Some people may remember Grandma always saying to take your cod liver oil. As foul- tasting and pungent as it was, Grandma was onto something. At one point, it was fairly common knowledge that a person should take cod liver oil for general health purposes, but that knowledge was lost in more recent generations, perhaps because it was so awful-tasting and how could something so unpalatable be good for you? While this may seem like rather poor rationale, perhaps they were onto something also.
Too Much Vitamin A is Toxic
It turns out that cod liver oil can actually be harmful due to toxic levels of Vitamin A. A 1998 study conducted by Swedish researchers found that hip fractures were higher in both men and women who consumed the highest amounts of Vitamin A in the form called retinol (“Serum retinol levels and risk of fracture,” New England Journal of Medicine), which turns out to be highly prevalent in cod liver oil (read more here). Beta-carotene, the precursor to Vitamin A found in green, orange (like carrots) and yellow vegetables, was not found to be associated with hip fracture.
A 2002 follow-up study at Harvard University confirmed that large amounts of Vitamin A in the form of retinol did indeed appear to be related to higher rates of hip fractures in women (“Vitamin A intake and hip fractures among postmenopausal women,” The Journal of the American Medical Association).
Other side effects of excess Vitamin A included joint aches, abdominal pains, skin rashes, mouth ulcers and hair loss (compare with fish oil side effects here). These findings later prompted the Institute of Medicine, a nonprofit policy organization specifically created to advise the nation on health and medicine, to cut their Recommended Daily Allowance (RDA) of Vitamin A for women in half.
As a result of these findings, it is strongly suggested that a person stay away from cod liver oil if the Vitamin A level is too high. Unless you are looking to get more Vitamin A and D in your diet, most people would much better off taking a highly-purified high-quality omega 3 fish oil supplement made from fish low on the food chain, such as sardines, mackerel and anchovies. The reason for such small fish is that they accumulate less toxins during their relatively short lifespans.
Vitamin A to Vitamin D Ratio is Important
However, if you insist on consuming a cod liver oil supplement, make sure that the Vitamin A to Vitamin D ratio in the supplement is less than 10:1. The less Vitamin D there is, the higher the chances of Vitamin A toxicity, and some cod liver oil supplements have astronomically high levels of 100:1!
Cod Isn’t Always Cod
To further confuse matters, in places such as Denmark, a cod liver oil product is permitted to contain other types of fish, yet still be called cod liver oil! However, because these other fish don’t contain Vitamin A & D at all, synthetic vitamins are allowed to be added to the supplement. Synthetic vitamins are generally greatly inferior to natural vitamins, and in some studies have shown to actually impair health!
However, feel free to enjoy some cod fish sticks from time to time!