How much vitamin d should you take in a day? is it possibel to overdose?

Vitamin D: Depends on many factors e.g. Age, amount of skin exposed to sun rays daily, use of sun blockers, time of day that skin is exposed, race, location, and other factors. The best source of vitamin d is that which your body makes from exposure of the naked skin to the sun rays. If this is not optimal then vit. D supplementation is necessary. Keep the blood level above 40 but below 90 for safety.

1000 units: Yes it is possible to overdose. Blood levels can provide an accurate assesment of how much you may need.

800-2000 units a day: Dose depends on your personal medical history. For an average healthy person, 800-1000 units of vit d2 per day is fine, for other folks with documented vit d deficiency or osteoporosis, you may need more. Note, people with medical problems like tuberculosis or sarcoidosis may be harmed by taking vit d supplements. Most experts recommend up to 2000 units a day, to avoid overdose.

800 units or so: There is not an exact known limit for vit d in adults, but too much can be toxic. This is because vit d increases calcium and phosphorus absorption, and too much calcium for example can cause constipation or kidney stones. It is not clear that everyone benefits from vitamin d supplements, but if you do take it, 800-1000 units daily seems to be plenty, and safe.