Vitamin D needs vary. Average daily recommended amounts are usually in either micrograms (mcg) or International Units (IU). National Institutes of Health states that people between the ages of one to 70 need at least 600 IU (15 mcg). On your 71st birthday, that recommended amount increases to 800 IU (20 mcg). This is because your skin can’t make vitamin D as efficiently when you are older.
Overdoing it on vitamin D can result in toxicity that brings nausea, vomiting, weakness, and weight loss. To avoid this, the daily upper limit is set at 2,500 to 3,000 IU (63 to 75 mcg) for children aged one to eight, and 4000 IU (100 mcg) for children older than nine and adults. Most of the time, excessive vitamin D comes from supplementation, as our body limits the amount of vitamin D produced even when out in the sun for long periods of time.
The best way to measure the amount of vitamin D in your body is to get a blood test. Levels that fall below 30 mmol/L (nanomoles per liter) are much too low for bone or overall health, and levels above 125 nmol/L are too high. A sufficient level for most people is 50 nmol/L or above.