But it's also pretty hard to take too much of it - ref eg https://www.health.harvard.edu/staying-healthy/taking-too-mu... - and the supplement doesn't cost much at all
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?
Some people say 500 IU is enough, some say you need 4000 IU per day.
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.
https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessiona...
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).
https://www.healthline.com/nutrition/how-much-vitamin-d-is-t...
They sell 5000 IU vitamin D pills, with regular supplementation my serum levels were at the top of the range which led me to ease off.
You can take too much and there are consequences, it screws with your calcium which eventually screws with your nerve firing.
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.