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Vitamin D Side Effects

An increasing number of specialists are confident that vitamin D side effects will not occur with intake less than 10,000 IU daily-except for people who are hypersensitive because of certain medical conditions.

There is significant debate over optimal vitamin D dosage. But many experts now believe that there are no vitamin D side effects with intakes of less than 10,000 daily... unless there is a specific medical condition where vitamin D supplements are contraindicated. This is quite a change from previous warnings that intake over 2,000 IU may be toxic. Here is what authorities are now saying about the safety of vitamin D supplements.


The U.S. National Osteoporosis Foundation (NOF) warns that very high doses of vitamin D can cause kidney stones and other kidney problems, which may then lead to bone loss. But it acknowledges that it is difficult to get too much vitamin D unless a person is taking a prescription dose of the vitamin.


The Vitamin D Council argues that the skin produces approximately 10,000 IU vitamin D in response to 20–30 minutes of exposure to the sun in the summer and that there is no research showing that intake below this level is toxic. One of the foremost vitamin D experts, Doctor R. Vieth, argues that toxicity probably begins after long-term daily consumption of approximately 40,000 IU/day. (Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentration and safety. Am J Clin Nutr. 1999; 69:842-56)


Vitamin D hypersensitivity is rare but may cause vitamin D side effects in the form of high blood calcium or hypercalcaemia. Some diseases that may cause this sensitivity include:

  • Hyperparathyroidism
  • Granulomatous diseases such as sarcoidosis, granulomatous TB, oat cell carcinoma of the lung, and non-Hodgkin's lymphoma
  • Occult cancers which are of an unknown origin

People who are suffering from these diseases should seek a physician's advice before beginning a Vitamin D supplement program. Regular vitamin D blood tests are the best way to monitor vitamin D levels and supplement needs.


Humans make at least 10,000 units of vitamin D within 30 minutes of full body exposure to the sun. Research also indicates that healthy humans use about 4,000 IU of vitamin D a day. (Heaney R, Davies K, Chen T, Holick M, Barger-Lux MJ. Human serum 25 hydroxycholecalciferal response to extended oral dosing with cholecalciferol. Am J clin Nutr. 2003; 77: 204-10)

Since vitamin D is stored in the body for about 60 days and people north of latitude 42 (Boston, Rome or Beijing) cannot get enough of the “sunshine vitamin” during the winter months... many health care providers are less concerned about vitamin D side effects than vitamin D deficiency. Recent studies have shown that over 70% of North Americans are vitamin D deficient for at least part of the year. Many osteoporosis experts now recommend a vitamin D dosage of 4-5,000 IU during the winter for people living in northern regions. The best way to assess the effectiveness of a supplement is to have a vitamin D blood test in the middle of winter when blood levels are at their lowest. Maintaining blood levels throughout the year will assist calcium absorption and discourage bone loss.

For more information on affordable supplements that are believed to be free of vitamin D side effects... visit Vitamin D Dosage.