The ancient Norse Vikings were consumers of liver oils, in particular codfish liver oil, Chimaera monstrosa (ratfish) liver oil, and shark liver oils. Codfish liver oil was used for the maintenance of general health, particularly during the cold months ending in "r". These months are characterised by low sunlight intensity and an increased risk of hypovitaminosis D (vitamin D deficiency). Such a deficiency can have tragic consequences in light of the fact that vitamin D has been shown to play very important roles in brain, heart, immune system and bone health. During the winter months in the northern climes, people are unlikely to be able to synthesise enough vitamin D via ultraviolet-B rays from sunlight striking the skin and triggering vitamin D synthesis. So having a diet that is rich in oily fish, and consuming fish liver oils, would have given the Nordic people a natural supply of this all important vitamin during the winter months.