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.
There is such a thing as too much vitamin D. Vitamin D in excess of 4,000 IU can cause side effects such as anorexia, excessive urine output, heart arrhythmias, and kidney stones. Excess vitamin D is usually caused by taking too much in the form of supplements.