Ok 2 hours in and the main idea seems to be that there are photoreceptors deep inside the human body (including brain) that don’t make any sense at all to be there UNLESS light was being produced from within, which Kruse argues is correct and is inhibited by leptin resistance (mainly not enough direct sunlight and also too much blue light especially after sundown), so he has this Leptin prescription that will essentially repair your ability to absorb sunlight optimally:

https://jackkruse.com/my-leptin-prescription/#