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Cod Liver Oil

The role of vitamin D in Cod Liver Oil

Cod liver oil is a traditional source of vitamin D in Iceland as it is in other Nordic countries. A follow-up study of 50–70 year old women from the Norwegian Nord-Trøndelag Health Study found that older women who had taken cod liver oil as children had significantly lower forearm bone mineral density (BMD) in their old age compared to those who had not [1].

Vitamin D plays an essential role in regulating calcium and phosphate metabolism and maintaining a healthy mineralized skeleton. Humans obtain vitamin D from sunlight exposure, dietary foods and supplements. There are two forms of vitamin D: vitamin D3 and vitamin D2. Oily fish and cod liver oil are natural sources of vitamin D3, which is also produced by the skin. Vitamin D2 is synthesized from ergosterol and found in yeast and mushrooms. When vitamin D reaches the bloodstream, it is first transformed into 25-hydroxyvitamin D [25(OH)D] by 25-hydroxylase in the liver. Then, it is further processed into 1,25-dihydroxyvitamin D [1,25(OH)2D] by 25-hydroxyvitamin D-1α-hydroxylase in the kidneys. For 1,25(OH)2D to carry out its physiological actions, it must bind to its nuclear vitamin D receptor. These functions include: promotion of intestinal calcium and phosphate absorption, renal tubular calcium reabsorption, and calcium mobilization from bone [2].

Long-term insufficiency or deficit in vitamin D increases the risk of osteoporosis. Intestinal calcium absorption decreases when serum 25(OH)D levels are below 30 ng/mL. This results in a drop in serum ionized calcium and secondary hyperparathyroidism as a compensatory mechanism [2].

The expression of vitamin D receptors is shown in skeletal muscle, which may need vitamin D to function at its best. A lack of vitamin D affects proximal muscle performance and may increase the risk of falls in older adults. Research indicates that there was an improvement in proximal muscular strength and performance speed when 25(OH)D levels grew from 4 to 16 ng/mL. These improvements persisted even when levels reached over 40 ng/mL. While the results of a trial that administered 400 IU of vitamin D3/day did not demonstrate the usefulness of vitamin D3 in preventing falls, another study found that giving 800 IU of vitamin D3/day along with calcium considerably reduced the risk of falling. This data suggests that taking calcium and vitamin D supplements in amounts of at least 800 IU per day can reduce the incidence of falls, but lower doses of the vitamin did not show the same protective effects [2].

 

Reducing Elevated Lipid Parameters

The health benefits of cod oil have been of considerable interest to medicine due to its promising results. Some studies have shown a positive association, while others did not. A high dietary intake of omega-3 fatty acids has been demonstrated to have beneficial therapeutic effects by lowering the synthesis of very-low-density lipoproteins (VLDL), with subsequent low levels of blood triglycerides (TG). These findings are supported by several experimental and longitudinal investigations. Consuming fish has also been linked to a negative correlation with serum total cholesterol (TC). Due to its alteration with body lipid contents, the possible beneficial influence of polyunsaturated fatty acids found in dietary fish oil can be of value in preventing atherosclerosis, ischemic heart disease, hypertension, and diabetes mellitus (DM) [3].

Preventing Myocardial Infarction

Myocardial infarction (MI) is defined as irreversible damage due to myocardial necrosis in the setting of myocardial ischemia. The presence of recently developed ischemia symptoms, abnormalities in the electrocardiogram (ECG), an increase in cardiac biomarkers, and imaging evidence of a recent loss of viable myocardium in the form of a regional wall motion abnormality all contribute to the diagnosis. Incorporating cod liver oil into the diets of individuals who are prone to heart disease has demonstrated a range of positive effects, from a modest reduction in hypertension to a drop in the synthesis of low-density lipoprotein, which in turn lowers the risk of MI [4].

Omega-3 fatty acids have for long been shown to reduce the incidence of cardiovascular (CV) diseases. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the two primary forms of omega-3 fatty acids found in fish oil. Cod liver oil is found to have a high concentration of these omega-3 fatty acids. It has been suggested that dietary EPA protects the myocardium by lowering local inflammation and lowers the risk of arterial thrombosis. A study on hyperlipidemic pigs showed that supplementing with cod liver oil prevented the development of atherosclerosis in these animals [4].

The cardiometabolic effects of omega-3 fatty acids is an active area of research. It reduces the content of arachidonic acid (AA) in membrane phospholipids in platelets, endothelial cells, and inflammatory cells with a resultant reduced production of AA-derived pro-inflammatory mediators. As pro-aggregatory TXA2/prostaglandin H2 receptor antagonists in human platelets in vitro, omega-3 fatty acids reduce the risk of thrombosis by blocking the formation of thromboxane A2 (TXA2) [4].

Glaucoma

The second most common cause of blindness worldwide is glaucoma. An optical neuropathy called glaucoma is defined by a certain anatomical change in the optic nerve head that causes the vision field to gradually deteriorate. Although elevated intraocular pressure (IOP) is a major risk factor for primary open angle glaucoma (POAG), other factors—vascular insufficiency, glutamate-mediated toxicity, excessive nitric oxide (NO) generation, and oxidative stress—also have a significant impact [5].

Cod liver oil is used widely as a dietary supplement. It is abundant in important omega-3 fatty acids, including DHA and EPA, as well as vitamins A and D [5].

Because cod liver oil has a moderate amount of vitamin A and great quality of vitamin A, it’s a useful source of vitamin A supplementation. Vitamin A is an essential fat-soluble vitamin. It is required for normal functioning of growth, vision, epithelial differentiation, immunity, and reproduction. Additionally, vitamin A plays a critical function in ocular metabolism as it is necessary for the survivability of retinal pigment epithelial cells, retinal phototransduction, and the preservation of conjunctival and corneal epithelial cells. Vitamin A is necessary for the growth and differentiation of ocular epithelial cells, as well as for the preservation of conjunctival and corneal epithelial cells. It is essential for controlling the ocular surface epithelium’s synthesis of mucin, which is recognized to be a critical component of the ocular surface defense [5].

The phospholipids of cell membranes in every part of the human body, particularly in the brain, heart, retina, and testes, are concentrated sources of both EPA and DHA. Elevated IOP is the main risk factor among those implicated in the pathophysiology of glaucoma. Lowering IOP protects glaucoma progression at both the early and late phases, according to the results of a large-scale, long-term clinical investigation. The IOP is determined by the balance between aqueous humor production and outflow. Nguyen et al demonstrated that an increased consumption of omega-3 fatty acids leads to decreased IOP through an increased aqueous outflow facility [5].

 

References

  1. Tinna E., Thorhallur I., Inga T., Gunnar S., Sigurdur S., Tamara H., et al. Cod liver oil consumption at different periods of life and bone mineral density in old age. British Journal of Nutrition. 2015 [Cited 2024 June 7]; 114: 248-56. Available form: https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/cod-liver-oil-consumption-at-different-periods-of-life-and-bone-mineral-density-in-old-age/FAF8A2C658AAF93A6499FCADCF9FF4D3
  2. Charoenngam N, Shirvani A, Holick M. Vitamin D for skeletal and non-skeletal health: What we should know. J Clin Orthop Trauma. 2019 [cited 2024 June 7]; 10: 1082-93. Available form: https://www.journal-cot.com/article/S0976-5662(19)30396-0/fulltext
  3. Fatima F, Memon A, Zafar S, Amar Z, Talpur A, Hashim S, et al. Role of Cod Liver Oil in Reducing Elevated Lipid Parameters. Cureus. 2021 [cited 2024 June 7]; 13: 1-4. Available form: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8271090/
  4. Mal M, Kumar A, Meraj A, Devi A, Mañego A, Anjum Z, et al. Role of Cod Liver Oil in Preventing Myocardial Infarction. Cureus. 2021 [cited 2024 June 7]; 13: 1-5. Available form: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8324067/
  5. Huang W, Fan Q, Zhang X. Cod liver oil: a potential protective supplement for human glaucoma. International Journal Ophthalmol. 2011 [cited 2024 June 7]; 4: 648-51. Available form: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3340802/
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