Low-impedance headphones are in the range 16 to 32 ohms and high-impedance headphones are about 100-600 ohms. As the impedance of a pair of headphones increases, more voltage (at a given current) is required to drive it, and the loudness of the headphones for a given voltage decreases.
Yes, taking to much Vitamin D can cause some people to get diarrhea. Some others may experience constipation from to much Vitamin D.
Associated risks/scrutiny: Too much vitamin D may lead to vitamin D toxicity, which is a buildup of calcium in the blood, causing symptoms such as nausea, vomiting, poor appetite, constipation, weakness, confusion, heart rhythm abnormalities and kidney stones.