Are there any side effects from taking vitamin D supplements?

When recommended doses of vitamin D are taken, side effects are uncommon, according to WebMD. However, when consumed in excessive quantities, vitamin D may cause fatigue, weakness, sleepiness, headache, loss of appetite, dry mouth, metallic taste, nausea or vomiting.

Very high intake of vitamin D sometimes leads to too much calcium in the blood, WebMD states. In people with kidney disease, this often causes atherosclerosis, or hardening of the arteries.

The recommended daily amount of vitamin D varies by age. People ages 1 to 70 and pregnant and lactating women require 600 International Units, WebMD reports. People 71 and over need 800 IU. Infants 1 year old or less need 400 IU.