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Vitamin D toxicity

Narinder Duggal, MD, FRCPC

Vitamin D is an important part of a healthy diet. There is a vast body of scientific evidence confirming the many health benefits of vitamin D on improving wellness ranging from bone health to strong immunity, diabetes, cardiovascular diseases, obesity and cancer. It is widely believed that the current recommendations for vitamin D intake are appropriate for preventing Rickets and Osteomalacia, but are inadequate for overall optimal health. The vitamin D intake associated with benefits other than Rickets and Osteomalacia suggests a need for supplementation and food fortification at much higher levels.^{1, 2}

Vitamin D toxicity is characterized by hypercalcemia, renal stones and renal calcification with acute kidney failure.³ The upper limit (UL) as established by the Food and Nutrition Board (FNB) for vitamin D is 50 micrograms or 2000 IU.⁴ However, a number of clinical trials, published subsequent to the establishment of this UL in 1997, support a significantly higher UL.4 There was absence of toxicity in trials that used vitamin D doses as high as 250 micrograms or 10,000 IU.^5-7

Robert Heaney, a renowned vitamin D researcher points out that achieving most benefits of vitamin D requires levels of 80 nmol/L or higher, while toxicity occurs at serum levels of 500 nmol/l or higher, which corresponds to oral intakes of 20,000-50,000IU/d for a number of years.³ He also suggests that 10,000 IU/d can be safely taken as the upper intake level.

In a clinical trial, patients with active multiple sclerosis were supplemented with progressively increasing doses of vitamin D3: from 700 to 7000 microgram/week. After a period of 28 weeks, the authors observed that serum 25(OH)D concentrations  of patients significantly improved resulting in the improvement of their disease. This data suggests that vitamin D intake beyond the current upper limit is safe by a large margin.⁸
 

In a meta-analysis of nearly 170 studies related to higher intake of vitamin D supplements, Cranney et al observed that the effect of vitamin D supplementation above current reference levels was not reported to be associated with clinically significant adverse events.⁹ The studies included in the analysis were related to all age groups; in children, women of reproductive age, postmenopausal women and elderly men.

Clinical research has clearly shown that vitamin D supplementation in the range of 1,000-2,000 IU per day is unable to restore vitamin D health in most individuals with chronic vitamin D deficiency. They need to exceed the vitamin D upper limits set by the National Academy of Sciences in order to bring the levels of 25-hydroxyvitamin D in their blood up to healthy levels.

Moreover, many studies have proven higher doses of vitamin D to be safe, without any symptom of toxicity. Stephenson et al reported a rare case of a 56-year-old woman who received 150,000 IU orally daily for 28 years without toxicity.⁴ Experts have explained the safety of higher intake of vitamin D relating it to sun exposure. The total body sun exposure for a few minutes produces vitamin D in the range of 10,000 to 20,000 IU depending upon the skin type. There has never been a case of vitamin D intoxication as a result of sun exposure.^3,10 Therefore, supplementing 10,000 IU/d of vitamin D is a safe dose to achieve the potential benefits of vitamin D in our bodies.

Many people have vitamin D deficiency or insufficiency. In order to achieve optimal levels of vitamin D in blood, a high quality supplement is available through Synergy Therapeutics Rx. Synergy Therapeutics Rx offers Vitamin D10, the only vitamin D supplement that is physician and pharmacist formulated and approved. It provides 10,000 IU of vitamin D3 in a once per day pulsed dose. Before taking a vitamin D supplement, you should obtain a 25(OH)D test, and coordinate with your physician to determine the appropriate amounts of vitamin D to ensure an optimal vitamin D level.

References:

1.    Huotari A, Herzig KH. Vitamin D and living in northern latitudes--an endemic risk area for vitamin D deficiency. Int J Circumpolar Health 2008;67(2-3):164-78. (PUBMED Abstract)
2.    Heaney RP, Davies KM, Chen TC, et al. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr 2003;77(1):204-10. (PUBMED Abstract)
3.    Heaney RP. Vitamin D: criteria for safety and efficacy. Nutr Rev 2008;66(10 Suppl 2):S178-81. (PUBMED Abstract)
4.    Stephenson DW, Peiris AN. The lack of vitamin D toxicity with megadose of daily ergocalciferol (D2) therapy: a case report and literature review. South Med J 2009;102(7):765-8. (PUBMED Abstract)
5.    Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr 1999;69(5):842-56. (PUBMED Abstract)
6.    Vieth R. Vitamin D toxicity, policy, and science. J Bone Miner Res 2007;22 Suppl 2:V64-8. (PUBMED Abstract)
7.    Vieth R. Vitamin D and cancer mini-symposium: the risk of additional vitamin D. Ann Epidemiol 2009;19(7):441-5. (PUBMED Abstract)
8.    Kimball SM, Ursell MR, O'Connor P, Vieth R. Safety of vitamin D3 in adults with multiple sclerosis. Am J Clin Nutr 2007;86(3):645-51. (PUBMED Abstract)
9.    Cranney A, Horsley T, O'Donnell S, et al. Effectiveness and safety of vitamin D in relation to bone health. Evid Rep Technol Assess (Full Rep) 2007(158):1-235. (PUBMED Abstract)
10.    Vieth R. Critique of the considerations for establishing the tolerable upper intake level for vitamin D: critical need for revision upwards. J Nutr 2006;136(4):1117-22. (PUBMED Abstract)