Also, there is some evidence that Vitamin D supplementation at higher than natural, higher than usually recommended levels is beneficial to mental health (but not sure if the OP article confirms it)
Like most everything around vitamin D, the causality typically is backward. Vitamin D isn't improving these people's mental health, but it turns out that if you have a healthy life that involves ample outdoor activity, you are mentally healthier.
Consider migrant workers, who spend so much time under the hot sun picking veggies, what do their Vitamin D levels and other health metrics look like?
There's no way to know without testing. The optimal supplement amount for you could be zero, or it could be even more than 4000 IU per day. This depends on genetics, diet, ultraviolet light exposure, body composition, and a variety of other factors. So, the only way to be sure is to get periodic blood tests and titrate the supplements up or down to hit the target level.
If you don't want to hassle with testing then something like 600 IU will be adequate (although not necessarily optimal) for most adults. YMMV.
According to the National Academy of Medicine, formerly known as the Institute of Medicine, 4,000 IU is the safe upper level of daily vitamin D intake. However, doses up to 10,000 IU have not been shown to cause toxicity in healthy individuals (11Trusted Source, 16Trusted Source).
Vitamin D toxicity is generally caused by excessive doses of vitamin D supplements, not by diet or sun exposure (17Trusted Source, 18Trusted Source).
Although vitamin D toxicity is a very rare condition, recent increases in supplement use may lead to an increase in reported cases.
A daily intake ranging from 40,000–100,000 IU (1,000–2,500 mcg), for 1 to several months, has been shown to cause toxicity in humans (15Trusted Source, 19Trusted Source, 20Trusted Source, 21Trusted Source, 22Trusted Source).
If you look at the literature on cases of D "toxicity" (hypercalcemia), it only really occurs when people take absurd doses like 100k IU per day (often far more) for months. This usually occurs by accident, rather than someone choosing to take that much. And since D toxicity isn't reported that often, I have to assume that there are a lot of people out there unwittingly taking mega doses but without developing toxicity. But everyone thinks that high doses of D are scary because of that idiotic 4000 IU number that gets thrown around.
N=1, but I take 50k IU per day and have never had any issues. My calcium is within the normal range.
The range that is considered safe is much smaller than the range that is actually safe. It also doesn't help that there is misinformation about what "vitamin D toxicity" actually is.
Wikipedia states "Vitamin D toxicity, or hypervitaminosis D is the toxic state of an excess of vitamin D. The normal range for blood concentration is 20 to 50 nanograms per milliliter (ng/mL). However, the toxic state is known to be a value of 100 ng/ml or more in a clinical setting."
This is wrong because toxicity is not a pure function of vitamin D concentration. I'm above 100 ng/ml and yet my calcium is normal. The toxicity is purely a result of elevated calcium levels. The threshold level of D which causes this elevated level of calcium seems to vary significantly between individuals, and in any case, is much higher than the numbers that google or wikipedia gives you. At any rate the 4000 IU number is unscientific nonsense.
One of the claims is that what's considered normal range is already too low. I'm not personally equipped to tell you if that's right or wrong. But when people are suggesting to take megadoses they're coming from this angle, whether they realize it or not.