Like anything…there is always a case of too much of a good thing! With all the benefits of vitamin D in the media, health authorities do want to make sure that people are aware of upper limits. The Tolerable Upper Intake Level (UL) for vitamin D daily dosing is based on studies examining the highest intake at which no adverse affects were observed on linear growth.[i] Note that the UL is defined as the highest continuing daily intake of a nutrient that is likely to pose no health risks for almost all individuals.
How much is too much? The following summarize the facts for adults:
- The upper intake level (UL) for vitamin D supplements in individuals 9 years of age and older is 4,000 IU/day [ii]
- Review of the literature shows the lowest dose of vitamin D proven to cause toxicity in adults is 40,000 IU/day for many months[iii]
- Farmers and lifeguards, who are exposed to long periods of sunlight would manufacture approximately 10,000 IU of vitamin D in their skin daily without the use of sunscreen.³
The following table summarizes the North American guidelines for infants and children[iv]:
Overall, it is best to seek individual advice from an informed healthcare profession who is familiar with vitamin D and your health status. Also, follow the directions on the label of products and notify your healthcare provider if you have concerns.
What could happen if someone takes too much vitamin D?
Vitamin D can be harmful if taken in excess. Vitamin D intoxication is extremely rare but can be caused by accidental or intentional intake of high doses of vitamin D. Most reports of vitamin D toxicity have been as a result of mistakes in vitamin D manufacturing facilities, or errors in medically dosing with prescription vitamin D. Vitamin D experts believe that the amount of vitamin D that causes vitamin D toxicity is more than 4 times the amount that adults get naturally through exposure to sunshine.
Symptoms and consequences of Vitamin D toxicity:
- High doses of vitamin D can lead to high levels of calcium in the bloodstream. This is known as hypercalcemia.
- Hypercalcemia is an elevated calcium level in the blood. (Normal range: 9-10.5 mg/dL or 2.2-2.6 mmol/L). It is usually an elevated laboratory finding with few symptoms. Therefore, people with hypercalcemia may not feel that anything is wrong and may only find out about their condition with a lab test which can be prescribed by a physician.
- Even though hypercalcemia may not have noticeable symptoms, there are important consequences that need to be considered. For example, high levels of calcium can result in anorexia, chills, constipation, confusion, depression, fever, fatigue, increased urination, nausea, pancreatitis, thirst, vomiting and weight loss.
- True vitamin D toxicity happens when high levels of calcium go undetected for a period of time, and calcium begins to build up in organs, such as the kidneys, causing renal or bladders stones.
- In order to produce hypercalcemia, most adults would have to take more than 10,000 IU daily for many months or years. Cases of hypercalcemia while taking 10,000 daily for several months have not been reported in published literature.[v]
- Most patients with vitamin D toxicity recover fully after discontinuing the vitamin D supplement and avoiding sun exposure for a certain amount of time.
[i] Vitamin D supplementation for breastfed infants 2004. Health Canada recommendation document (p3)
[ii] Institute of Medicine
[iii] Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations and safety. Am J Clin Nutr. 1999; 69; 842-856
[v] Cannell J., Hollis BW, Zasloff M, Heaney RP. Diagnosis and treatment of vitamin D deficiency. Expert Opin Pharmacother. 2008; 9(1);1-12.