Greg Harrington left a comment on an earlier post:
I have had very similar results [fall asleep more easily] from first-thing in morning D3.(NOTE: I have great flexibility in my schedule — I can sleep/awake whenever I want — so I have been most focused on “restful” sleeping.) Differences: (a) My pre-D3 issue was restless sleep (waking up frequently), not failure to fall asleep. (b) The effect of sleeping all the way through the night was definitely immediate–very first night. (c) Also, most days I also wake up feeling more “rejuvenated”. This is not 100% though.
I asked him for details.
Tell me about yourself.
I’ve lived Austin,TX since 07/2011. Kansas City, MO before that. I’m a software programmer. 6′ 3″. 210 lbs. (White male, mostly German, but completely European descent.)
How did you want to improve your sleep?
I want to sleep through the night without waking up 3-6 times in a 6-9 hour sleep. This problem has lasted for 2-3 years. It sort of crept up on me. I go to sleep between midnight and 2 am.
How much D3 do you take? At what time?
I take 50,000 IU between 8 and 9 am. If I forget or wake up later, I don’t take it. This is the product I take: Bio-Tech D3 in 50,000 IU capsules.
Why 50k? It was available on Amazon, and I calculated that to be what you’d get from 75-90 minutes of full-body sunlight. Thinking about Paleo lifestyle…that seemed reasonable. This is a LOT more than most SE people are taking but I wanted to maximize the effect! 
Any effects of D3 on something other than sleep?
I often waking up feeling more rested/rejuvenated. But not every day. I tend to feel tired between 11 pm and midnight.
What happened when you started taking D3 in the morning?
50000 IU seems like way too much to take on a daily basis. (I’ve never seen anyone recommend more than 5K to 10K per day.) I would recommend that this person get his blood levels checked and make sure they are not too high. Otherwise serious complications could occur.
Some recommend taking 50k once per week. IMO, if you’re taking 3k or more per day get a blood test. Do some research and pick a target level, mine is 100 nmol/L (40 ng/ml), then retest to monitor progress. The units differ according to your location. In Canada our tests are in nmol/L in the USA it is usually ng/ml.
Making vitamin D by exposing skin to sunlight creates a create negative feedback–the skin darkens and makes less vitamin D, so no one is getting 50000 units of vitamin D on a daily basis from sunlight. Wrong assumption, but good guess. Complications of high vitamin D include abnormal bone formation, kidney stones and possibly brain function.
50,000 a week for 8-12 weeks is the medical regimen for true deficiency, then the replacement is based more on geographic latitude than anything else.
I’m wondering if Greg Harrington took the negative feedback effect into account when he computed how much d-vitamin is created from 75-90minutes fullbody daylight. The body has a negative feedback system which cuts down d-vitamin production after some or enough has been produced. I’ve once heard it said that it only takes 15 minutes sunlight to reach that limit for white people. I tried confirming this number by asking Google + Wikipedia, but none made we wiser. But the negative feedback system definitely exists.
Huhm.. your body can only keep around 200,000 IU total. Taking 50k IU daily is too much, as it uses only about 5k per day.