Production
Fish oil is derived from mostly fatty, cold water fish such as menhaden, sardines, mackerel, cod, and salmon and during the processing of the fish the oil is extracted in order to produce supplements. However, the toxins that were in the fish also stay in the oil. Some of these toxins include peroxides, PCBs, dioxins, mercury, and over 200 additional pollutants. Even if consumed in small amounts, these toxins can cause some health problems which are why it is essential to pick a fish oil that has been molecularly distilled in order to remove toxins. Only the supplements that have been tested independently for purity are guaranteed as safe.
Freshness is another concern when consuming this oil. Fish oil production that is oxygen free distills values of peroxide. When there is no peroxide in the oil that can be measured there is no chance it will have oxidation which can significantly decrease the overall efficacy and freshness. Freshness in this type of oil is essential because supplements that are not fresh sometimes have a fishy taste and smell and can cause indigestion and if the oil is fresh it prevents the formation of free radicals.