Why fear the coming of Winter in Game Of Thrones? The hypovitaminosis D hypothesis.

Background: The Game of Thrones fiction is particularly marked by an alarmist maxim, "Winter is coming", which highlights the fear of Westeros inhabitants as Winter approaches. The threat is such that Winter has been given the face of the Night King, whose progress threatens all life north of Westeros. The objective of this narrative review was to elucidate why the coming of Winter was so threatening, particularly by exploring the hypovitaminosis D hypothesis.

Methods: Three sources of information were consulted in April-June 2019, including PubMed, the fantasy novels A Song of Ice and Fire by George R.R. Martin, and the Game of Thrones Wiki.

Results: As the sun is the primary source of vitamin D, lower serum 25-hydroxyvitamin D levels are typically observed during Winter. Vitamin D regulates hundreds of genes in almost all human tissues, with relevance for several diseases. Winter-induced hypovitaminosis D may thus initiate and/or exacerbate: i) diseases such as osteopathies, viral infections, cardiovascular diseases, autoimmune diseases and cancers; ii) decline of physical abilities and skills needed for physical trades or combat; iii) decline of cognition and decision-making abilities, which are necessary to carry out the game of thrones; iv) greater mortality risk threatening all humanity.

Conclusions: If Winter comes south of the Wall, people of all ages and conditions in Westeros would be exposed to the risks induced by hypovitaminosis D. We propose that Winter, the Night King and hypovitaminosis D are one and the same danger in Game of Thrones.