Cod liver oil (Gadus morhua [Linnaeus, 1758]) is a revered 8th century natural medicine that strengthens the body, relieves joint pain and treats skin problems. Cod liver oil’s reputation continued into the 21st century, and is experiencing a resurgence of interest within the scientific community (R. D. Semba, 2012). Several reasons for this renewal may be linked to cod liver oil’s unique constituent profile which affords meaningful levels of naturally occurring vitamins A (retinol), D3 (cholecalciferol), and the family of essential long-chain omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Cod liver oil’s composition can prevent multiple micronutrient deficiencies consistent with the United Nations Millennium Development Goals 2015 and Beyond. Additionally, consuming cod liver oil offers a safe and cost-effective way to ingest the nutritional benefits of seafood necessary to meet physical requirements for optimal health. Increasing the dietary status of vitamin D alone in Western Europe has been estimated to alleviate the economic burden of disease by $293 billion per year (Bengtson Nash, Schlabach, & Nichols, 2014). We find ourselves going back to the future to revisit the health benefits of this remarkable fish oil driven by economic and food resource pressures.
This paper delves into the story behind cod liver oil’s resurgence. It explores 1) cod liver oil’s impressive empirical record for treating a wide variety of complaints from skeletal problems to infections; 2) the scientific community’s exploration of potential synergistic relationships between cod liver oil’s key constituents; 3) new methods of minimally processing cod liver oil that preserve its “virgin” crude constituent profile while removing environmental contaminants; and, 4) an overview of cod liver oil’s contemporary clinical applications.
Cod Liver Oil – 8th through 21st Centuries
Marine liver oils have enjoyed a reputation as a health promoting food and therapeutic intervention for millennia by maritime cultures around the world. In 5th century BC Mediterranean culture, the Greek physician, Hippocrates, mentions using dolphin liver oil internally and topically for chronic skin eruptions. Earlier than the 8th century, ancestral fishing communities living on the shores of the Atlantic Ocean, North, Baltic and Norwegian Seas, are known to have used Atlantic cod liver oil (Gadus morhua [Linnaeus, 1758]) therapeutically in poultices, salves, and ointments as well as, internally, as a strengthening tonic and remedy for joint complaints. Norwegian fisherman rubbed cod liver oil on their joints and muscles to ease soreness (Brockbank, 1904; Guy, 1923; Haywood, 2000; MarineBio Conservation Society).
In 1650, rickets, the softening and weakening of bones in children leading to lifelong bone deformity, was acknowledged as a disease by an esteemed Cambridge physician, Frances Glisson. This condition was so pervasive and crippling in 17th century British Isles that it was called “the English Disease.” The application of cod liver oil for rickets, was a welcome and gentle option to prevailing treatments that were painful, ineffective and incapacitating (DeLuca, 2014; Rajakumar, 2003; Rosenfeld, 1997).
In Glisson’s own words, he “…suggested treatments for rickets included: cautery, incisions to draw out bad humors, blistering, and ligature of soft wool around the limb to retard the return of blood. For correction of bony deformities, Glisson proposed splinting and artificial suspension of the affected infant: ‘The artificial suspension of the body is performed by the help of an instrument cunningly made with swathing bands, first crossing the brest and coming under the armpits, then about the head and under the chin, then receiving the hands by two handles, so that it is a pleasure to see the child hanging pendulous in the air, and moved to and fro by the spectators. This kind of exercise is thought to be many waies conducible in this affect, for it helpeth to restore the crooked bones, to erect the bended joynts, and to lengthen the short stature of the body’ (Rajakumar, 2003).
The early 18th century witnessed Northern European infirmaries and apothecaries prescribing cod liver oil to patients suffering from rickets and rheumatism based on the oil’s observed success as a folk remedy. By 1770, cod liver oil was adopted into conventional practice as a therapeutic agent by British and Northern European physicians solely on clinical empiricism and without any satisfactory explanation accounting for its superiority. The English doctor Samuel Kay of the Manchester Infirmary was credited with being the first to introduce the internal medical use of cod liver oil. Dr. Thomas Percival and Robert Darbey, from the Manchester infirmary, chronicled its spectacular effects in the treatment of chronic rheumatism, and Percival reported their results to the Medical Society on October 7, 1782(Abler).
Cod liver oil’s healing properties were recognized as more than skeletal. ‘‘Whether the disease of rickets be in its most severe form, with swollen joints and crooked legs, or at its commencement, the cod liver oil will supersede every other means of cure’’ and ‘‘a case of inflammation of the eyelids and intolerance of light was cured within ten days with cod liver oil as were several cases of conjunctivitis of the cornea’’ (Carpenter, 1998).
The relationship between rickets and increased susceptibility to colds, bronchitis, and pneumonia was a frequent observation. In 1845, Dr. Graham Bradshaw speaking to the British Royal Society of Physicians and Surgeons described the remarkable clinical effects he had witnessed in his patients that were administered cod liver oil. He broadened its use to include patients suffering from various forms of arthritis as well as improvement in patients with tuberculosis (Bradshaw, 1845). He later reported a series of case histories of these successes in papers that were published in the Provincial Medical and Surgical Journal. He indicated that he had learned of the value of cod liver oil from a Belgian colleague, Dr. A Burgraeve who had spent time in Norway and witnessed the medicinal effectiveness of cod liver oil (Bills, Massengale, HICKMAN, & GBAY, 1938; Toogood, 1846).
By the end of the 19th century, based on the durability of accumulating evidence, cod liver oil was generally accepted to include treatment for rickets and osteomalacia, generalized malnourishment, certain eye and skin conditions and infections (Rosenfeld, 1997) despite the scientific dogma that fats – whether from lard, butter, or cod-liver oil – were considered interchangeable in nutrition (R. Semba & Kramer, 2012).
Over the next 100 years ago, it became well recognized that cod liver oil was different from other types of marine, animal or vegetable oils in its healing properties. The evolving story of its profound versatile nature and increasing acceptance in medicine began with the emergence of the concept of “dietary deficiency diseases” in concert with the discovery and isolation of vitamins, specifically, vitamins A (retinol) and D3 (cholecalciferol), beginning in the early 20th century(DeLuca, 2014).
Clinical observation of vitamin deficiencies preceded their isolation, structural descriptions and synthesis. The appreciation of vitamin A’s contribution to cod liver oil’s effects on immunity, earning it the name the “anti-infective” vitamin, came before the recognition of vitamin D’s influence on bone development(R. Semba & Kramer, 2012; R. D. Semba, 1999). Largely through the influence of Sir Mellanby, in the UK. vitamin A, given as cod liver oil, underwent a period of intense clinical investigation. Between 1920 and 1940, at least 30 trials were conducted to determine whether vitamin A could reduce the morbidity and mortality from infectious diseases, including respiratory disease, measles, puerperal sepsis, and tuberculosis. By the 1930s, it was established that vitamin A supplementation could reduce morbidity and mortality in young children. Supplementation reduced the mortality of vitamin A-deficient children with measles by nearly 60%. Vitamin A, given as cod liver oil, became a mainstream preventive measure; cod liver oil was part of the morning routine for millions of children and was acknowledged in saving the lives of children from poor families in England (R. D. Semba, 2012).
The unraveling of vitamin A and D in cod liver oil appears as an informal collaboration between Sir Mellanby in the UK and McCollum and colleagues in the United States. Concerned with the prevalence of rickets and intrigued by the work of McCollum eon vitamin A, Mellanby decided that rickets might be a dietary deficiency disease, a controversial concept at that time. In 1919, he used the diet consumed by the Scottish people (who had the highest incidence of rickets), primarily oatmeal, and fed that diet to dogs that he inadvertently kept indoors and away from sunlight. The dogs developed rickets, which was identical to the human disease. Mellanby could cure the dog’s disease by providing cod liver oil, a standard of care at that time (Mellanby, 1988). He assumed that it was possible that recently discovered vitamin A in cod liver oil was responsible for the prevention of rickets (DeLuca, 2014; R. Semba & Kramer, 2012).
McCollum had been following Sir Mellanby’s finding and decided to test the hypothesis of whether vitamin A was responsible for healing rickets. He bubbled oxygen through cod liver oil that destroyed vitamin A and found that this preparation was no longer able to prevent xerophthalmia (dry eyes), skin problems, weakened immune function and other symptoms of vitamin A deficiency, but it still retained the ability to cure rickets. McCollum and colleagues correctly concluded that the factor that cures rickets is a new vitamin, which they called vitamin D (DeLuca, 2014). The European medical community adopted the use of cod liver oil earlier than the United States. Perhaps this is because of Europe’s proximity to Scandinavia, exposure to Norse folklore and the availability of cod liver oil.
In the United States, from the 1920s through the 1950s, the British regimen of daily cod liver oil use was adopted by physicians and endorsed by the US Government. Supplementation began when infants were only a few months old. Cod liver oil was used for tuberculosis and other ‘‘wasting’’ diseases (Linday, 2010).
While rickets was rampant among poor children living in the industrialized and polluted northern cities in the United States, the value of cod liver oil was largely dismissed as a folk medicine. By the 1930s, only after the discovery of vitamin D, and the delineation of the anti-rachitic properties of cod liver oil, did it become possible to not only treat but also eradicate rickets in the United States. Cod liver oil became an indispensable part of every child’s diet (Rajakumar, 2003).
Cod-liver oil represented a whole food source of two “new” essential nutrients with demonstrated significant healing benefits: vitamin A for growth, healthy eyes and immune function and vitamin D for proper bone development (R. D. Semba, 2012).
The unfolding of cod liver oil’s unique active principles does not end with vitamins A and D. In the late 20th century, it continues with the identification of a class of fats known as essential long-chain omega-3 polyunsaturated fatty acids (ω3FA) found in cod liver oil. In 1978, J Dyerberg and Bang (1978) reported that the incidence of myocardial infarction was very low in Greenland Eskimos whose diet consisted of marine lipids rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (J Dyerberg & Bang, 1978; Spector & Kim, 2015).
The age of chemistry ushered in the ability to partition foods, isolate and synthesize their discrete molecules. The emerging fields of biotechnology, molecular biochemistry and nutrigenomics are rapidly advancing our understanding of how food and its derivatives interact with our genome to make marked changes in gene expression for better or worse (Subbiah, 2008). This “omics” revolution explores how food-specific molecules influence cellular communication which can substantially affect our quality of life and longevity. On the other hand, this new research directive supports food fortification and reinforces the use of isolated nutrients and engineered supplements over whole food extracts and concentrates.
In the case of cod liver oil, vitamins A, D and ω3FA taken alone or in combination have become the preferred bio-actives over consuming cod liver oil, the parent that supplies all three. While there is a large body of evidence on the benefits of the individual nutrients (Table 1), cod liver oil’s place in the dietary supplement and therapeutic decision tree warrants clarification owing to its remarkable history for the treatment for inflammation, immune and bone disorders.