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.
According to the vitamin guide on CNN Interactive's Food Central, excess amounts of vitamin C (ascorbic acid) and vitamin B5 (pantothenic acid) can cause diarrhea. Apart from the discomfort of diarrhea, overdosing on these vitamins is not fatal. Vitamin C and vitamin B5 are are water-soluble vitamins that are excreted from your body by sweat and urine. Unless recommended by a doctor or nutritionist, you should avoid megadoses of any vitamins, minerals or supplements.