Taking supplements without assessing what your current daily intake of Vitamin D is can be dangerous; it is surprisingly easy to go over the recommended dosage, and there is such a thing as overdosing on vitamins [1]. You don't just get Vitamin D from the sun - it is also present in eggs, some seafood, and certain fortified dairy products. Because of this, you may not need to take a daily supplement at all. Programmers are at an increased risk for vitamin D deficiency, but you should ALWAYS examine your diet to assess your current vitamin D intake before deciding to take a supplement.
It's really, really hard to overdose on Vitamin D, and most researchers working on this have been taking much bigger doses than what's officially recommended. IIRC, some researchers were taking 10,000 IUs/day. Overdosing requires doses orders of magnitude bigger.
Those official levels were set to prevent people from getting rickets, NOT to prevent degenerative diseases or maintain optimum health.
In fact those official recommendations have been creeping upwards in a lot of places. Best would be to get a doctor to check your blood levels and supplement appropriately.
This will be a lot more accurate than assessing daily intake, since dose mainly correlates to time in the sun, which varies by location and time of day.
Well, I wouldn't say it's really hard to OD if one is not paying attention, although it's probably a very uncommon occurrence compared to deficiency rates. I have seen products with 50k IU available OTC and on the web, intended to be taken weekly.
One could see a scenario where this ends up getting consumed daily by mistake, and nutritionists would consider 50 000IU way to much in this case. (unless you have a specific condition, or post-op etc ad have been medicated in terms of therapy).
Try to find cases in the literature; you'll find cases of people taking orders of magnitude more than that for a month. But nothing serious from anyone taking 50k IUs/day, let alone per week.
I get your point that the studies are limited at such high doses, but Mayo clinic and various others disagree that it's non-toxic.
"Taking 50,000 international units (IU) a day of vitamin D for several months has been shown to cause toxicity" [1]
Regardless of that though, I agree that the UL is really difficult to quantify. Furthermore I'm not sure anyone could cite any article that shows a significant health benefit to supplementing above 10k vs below, hence, the rational choice would be to try stay below that.
However all of this talk about IU intake is secondary to the blood serum level. For the moment, that is the gold standard measure, until something something better comes along
Definitely agree with blood serum levels. In fact, I should get that done soon! :)
As far as really difficult, in Canada, ingesting enough pills to get to 50,000 IUs per day would be a chore. IIRC the last I checked the biggest OTC doses were 1,000 IUs. This might be different where you are.
Yeah it's definitely a good idea to inform yourself before popping a bunch of pills.
But, examining your diet is not going to help you make an informed decision in this particular instance. For example, you could have a gene that causes D malabsorption, or a specific type of gut bacteria that breaks down D3.
If you are serious about it, then a quick blood test is the best way to know. [1]
More importantly Vitamin D is tricky, because it has risks on BOTH side of the equation.
Deficiency can be very serious as well. Human biases tend towards non-action when confused or overwhelmed with information.
If anyone is interested in my data that has helped me, my blood tests are available on Google Docs[2] as well my 23andme partial genome[3]
Pretty much if you live in a northern part of the northern hemisphere (above 49 degrees latitude) you need a vitamin D supplement.
I recall reading about a researcher in Boston (I think) who said after about mid October you could be sprawled buck naked on a rooftop all day and not get enough vitamin D from (brief winter) sun exposure.
Vitamin D3 is very safe, one of the safer ones in fact. The target levels are still have a bit of controversy but safety is well documented. Taken blindly, without testing status, the conservative range is between 800iu to 2000iu daily. A weekly or monthly dose can be taken at once without issue.
[1] http://www.consumerreports.org/cro/magazine/2012/09/10-surpr...