It is often thought that cod liver oil and fish oil are the same thing, and they are often marketed by companies as the same thing; but they are not. Fish oils are derived from the skin of a variety of types of fish, where as cod liver oil is obviously oil from the liver of cod.
Vitamin A & D
Large fish, which are high up the food chain are usually higher in bio-accumulative toxins such as methylmercury and PCBs. Depending on where the cod is sourced from, cod liver oil may contain higher levels of these toxins. This is why it is important to ensure you know where your product is sourced from. Fish oils often contain less of these toxins than cod liver oil, but there is a lot of variation depending on where they are sourced from, so weather you have fish oils or cod liver oils you should find out if they are low in these toxins. If you are using a fish oil, make sure it is made from small fish.
Which is best?
It is impossible to say which is the best supplement as it ultimately depends on the sourcing, manufacturing, and for fish oils, the quantities of oils used. However, if the quality and processing is the same cod liver oil would be my preferred choice as it contains vitamin A and D, has much more research supporting its benefits, and is consistent in its nutritional make up. I’ve compiled a comparison of some popular cod liver oils and fish oil, which you might also find useful.
Image courtesy of ellie-yannis