Grade 8 English grammar. After the comma, the next word is “which;” which there refers to the word before the comma which is “sunlight.” So the author of the article, who , I suppose make his living by writing, is saying that sunlight is transported through the skin and taken to the liver, etc., etc. It is an exceedingly poorly written sentence. BTW, the rest of the article is barely above that level of incompetence.
There is a lot of poor writing and poor editing in many articles that appear on the internet.