Side effects of vitamin D may include loss of appetite, nausea, sleepiness, weakness and dry mouth, according to WebMD. Vitamin D typically does not cause side effects unless a person takes more than the recommended amount.
Taking more than 4,000 units of vitamin D daily on an ongoing basis may cause an excessive amount of calcium in the blood, explains WebMD. A person should only take high doses of vitamin D under the direction of a healthcare provider.
Individuals with atherosclerosis, high calcium levels in the blood, hyperparathyroidism or kidney disease should be cautious about taking vitamin D, because it can raise calcium levels, according to WebMD. Others who should be cautious are those with lymphoma, sarcoidosis, tuberculosis or histoplasmosis. Vitamin D can lead to kidney stones and other problems in these health conditions.