I know Robin Barooah from Quantified Self meetups. When I learned he had started taking Vitamin D3 early in the morning, I asked him what happened:
I’ve been taking it since December 20. I initially thought of trying it immediately on my return from London because I thought that it might help to reduce jet lag, given its apparent coupling with the circadian rhythm.
It didn’t seem to have a dramatic effect on my jet lag – which was as bad as I usually experience it for about the same number of days (around 3-4). However it had a very pronounced effect on my general energy levels. At first I was almost hyperactive, yet my concentration was good. I was using 5000 IU per day, at 7:30 am. The hyperactive feeling subsided but the dramatic improvement of my energy levels (and increased concentration) continued until I decided to reduce the dose to 2000 or 3000 IU per day [from 5000 IU/day]. My mood has improved too, although I think indirectly though feeling more capable and productive.
I decided to reduce the dose because I was concerned that my sleep wasn’t noticeably better than before taking the D3, and might have been worse. Reducing the dose caused a huge reduction in my energy levels and concentration, and no improvement in sleep. After a week of that I went back to the 5000 IU dose, and again am very happy with the effects. The improvement in sustained concentration is so dramatic that it’s disturbing to think of how much this could have changed my life had I been using it for years (assuming the effect lasts).
It’s possible that my sleep quality has improved in some way that isn’t reflected in my subjective experience of sleeping, and this has caused the improved energy and concentration. I am sleeping about the same length of time, and waking up in the night just as often and feeling about as rested as before I started (which is not quite as rested as I’d like to feel, despite having a lot of energy). I am not taking a multivitamin, so it’s also possible that I’m not getting all of the possible benefit.
Without doubt, this is one of the most effective things I’ve ever tried.
Emphasis added. He takes Now Foods Vitamin D3 (easy to buy on Amazon), the 5000 IU and 1000 IU softgels. He also said:
I used to get quite severe tiredness (enough to need to lie down) at numerous times during the day. Now I seem to get tired just a little in the afternoon, and then progressively so into the evening. There’s a very distinct slowdown in my energy that happens very obviously around 5pm, which is coincidentally around dusk here at the moment.
I have noticed something similar. Before Vitamin D3 early in the morning, I used to get really tired around 10 am. Enough to make me lie down. This happened on more than half of all days. Now that I am taking a lot of D3 (8000 or 10000 IU) first thing in the morning (8 or 9 am) it doesn’t happen at all. (I may eventually go down to a lower dose, such as 5000 IU/day.)