Kim Øyhus, a programmer who lives in Norway, writes:
Each midwinter and summer I tend to lose my feeling of when it is day or night, especially if I am in the northern parts of Norway, or if the weather is dark clouds for a long time, which often happens. So sorry, no statistics, just my sense of being unhinged from the diurnal cycle.
Taking 1-2 spoons [= 7-14 ml] of cod liver oil in the morning [7-9 am] got me back to this rhythm in about 3-5 hours. It even works for fixing my diurnal rhythm after partying to sunrise, but only after a days rest.
Is this due to Vitamin D3? (I have collected many examples of Vitamin D3 in the morning improving sleep.) Quite possibly. Cod liver oil contains Vitamin D3. When taking a Vitamin D3 supplement, the minimum dose needed to see the effect, based on the examples I’ve collected, seems to be about 1000 IU. I didn’t notice anything when I took 2000 IU. The effect first appeared at a dose of 4000 IU and was a bit larger at 6000 IU. Kim is taking 600-1100 IU of Vitamin D3, so that is consistent with the Vitamin D3 in the cod liver oil being the source of the effect.