflammatory omega-3 fatty acids. (2) Considering most people don’t eat enough anti-inflammatory foods that provide both vitamin D and omega-3s — important nutrients that play a crucial role in cardiovascular, hormonal, immune, reproductive and neurological health — many adults and children can benefit from regularly supplementing with cod liver oil.
Cod liver oil comes from, you guessed it, cod liver! You can consume the oil either from eating fresh cod liver or, more commonly, from taking over-the-counter supplements. Each teaspoon of cod liver oil has about 41 calories and 4.5 grams of fat, split between monounsaturated, saturated and polyunsaturated fatty acids. (3)
The most beneficial aspect of taking cod liver oil is that it contains high levels of omega-3 fatty acids, the same type found in oily fish or seafood like salmon, mackerel and sardines. It’s also one of the few and best vitamin D–rich foods.
1. Source of Anti-Inflammatory Omega-3 Fatty Acids
Cod liver fish oil is one of nature’s richest sources of omega-3 fatty acids, called docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Due to their natural anti-inflammatory properties, omega-3s are often used to treat a variety of symptoms naturally, from coronary heart disease risk factors to depression or arthritis pain.
There are many studied benefits of omega-3 foods or supplements, including protecting and improving heart health, battling mental disorders and decline, reducing inflammation, fighting autoimmune diseases, lowering cancer risk, supporting the growth of healthy bones and joints, improving sleep quality, benefiting child growth and development, fighting menstrual pain, lowering the risk of macular degeneration, and improving skin health as you age.
The problem is that the vast majority of Americans have an imbalance of omega-3 to omega-6 fats in their diet. Omega-6 fats aren’t necessarily bad for you, but if they are consumed in large amounts without omega-3s, they cause inflammation, which is at the root of most diseases.
A healthy ratio is ideally around 2:1 omega-6 to omega-3 fats, but many people on the Standard American Diet (SAD) consume five to 10 times more omega-6 fatty acids than omega-3s. Omega-3 deficiency is on the rise because of the overconsumption of processed foods, fast or fried foods that contain refined vegetable oils (like soybean oil, canola oil, cottonseed oil and corn oil) filled with omega-6s. Supplementing with omega-3-rich cod liver oil is one way to lower inflammation and tip your fatty acid ratio back in favor of better health.
2. Supplies Critical Vitamin D
Vitamin D acts more like a hormone in the body than a vitamin, since it affects neurotransmitter functioning, heart health and inflammatory responses. Synthesized by your own skin when you’re exposed to the sun’s UV light, the best ways to get enough vitamin D are to spend a little time outdoors without sunscreen and to eat vitamin D-rich foods.
Not only does vitamin D play a part in healthy bone metabolism, but it supports important functions of all of our cells. Because low vitamin D levels can interfere with our cells’ ability to multiply and replenish, vitamin D deficiency might increase the risk of becoming sick short-term, or, even worse, developing a chronic autoimmune disorder, cognitive or cardiovascular disease, diabetes, osteoporosis or cancer.
Many adults and children don’t get enough regular sun exposure year round due to living mostly indoor lifestyles, which is why vitamin D is a vital component of most multivitamins. One researcher reviewing the prevalence of vitamin D deficiency states in his 2008 review that “Vitamin D deficiency is now recognized as a pandemic.”(4) Low levels of vitamin D are associated with rickets in children, osteopenia, osteoporosis (and related fractures), cancer, autoimmune diseases, high blood pressure, diabetes, rheumatoid arthritis, mental illness, autism and tuberculosis. (5, 4)
High doses of vitamin D taken alone might have potential side effects, which is why it’s now recommended to take vitamin D in combination with synergistic vitamin A and omega-3 fatty acids, such as how it’s found naturally in vitamin D–rich foods including cod liver oil. (6)
3. Great Source of Vitamin A
Vitamin A is an important antioxidant that reduces oxidative stress (also called free radical damage) and, therefore, inflammation levels. It’s tied to the prevention of eye-related disorders, supports brain health, helps fight cancer and is important for hormone production. While most people eating a pretty well-balanced diet get enough vitamin A daily, deficiency is a risk for some people eating highly processed foods or not enough calories in general.
Recently, supplementing with vitamin A has come under debate, since high levels are thought to actually be harmful and potentially toxic, causing a condition known as hypervitaminosis A. However, this is generally caused by high-dose vitamin A supplements, not the amount found in a teaspoon of cod liver oil, which contains about 90 percent of your daily recommended allowance of vitamin A. (3)
When it comes to obtaining vitamin A from cod liver oil, the quality of the supplement seems to make a big impact. Many brands contain synthetic versions of vitamins A and D that aren’t well absorbed, in addition to dangerous ratios of these two nutrients. While consuming very high levels of vitamin A from supplements alone has been linked to some health concerns, obtaining vitamin A naturally from food sources can help improve the immune system. Eating plenty of vitamin A-rich foods is beneficial for bone growth, night vision, healthy cellular growth, testicular and ovarian function and much more. (7)
Vitamins A and D are fat-soluble nutrients often found together in animal foods. Both act like precursors to active hormones, so we produce certain enzymes that convert each of these to active forms the body can use to regulate our immune system. (8) In this case, vitamin A is converted to retinol. Obtaining vitamins A and D together is completely natural and allows these processes to happen in a way that protects us from toxicity.
4. Helps Prevent Heart Disease
Evidence shows that cod liver oil taken either in supplement or whole food form can help lower high triglycerides, a type of dangerous fat in the blood that raises the risk for heart disease. Cod liver oil also treats high blood pressure and helps to balance cholesterol levels. (9, 10)
A range of human and animal studies have proven high efficacy of omega-3 polyunsaturated fatty acids obtained from cod liver oil in preventing atherosclerosis (hardening and stiffening of the arteries) and its complications. Treatment either alone or in combination with statin drugs helps reverse risk factors in patients with hypertriglyceridemia and high triglyceride levels. (11)
5. Lowers Risk for Cancer
High levels of vitamin D, obtained from both sun exposure and supplementing with cod liver oil, have been associated with lower risks of cancer. One study found that vitamin D from both the sun and cod liver oil could help prevent breast cancer in women due to having antiproliferative and proapoptotic effects on breast cancer cells, thereby reducing mammary tumors. (12)
While sun exposure still seems to be the most relevant protective factor for getting enough cancer-busting vitamin D, cod liver oil may also help offset common deficiencies.
6. Prevents or Treats Diabetes
As a great source of essential healthy fats, cod liver oil can help control insulin resistance, inflammation and manage glucose (sugar) levels in the blood. It’s even been shown to help lower symptoms of complications related to diabetes like kidney disease. Use of cod liver oil and vitamin D supplements during the first year of a baby’s life and use of cod liver during pregnancy can also help lower the risk for developing diabetes. (13)
One 2007 study published in the Journal of Pharmacy and Pharmacology found that giving diabetic rats cod liver oil supplements for 12 weeks acted as a natural diabetes treatment. The cod liver oil supplements completely prevented endothelial deficiency and helped correct several biochemical markers for metabolic syndrome (a combination of diabetes and cardiovascular disorder risk factors). (14)
Prior to supplementing with cod liver oil, the rats experienced elevated plasma glucose (sugar) levels and high triacylglycerol and high cholesterol concentrations in their blood. Cod liver oil helped manage the rats’ weight gain and entirely prevented plasma lipid abnormalities while also controlling insulin sensitivity and other factors.
7. Helps Treat Rickets and Rheumatoid Arthritis
At the beginning of the 20th century, scientists established that cod liver oil was a natural “antirachitic,” which meant thousands of mothers began forcefully spoon-feeding the stuff to unwilling children to avoid painful rickets. Cod liver oil use is associated with a reduction in pain, joint stiffness and swelling in patients with arthritis and other inflammatory conditions. (11)
8. Boosts Reproductive Health and Infant Development
Omega-3 fatty acids are important for reproductive health and ideal for a pregnancy diet. These fats found in cod liver oil and other aquatic sources are “precursors” to eicosanoids, compounds that affect cellular activity. Eicosanoids are involved in the inflammatory process and help to keep that in check, but they’re also associated with menstrual cycles, fertility and many hormone-related functions.
When you don’t have enough omega-3s in your diet, the functions fulfilled by eicosanoids can be disrupted, which is why increasing omega-3 intake may improve issues with the following hormone and reproduction-related conditions: (16, 17, 18, 19)
- dysmenorrhea (menstrual cramps)
- inconsistent ovulation
- premature birth
- low birth weights
- infant brain development during pregnancy and breast-feeding
- postpartum depression
- postmenopausal osteoporosis
- breast cancer
- low sperm count
- poor sperm motility
Results from a 2003 study conducted at the University of Oslo in Norway showed that children who were born to mothers who had taken cod liver oil during pregnancy and lactation scored higher on intelligence tests at age four compared with children whose mothers had taken corn oil instead. (20)
9. Improves Brain Function
Regularly supplementing with fish oil as a natural remedy for depression has been associated with lower risks for depressive symptoms, due to both the higher intake of essential omega-3 fats and vitamin D. (21)
A 2007 study published in the Journal of Affective Disorders found that omega-3 fatty acids from cod liver oil improved the outcome of depression and anxiety in the general population. The Hordaland Health Study followed 21,835 adults living in Norway for two years and discovered that the prevalence of depressive symptoms in those who used cod liver oil daily was 2.5 percent, as compared to 3.8 percent in the rest of the population. They also found that the prevalence of high levels of depressive symptoms decreased with increasing duration (0–12 months) of cod liver oil use. (22)
There’s a strong connection between omega-3 intake or fish oil supplementation and prevention of cognitive decline, including Alzheimer’s disease. While no long-term human trials have successfully used fish oil to offset the development, there is tentative evidence that omega-3s it contains (as well as nutrients like vitamin B types, vitamins E, C and D) may serve to protect against cognitive decline and potentially decrease a person’s chance of developing this debilitating condition. (23, 24, 25)
10. Helps Maintain Bone Health
Vitamin D is important for building and maintaining strong bones. Studies show that women who live in cold, northerly latitudes and don’t get enough sunlight tend to produce less vitamin D, which increases the risk for bone turnover, bone loss, fractures and also obesity. (26)
11. Fights Ulcers
In laboratory settings, cod liver oil has shown benefits for improving gastric ulcer healing and reducing gastric antisecretory effects observed in rats. The oil also seems to produce gastric cytoprotective effects and causes a significant reduction in the development of stress and pain caused by gastric ulcers. (28)
Many fish oil supplements available today are unhealthy, contain fillers or synthetic ingredients, can be rancid and are not an ideal ratio of fatty acids. Look for a reputable brand and ideally one that also contains antioxidants like astaxanthin to keep the oil from oxidizing.
Fermented cod liver oil is also available by some brands, which means the livers were fermented to produce more vitamins and is predigested. Fermentation is a valuable process that makes nutrients much more bioavailable.
Since it’s not associated with any significant side effects, cod liver oil can be taken by most people in a varying number of dosages. For the average person, it’s best to get about 500 milligrams of EPA/DHA per day (at least two servings of a 3.5-ounce serving of oily fish), while up to 4,000 milligrams EPA/DHA is recommended in some cases, particularly if you’re aiming to treat or prevent heart disease. (29) Figure out what works best for you, and focus more on the milligrams of EPA/DHA than an exact amount of fish oil.
How should you consume your fish oil? You can mix it with a small amount of juice, lemon water, a smoothie, apple sauce, yogurt, almond butter or anything else that helps disguise the slightly fishy taste. A reputable brand will not add flavor enhancers or remove the odor or taste, so be prepared! Some brands will add natural extract to improve the taste (like mint or lemon), so this is an option.
Store your bottle of cod liver oil in a cool, dark place or in the refrigerator to keep it from spoiling and going rancid.
Risks and Side Effects
When it comes to cod liver oil, and any type of fish oil or omega-3 supplement for that matter, it all comes down to the need for balance. Remember, you’re aiming to get about two times the amount of omega-3s to omega-6s in your diet, while the average American may get 5–10 times more omega-6s than omega-3s on a regular basis.
Omega-3 fatty acids suppress inflammation and omega-6 fatty acids promote inflammation, and we need some of both. This delicate relationship keeps your immune system working properly so you produce “defense mechanisms” against posed threats (toxins, bacteria, pathogens) when you need to, but don’t become overly inflamed in the process.
In general, the best way to achieve balance is by getting your omega-3s from food sources like wild-caught fish (such as salmon), grass-fed or pasture-raised meat or cage-free eggs. Nuts and seeds are also good choices but supply a different, plant-based kind of omega-3 known as ALA, while animal sources provide the preferred types called EPA and DHA. Only about one percent of ALA converts to EPA, which your body can actually use, so if you’re following a vegan diet or similar, it’s important to get as much ALA as possible.
If you’re consuming wild-caught fish a couple of times a week and have a diet high in pastured animal fats and plant-based omega-3 foods, then taking an omega-3 supplement might not be totally necessary. However, the average person can really benefit from supplementing and eating well.
Cod liver oil can act like a blood thinner, so pregnant women, asthmatics or people taking high blood pressure medication or anticoagulants should speak to their doctor before beginning a fish oil regimen. While it’s safe for most people, there are some possible side effects, such as belching (having “fish burps”), bad breath, heartburn, nausea, blood stools, low blood pressure, high vitamin A and D levels and nosebleeds. (30)
The major benefits of cod liver oil include:
- Source of anti-inflammatory omega-3 fatty acids
- Supplies critical vitamin D
- Great source of vitamin A
- Helps prevent heart disease
- Lowers risk for cancer
- Prevents or treats diabetes
- Helps treat rickets and rheumatoid arthritis
- Boosts reproductive health and infant development
- Improves brain function
- Helps maintain bone health
- Fights ulcers
There are no known major side effects to taking a cod liver oil supplement, so the dosage you choose will mostly depend on what you’re aiming to accomplish. Typical doses of EPA/DHA each day range between 500 and 4,000 milligrams.
To use cod liver oil, it’s best to mix it into something that will temper the strong flavor it has, like a smoothie.
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