I used the Nature Made 5000IU. I took 2 per day for about 3 months and had my blood tested. It was only 49, within "normal range," but well short of the 250 I was shooting for. So I don't think the 5000IU is accurate at all. Hopefully someone knows of a supplement that is as potent as advertised because the trial and error approach takes too long.
@rokkit: 5000IU is little better than a maintenance dose. besides that, absorption depends on more than age, colour, clothing choices, sunscreen use, and location.
zinc is a factor in successful d3 absorption. if you are low in zinc too (as ms patients are known to be and as i definitely was), d3 synthesis is impaired
(and because i have my mind on it right now, with low zinc your urea cycle is also impaired, resulting in increasing ammonia levels in your blood. i have know this for a while but had no idea how serious it could get. i read yesterday that a woman who went into hospital was found to have zinc level of 7.65 umol/L and ammonia at 745 umol/L. my zinc was 8.6 umol/L when i had it tested. i shudder to think what my ammonia level must have been. the normal range for ammonia is 15-45 umol/L. !!!!!)
there is research out there that would let you calculate dose response to vit d3 over time, using your weight. when i did that early-on calculation in '06, i figured at 4000IU per day I would be 6 months getting up over 100, even.
i was not prepared for that kind of delay, so i talked to my doc and it was she who advised me to call drug info at mac. i did not give them my personal details i just asked how to get vitamin D up by 50 nmol/L quickly, and they told me. then they asked me why and when we did get into it, they said usually they would give that advice to get a patient level *up* to where mine was (low 70s nmol/L).
the 50,000 IU per day for 10 days was a quick easy fix. but with adequate zinc in my system i can't do that any more, it's dangerous. may i ask why you are shooting for 250 nmol/L by the way?