From better vision to better mood, you'll find that the benefits of cod liver oil are extensive and promising. While it's been used as a remedy for generations, researchers are now just diving into what makes cod liver oil so good for you - and why you should pay a little more attention to this old-fashioned supplement.
What is cod liver oil?
Cod liver oil is a fatty substance extracted from the livers of codfish, and people use it as a dietary supplement because it is rich in essential fatty acids and key nutrients such as vitamins A and D.
Northern Europeans, particularly in Scandinavia and the Hebrides, have used cod livers as food and cod liver oil for its health benefits for generations. It was thought to fortify the body against cold, dark winters(1). Given that winters at extreme northern latitudes tend to be long with little sunlight, cod liver oil would offer an excellent source of vitamin D when consistent exposure to sunlight itself wasn't possible.
The earliest recorded use of cod liver oil as a therapeutic supplement dates to 17th century England when writers described its use in fighting rheumatoid arthritis as well as joint pain and inflammation (2). The use of cod liver oil as a remedy continued throughout the 19th century into the early 20th century when it was used to treat consumption (a lung disease) and rickets, a disease caused by vitamin D deficiency (3). By the 1930s, it became a common daily supplement for many European and North American children.
Cod liver oil is a good source of three specific nutrients: omega-3 fatty acids, vitamin A and vitamin D (4). It's these healthy fats and fat-soluble vitamins that are likely responsible for so many of cod liver oil's benefits. While you can get these nutrients from a variety of other foods, such as cold-water fish and organ meats, cod liver oil is the single densest source of these key nutrients.
A teaspoon of cod liver oil contains about 40 calories, 4500 IU vitamin A, and 450 IU vitamin D as well as 888 mg omega-3 fatty acids. This represents about 90% of the daily value for vitamin A and 113% of the daily value for vitamin D.
- Docosahexaenoic acid (DHA) is an omega-3 fatty acid and an essential nutrient, especially for the brain (5), vision, and nervous system (6). DHA's protective role on neurological health and brain development makes it a particularly important fat for babies and young children whose brains and bodies are growing quickly.
- Eicosapentaenoic acid (EPA) is an omega-3 fatty acid that acts as a partner to DHA, and you'll often see them referenced together. Eicosapentaenoic acid supports the heart (7) and is a key nutrient for combatting inflammation and supporting mood (8).
- Vitamin A is a fat-soluble vitamin that performs several important functions for your body. Among its most important roles are supporting your vision and immune system function as well as cellular and reproductive health (9). It is also a powerful antioxidant.
- Vitamin D is also a fat-soluble vitamin, and it plays a critical role in bone health, and deficiency in the vitamin is linked not only to bone diseases such as rickets, but also to depression (10, 11) as well as poor heart and metabolic health, autoimmune disease, and even cancer (12).
Benefits of Cod Liver Oil
You can attribute most of the benefits of cod liver oil to its omega-3 fatty acids and high vitamin A and D content. We know that, individually, these nutrients help support the heart, bones, and eyes as well as cognitive, reproductive, and immune system health. And it's fair to extrapolate some of these benefits to foods that are rich sources of these key nutrients, especially when they're used in the context of an otherwise nutrient-dense diet.
Chronic inflammation and oxidative stress are at the root of many diseases and health problems. The key nutrients in cod liver oil are highly anti-inflammatory. Low levels of vitamin D are associated with many inflammatory diseases (13). Increasing vitamin D intake through food, supplements, or sunlight exposure may help achieve optimal benefits (14).
In addition to vitamin D, vitamin A is also a powerful antioxidant that fights inflammation. And cod liver oil is an excellent source of it, containing roughly 4500 IU or about 90% of the daily value in a single teaspoon. The vitamin A in cod liver oil is retinol (or true, preformed vitamin A).
The anti-inflammatory benefits of cod liver oil, specifically, have been studied, too. One study took a look at the inflammatory marker c-reactive protein in athlete's blood. The researchers found that people who took cod liver oil regularly had lower levels of inflammation (15).
Vitamin D is a nutrient that is critical for healthy bones. Cod liver oil is the single richest food source of this nutrient, containing about 450 IU of vitamin D per teaspoon.
Maintaining good vitamin D levels helps to support bone mineral density, and taking cod liver oil is appears to be a good way to just that (16, 17). This is especially true for people who live far away from the equator, and who do not have enough access to sunlight to produce adequate vitamin D year-round (18).
One of the key nutritional benefits of cod liver oil is that it is rich in docosahexaenoic acid (DHA), an omega-3 fatty acid that plays a large role in human health - especially cognitive health. It plays a critical role in cognitive health throughout your lifetime, including in infancy and childhood as well as old age (19). A high intake of DHA along with other key nutrients, such as vitamin D, may help support brain function and cognitive ability (20).
This is especially important for pregnant women and breastfeeding mothers. Maternal intake of DHA during pregnancy and while breastfeeding conveys benefits to their babies (21). A study in Norway found that the babies of women who had higher intakes of DHA during pregnancy exhibited better problem-solving skills, which is associated with higher IQ (22).
Together, vitamins A and D as well as omega-3 fatty acids appear to support heart health. Cod liver oil is a rich source of all three nutrients. While research on the way cod liver oil benefits the heart directly is limited, examining the role of these nutrients can help give us a picture of how they work together.
Vitamin A is a powerful antioxidant and it helps calm inflammation, and some researchers have examined the nutrient's role in inhibiting the development of heart disease (23). Vitamin A can help neutralize free radicals that contribute to poor heart health (24).
People who regularly eat fish tend to have better cardiovascular health than those who don't, and researchers attribute this benefit to fish's high omega-3 fatty acid content (25, 26). Cod liver oil is a concentrated source of these healthy fats.
The nutrients found in cod liver oil benefit mood, too. Omega-3 fatty acids, as well as vitamin D, play a role in mood. People with lower levels of EPA and DHA, omega-3 fatty acids found in cod liver oil, tend to experience higher rates of severe anxiety and depression (27). And omega-3 fatty acids have a neuroprotective effect which may explain why they appear to ease anxiety and depression in some people (28). Adolescents with lower levels of vitamin D tend to experience depression and disturbed mood at higher rates than those with adequate levels, and vitamin D supplementation appears to offer some alleviation (29).
The vitamin A and omega-3 fatty acids in cod liver oil appear to benefit vision and eye health, too. This is especially true for glaucoma and age-related macular degeneration.
Glaucoma is the second leading cause of blindness in the world, and research suggests that both omega-3 fatty acids and vitamin A can play a protective role in eye health. Given that cod liver oil combines both nutrients in a single supplement, researchers are hopeful that it may offer vision support for those who need it most (30). Similarly, people with higher intakes of omega-3 fatty acids tend to have a lower risk of macular degeneration (31).
Why Take It?
While the benefits of cod liver oil are fairly clear, more research into its specific effects and its use as a supplement is always needed. It's important to note that it's a concentrated source of these key vitamins, and many of the diseases mentioned above are associated with a low intake of these key nutrients.
Currently, vitamin D deficiency is rampant in the U.S. with 70% (32) of US children and 42% of adults (33) having insufficient or deficient levels of the vitamin. Further, 95% of children and 68% had lower than optimal levels of omega-3 fatty acids. For 88% of adults, that put them in the high-risk category for heart disease (34).
Given the strikingly inadequate levels of both vitamin D and omega-3 fatty acids coupled with their relative benefits to health and well-being, finding a way to increase their intake is important. Cod liver is a rich source of both nutrients, and easy to take.
It's important to note that you can get omega-3 fatty acids from plant sources, but marine sources, such as cod liver oil and cold-water fish, are optimal. For example, flax seeds are rich source of alpha-lipoic acid (ALA), but the human body has a difficult time making the conversion from ALA to the more valuable EPA and DHA which is why eating fish (or taking a marine oil supplement like cod liver oil) is important (35, 36).
What's the alternative?
If you can't take cod liver oil, you can get many of its benefits by eating foods rich in omega-3s, vitamin A, and vitamin D. Spending an appropriate amount of time in the sunlight to optimize vitamin D levels is also helpful, too.
For EPA and DHA, eat plenty of sustainable seafood such as wild-caught salmon, rockfish, anchovies, and sardines. Caviar and fish roe are also en excellent source, too. Some people who avoid fish will take an algal oil supplement instead.
For vitamin A, eat organ meat such as liver in pâté or take dessicated liver suplements. These are source of retinol or true vitamin a, the same kind that gives cod liver oil its benefits.
You can also eat plenty of vividly colored fruits and vegetables such as leafy greens, carrots, mangos, and papaya. These contain beta carotene which, in the right circumstances, your body can convert to true vitamin A.
For vitamin D, try eating plenty of oily fish such as salmon, mackerel, herring and halibut as well as oysters. Liver is also a fairly good source of the vitamin, too.
How much cod liver oil should you take?
The typical dose for cod liver oil is 1 teaspoon daily for adults and a few drops up to ¼ teaspoon daily for children. For my family, I take 1 teaspoon cod liver oil daily during the winter months when I have less access to the sunlight, and less during the summer.
Remember to talk with your health care provider before starting any new supplements, including cod liver oil, and do not take more than the manufacturer's recommended dose without talking with your doctor first.
Risks and Side Effects
Many women who are pregnant or breastfeeding take cod liver oil because of its high DHA and vitamin D content, since these nutrients support their growing baby. Some research suggests it supports metabolic health and blood sugar regulation during pregnancy while also fighting inflammation (37).
However, other experts warn that the high vitamin A content of the supplement may pose a risk to the developing baby. As always, check with your doctor or midwife to determine what's right for you, your baby, and your pregnancy.
Additionally, cod liver oil is rich in omega-3 fatty acids. As a result, it may interact with certain medications, especially blood thinners (38). You should always talk to your doctor before beginning new supplements, especially if you take medication.
What to look for when buying a cod liver oil
Cod liver oil is typically produced from the livers of Atlantic cod, which has been historically plagued with sustainability issues such as overfishing, although stocks are improving especially in well-managed fisheries (39). Buy oil from producers who practice sustainable fishing techniques, such as catching by hook-and-line, or who are certified sustainable by the Marine Stewardship Council.
In addition, cod liver oil is fragile thanks to its omega-3 fatty acid content. In essence, without proper care it'll go rancid quickly and you'll lose all of the cod liver oil's benefits. So look for oil that is carefully handled from production, through bottling, to storage. It should have a pale, straw color and a fresh, slightly fishy flavor.
Look for brands that produce a clean, fresh-tasting oil and that use sustainable methods from well-managed fisheries. In addition, a good-quality brand of cod liver oil will typically have certificates of analysis and make those available to the public upon request.
Rosita Extra Virgin Cod Liver Oil is premium cod liver oil with impeccable sourcing. It's sustainably produced from Arctic cod caught one fish at a time by hook-and-line. They post the results of their testing publicly on their website, too.
Dropi Cod Liver Oil also produces an excellent oil from sustainably managed Icleandic fisheries. They also offer the ability to trace each bottle one their website for increased transparency.
Nordic Naturals Arctic Cod Liver Oil makes cod liver oil that is available both as liquid form and in capsules. It's sustainably sourced in Norway and easy to find in most well-stocked health food stores as well as online.
While both fish oil supplements and cod liver oil are good sources of omega-3 fatty acids including docosahexaenoic acid and eicosapentaenoic acid, only cod liver oil contains vitamins A and D. These vitamins are absent in regular fish oil.
You can find cod liver oil in any well-stocked natural foods store; however, oil quality varies from brand to brand. So you may wish to buy higher quality oils from brands practicing ethical and sustainable fishing techniques, and these brands are easily available online directly from their manufacturers or from stores specializing in natural foods and supplements.
Store unopened bottles in a cool, dark cupboard and pay attention to the use-by date on the bottle. Keep opened bottles in the fridge for up to 3 months, taking care to seal the bottle tightly each time you open it.
Cod liver oil capsules are resistant to oxidation and can be stored at room temperature, away from light and heat until the expiration date on the bottle.
Cod liver oil should taste pleasant and clean, similar to fresh sushi. If it has an acrid or rancid aroma or flavor, discard it.
You can take cod liver oil by spoon or in capsule form. In the early 20th century, when cod liver oil was commonly given to small children, mothers would often serve it with orange juice to off-set the oil's flavor.
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