A standard supplement in European and American households for centuries, cod liver oil has been used to treat a variety of health issues, many of which have been studied and verified through clinical research. However, it wasn’t until around the turn of the 21st century that scientists began to discover cod liver oil’s potential benefits in lowering cholesterol levels.
Cod liver oil is made from the livers of Gadus morhua and other species of cod. Although some cultures eat fresh cod liver, most people take it in the form of supplements, either in bottled oil that is sometimes flavored, or via cod liver oil capsules.
During the early part of the 20th century, cod liver oil was discovered to be a cure for rickets and was also often used for arthritis and stiff muscles, according to the “Medscape Journal.” It may also have benefits in treating high blood pressure and kidney disease in patients with type 2 diabetes.
The National Institutes of Health reports that current scientific thinking is that fish oils may lower your cholesterol by keeping it from being absorbed in the intestine, with further evidence that using vitamin B12 along with fish oils might increase their ability to lower cholesterol levels. According to the “Medscape Journal,” fish oil’s protective benefits in reducing blood-fat lipid triglycerides and increasing HDL, or "good cholesterol," is also due to the effects of omega-3 fatty acids in the oil.
There is some evidence suggesting that birth control pills may interfere with the triglyceride-lowering benefits of fish oils, so if you are taking contraceptives and also have high blood lipid levels including both triglycerides and cholesterol, you should check with your doctor about using fish oil supplements. For all other people, the National Institutes of Health website MedlinePlus recommends taking 1 to 4 g daily of fish oils to treat high cholesterol and triglycerides.
A study led by H. Shimokawa and P.M. Vanhoutte and published in 1988 in the American Heart Association’s journal “Circulation” investigated the effects of cod liver oil supplements on high cholesterol and hardened arteries in pigs and found that the cod liver oil demonstrated protective benefits by delaying degeneration of the endothelium layer of cells in blood vessels and helping to relax the smooth heart muscles. A study from the University of Tromsø, Norway, and published in 1993 in the “European Journal of Clinical Nutrition” showed that cod liver oil lowered triglycerides in men and LDL, or "bad cholesterol," levels in woman, although the LDL levels in men were raised slightly. Researchers at the Steno Memorial Hospital in Gentofte, Denmark, in a 1989 study published in the “New England Journal of Medicine” looked at insulin-dependent diabetics and discovered that dietary supplementation with cod liver oil resulted in improving the levels of the good cholesterol and in decreasing levels of the bad very-low-density lipoprotein cholesterol and triglycerides.
Some people who are allergic to seafood may also be allergic to fish oil supplements. Fish oils have also been known to reduce vitamin E levels in your blood. According to RXList.com, cod liver oil is generally well-tolerated but may cause side effects such as belching, bad breath, heartburn, nausea, diarrhea and nosebleeds, especially with high doses. The “Medscape Journal” also recommends that you avoid cod liver oil if you are pregnant, asthmatic or on a blood thinner such as warfarin.