Cod liver oil must stay refrigerated whereas krill oil and fish oil in capsules doesn’t need refrigeration. The reason is that cod liver oil comes in a bottle and the oil surface will be exposed to air once the bottle has been opened. When highly unstable oil, like omega 3, is exposed to oxygen, oxidation will eventually occur and the oil can go rancid. The main problem with liquid fish oils and cod liver oil is that the oil may be excellent quality at the time the bottle is opened, but then the air in the bottle is “refreshed” each time a spoonful is taken.
Most laboratory tests, such as the Consumer Labs tests, are done immediately after a fresh bottle is opened, but that's not the oil the typical consumer will use. Normally cod liver oil sits up to 100 days in the refrigerator and that's the time the cod oil may turn bad. For this very reason it is recommended to buy cod liver oil, and other krill and fish oils for that matter, in small quantities (not more than a 30 day supply).
The way to counter the oxidation risk is with anti-oxidants, and the most cost effective, most commonly used anti-oxidant in fish oils is vitamin E. Consumers would think that high vitamin E is meant for them but that’s not completely true. The vitamin E is mainly added as a preservative to prevent the oil from going bad.
Krill oil has astaxanthin
Krill oil comes with its own natural preservative in the form of astaxanthin, the most powerful carotenoid anti-oxidant. Read more about astaxanthin here. Nevertheless, most krills oil also contain small amounts of added vitamin E.
Other articles in the WellWise krill oil versus cod liver oil series are:
Most laboratory tests, such as the Consumer Labs tests, are done immediately after a fresh bottle is opened, but that's not the oil the typical consumer will use. Normally cod liver oil sits up to 100 days in the refrigerator and that's the time the cod oil may turn bad. For this very reason it is recommended to buy cod liver oil, and other krill and fish oils for that matter, in small quantities (not more than a 30 day supply).
