“Vitamin D Sleep Experiments”, 2012 (; backlinks):
Self-experiment on vitamin D effects on sleep: harmful taken at night, no or beneficial effects when taken in the morning.
Vitamin D is a hormone endogenously created by exposure to sunlight; due to historically low outdoors activity levels, it has become a popular supplement and I use it. Some anecdotes suggest that vitamin D may have circadian and zeitgeber effects due to its origin, and is harmful to sleep when taken at night. I ran a blinded randomized self-experiment on taking vitamin D pills at bedtime. The vitamin D damaged my sleep and especially how rested I felt upon wakening, suggesting vitamin D did have a stimulating effect which obstructed sleep. I conducted a followup blinded randomized self-experiment on the logical next question: if vitamin D is a daytime cue, then would vitamin D taken in the morning show some beneficial effects? The results were inconclusive (but slightly in favor of benefits). Given the asymmetry, I suggest that vitamin D supplements should be taken only in the morning.