Per tablespoon (13.6 g), cod liver oil contains 136% of the established daily Tolerable Upper Intake Level (UL) for Preformed Vitamin A (Retinol).[15][16] Vitamin A accumulates in the liver, and can reach harmful levels sufficient to cause hypervitaminosis A.[9] 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 such as retinol. High doses of synthetic vitamin A (retinoids) have been shown to cause birth defects.[17] A toxic dose of retinol (vitamin A) is around 25 000 IU/kg (see Retinol#Retinoid overdose (toxicity)), or the equivalent of about 1.25 kg of cod liver oil for a 50-kg person. A recent study (Cancer.org 17 July 2013) reports an increased risk of Prostate Cancer in men taking supplements with high levels of Omega-3 fatty acids.[citation needed] This would include cod liver oil.
The risks of hypervitaminosis and of exposure to environmental toxins such as mercury, polychlorinated biphenyls (PCBs), 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.[18]
A high intake of cod liver oil by pregnant women is associated with a nearly fivefold increased risk of gestational hypertension