40,000 or 50,000 units of vitamin D
Who in the world told you to take 40k IU's of vitamin D? 5k a day is enough.
Isn't vitamin D toxic at these levels? I know babies can overdose on it, not sure about adults.
Yes it can be toxic. With vitamin D supplements, everyone can potentially overdose, unlike what happens when we sunbathe.
In reality, we should not be talking so much about the amount to be taken, as the blood levels that are reached. In general, it is considered a safe level to have up to 100 ng/ml in the blood, but severe and widespread cases of hypercalcemia start at levels well above that, although there are some cases of people with a level slightly above 100 ng/ml who had several other health conditions and developed hypercalcemia. I have read a lot during the subject for several years, and accordingly I would say:
1) If you take 10,000 IU daily or less, you don't need to get blood work done.
2) If you take between 10,000 and 20,000 IU, I would go once or twice a year for a vitamin D and calcium test. Normally nothing happens with these doses but it is better to be safe.
3) If you take more than 20,000 IU daily, get in the hands of a medical professional.
There are other things that reduce the risk of developing hypercalcemia if you take doses that are considered high according to current guidelines:
1) Take your vitamin D3 with K2. Many supplements have them combined.
2) Drink enough water. 1.5 to 2 liters should be fine.
3) Don't take to much of calcium-rich products, like cheese etc.
Another thing you can do is what I do. In the winter months I take doses of 20,000 IU or sometimes more, in the spring and fall it would be between 10,000 and 20,000 and in the summer I don't usually take vitamin D supplements.
I always take it with K2 and I don't test myself anymore but in the past I did and I know that with this pattern I don't develop any health problems.