Is there any reliable vitamin D recommendation for adults?

In fact, the key of vitamin D supplementation is not vitamin D, but other trace elements.

Vitamin D can promote the absorption of calcium in the small intestine, so most vitamin D supplements are to supplement calcium. But the focus of calcium supplement is not only calcium itself, but also magnesium, manganese, zinc, copper and vitamin D.

It's like building a house. Can bricks alone build a house? Don't cover it well. It also needs cement, sand, steel, concrete and other materials. The effect of calcium and vitamin D alone is very limited, and the absorption rate and utilization rate of calcium into the body is another matter. Assuming that the calcium absorption rate and utilization rate of your supplement are only 10% respectively, isn't the calcium you supplement used by the human body only 1%? Then you can supplement loneliness and psychological comfort by calcium, right? In order to improve the absorption and utilization rate of calcium, the first thing to see is what calcium you supplement and how high the calcium content is (calcium carbonate is the highest calcium content). Second, whether there are substances that can improve the absorption and utilization of calcium (such as alfalfa). So the focus of calcium is not only on calcium itself!

To sum up, a good calcium tablet or vitamin D must have the following points:
1. The best calcium supplement is calcium carbonate.
2. It also contains calcium, magnesium, manganese, zinc, copper and vitamin D.
3. There are substances to improve calcium absorption and utilization.