Just a caveat on the use of cod liver oil as a source of Vitamin D:
Cod liver oil has large amounts of Viramin A in the form of retinol which can be toxic. Since the recommendations for Vitamin D are now 5 to 25 times the original RDA, cod liver oil could propose a problem without taking into account the toxicity level for retinol.
[quote author=Wikipedia]Retinoid overdose (toxicity)
see Hypervitaminosis A for details
The Tolerable Upper Intake Level (UL) for vitamin A, for a 25-year old male, is 3,000 micrograms/day, or about 10,000 IU.
Too much vitamin A in retinoid form can be harmful or fatal, resulting in what is known as hypervitaminosis A. The body converts the dimerized form, carotene, into vitamin A as it is needed, therefore high levels of carotene are not toxic compared to the ester (animal) forms. The livers of certain animals, especially those adapted to polar environments, often contain amounts of vitamin A that would be toxic to humans. Thus, vitamin A toxicity is typically reported in Arctic explorers and people taking large doses of synthetic vitamin A. The first documented death due to vitamin A poisoning was Xavier Mertz, a Swiss scientist who died in January 1913 on an Antarctic expedition that had lost its food supplies and fell to eating its sled dogs. Mertz consumed lethal amounts of vitamin A by eating the dogs' livers.[8]
Vitamin A toxicity occurs when an individual ingests vitamin A in large amounts more than the daily recommended value in the threshold of 25,000IU/Kg or more. Often, the individual consumes about 3-4 times the RDA's specification [9] Toxicity of vitamin A is believed to be associated with the intervention methods used to upgrade vitamin A levels in the body such as food modification, fortification and supplementation, all of which are employed to combat vitamin A deficiency [10] Toxicity is classified into two categories: Acute and chronic toxicities. The former occurs few hours or days after ingestion of large amounts of vitamin A accidentally or via inappropriate therapy. The later toxicity (Chronic) takes place when about 25,000IU/Kg or more of vitamin A is consumed for a prolonged period of time. Symptoms associated with both toxicities include, but not limited to nausea, blurred vision, fatigue, weight-loss, menstrual abnormalities etc.[11]
If eaten in one meal, 30 to 90 grams of polar bear liver is enough to kill a human being, or to make even sled dogs very ill.[12]
Excess vitamin A has also been suspected to be a contributor to osteoporosis. This seems to happen at much lower doses than those required to induce acute intoxication. Only preformed vitamin A can cause these problems, because the conversion of carotenoids into vitamin A is downregulated when physiological requirements are met. An excessive uptake of carotenoids can, however, cause carotenosis.
The carotenoid beta carotene was interestingly associated with an increase in lung cancer when it was studied in a lung cancer prevention trial in male smokers. In non-smokers, the opposite effect has been noted.
Excess preformed vitamin A during early pregnancy has also been associated with a significant increase in birth defects.[13] These defects may be severe, even life-threatening. Even twice the daily recommended amount can cause severe birth defects.[14] The FDA currently recommends that pregnant women get their Vitamin A from foods containing beta carotene and that they should ensure that they consume no more than 5,000 IU of preformed Vitamin A (if any) per day. Although Vitamin A is necessary for fetal development, most women carry stores of Vitamin A in their fat cells, so oversupplementation should be strictly avoided.
A review of all randomized controlled trials in the scientific literature by the Cochrane Collaboration published in JAMA in 2007 found that supplementation with beta-carotene or vitamin increased mortality by 5% and 16%, respectively.[15]
Contrary to earlier observations, recent studies emerging from some developing countries(India, Bangladesh and Indonesia) have strongly suggested that dosing expectant mothers in the population in which vitamin A deficiency is common and maternal mortality is high can greatly reduce maternal mortality ratio [16] Similarly, dosing newborn infants with 50,000IU(15 mg) of vitamin A within 2 days of birth, can significantly reduce neonatal mortality [17][/quote]
Because cod liver oil has a very high level of Vitamin A, it is possible to exceed the Recommended Dietary Allowance (RDA) of vitamin A. Vitamin A accumulates in body fat, and can reach harmful levels sufficient to cause hypervitaminosis A.[17] Pregnant women may want to consider consulting a doctor when taking cod liver oil because of the high amount of natural forms of Vitamin A (Retinol). High doses of synthetic Vitamin A (Retinoids) have been shown to cause birth defects.[18]
The risks of hypervitaminosis and of exposure to environmental toxins such as mercury, polychlorinated biphenyls, dioxins, and other contaminants, are reduced when purification processes are applied to produce refined fish-oil products, which consequently contain raised levels of omega-3 fatty acids, such as EPA and DHA.[19]
A high intake of cod liver oil by pregnant women is associated with a nearly five-fold increased risk of gestational hypertension,[20] although this study did not control for mercury, which can be present in harmful amounts in fish[19] and which is another cause of hypertension.[21]
Some urge caution when taking cod liver oil and other fish-based supplements since they may contain elevated levels of toxins such as mercury and PCBs found in fish.[19] Some supplement companies regularly test cod liver oil for purity, while others do not. Consumerlab.com tested 44 fish and cod liver oil supplements and found that all were free of detectable levels of mercury.[22]
All things considered, cod liver oil is still an excellent supplement.
