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.
Symptoms of excess vitamin D consumption include muscle problems -- which can be experienced as numbness, fatigue, bone pain, loss of appetite, weight loss, extreme thirst, vomiting, diarrhea, constipation, sore eyes and itchy skin.