Vitamin D toxicity
Excess vitamin D causes hypercalcemia and soft tissue calcification.
Vitamin D toxicity, called hypervitaminosis D, occurs when there is too much vitamin D in the body. In adults, normal blood levels of 25-hydroxyvitamin D range from 20 to 50 nanograms per milliliter (ng/mL). Harmful effects are thought to start when levels exceed about 150 ng/mL, which is why the Endocrine Society recommends keeping levels below 100 ng/mL for safety.
The main problem is that excess vitamin D raises blood calcium to abnormally high levels, which can cause soft tissues like arteries and kidneys to calcify too much. Symptoms usually appear a few months after taking too much vitamin D. A mutation in the CYP24A1 gene can also cause toxicity without high oral intake, because it slows the breakdown of vitamin D. Symptoms may include dehydration, vomiting, diarrhea, decreased appetite, irritability, constipation, fatigue, muscle weakness, and insomnia.
Treatment almost always involves stopping vitamin D intake, eating a low-calcium diet, and taking corticosteroid drugs. Full recovery typically happens within a month. Bisphosphonate drugs, which slow bone breakdown, can also be used.
The U.S. National Academy of Medicine sets Tolerable Upper Intake Levels (UL) to prevent toxicity. These are not target intakes but levels above which risk increases. For both sexes, the ULs by age are: 0–6 months, 25 micrograms (mcg) per day (1000 IU); 7–12 months, 38 mcg/day (1500 IU); 1–3 years, 63 mcg/day (2500 IU); 4–8 years, 75 mcg/day (3000 IU); 9 years and older, 100 mcg/day (4000 IU); pregnant and lactating women, 100 mcg/day (4000 IU). The recommended dietary allowance is 15 mcg/day (600 IU; 800 IU for those over 70). Overdose has been seen at 1,925 mcg/day (77,000 IU). Acute overdose requires between 15,000 mcg/day (600,000 IU) and 42,000 mcg/day (1,680,000 IU) over days to months.
Some non-government authors suggest a safe upper intake of 250 mcg (10,000 IU) per day for healthy adults. Blood levels above 150 ng/mL are thought to cause adverse effects, so the Endocrine Society recommends keeping levels under 100 ng/mL.
Excessive sunlight does not cause toxicity because the skin regulates vitamin D production. During UV exposure, vitamin D precursors reach an equilibrium, and extra vitamin D is broken down. This process is less efficient in darker skin.
Quick Facts
- Field
- Endocrinology, toxicology
Facts from the source article.
Lore & Background
Vitamin D toxicity arises from excessive intake of vitamin D, leading to hypercalcemia. Symptoms include dehydration, vomiting, diarrhea, decreased appetite, irritability, constipation, fatigue, muscle weakness, and insomnia. A mutation of the CYP24A1 gene can cause toxicity without high oral intake by reducing vitamin D degradation. Treatment involves ceasing vitamin D intake, a low-calcium diet, and corticosteroid drugs, with bisphosphonate drugs also used; full recovery typically occurs within a month. The U.S. National Academy of Medicine has established Tolerable Upper Intake Levels (UL) by age, ranging from 25 μg/d for infants to 100 μg/d for adults and pregnant/lactating women. Non-government authors have suggested a safe upper intake level of 250 μg (10,000 IU) per day for healthy adults.
Reader's Guide
Vitamin D toxicity is significant because it demonstrates the narrow therapeutic window of a fat-soluble vitamin, with adverse effects occurring at blood levels above about 150 ng/mL. The condition is treatable but underscores the importance of adhering to established upper intake limits. The article notes that excessive sunlight exposure does not cause toxicity due to regulatory mechanisms in the skin, whereas oral supplementation can rapidly increase plasma calcifediol. Disputes exist regarding optimal vitamin D levels, as recommendations based on European populations may not apply to other ethnic groups; for example, Indians and Chinese have naturally low serum 25(OH)D levels despite abundant sun, and Inuit convert more vitamin D to its active form. The use of vitamin D compounds in rodenticides at concentrations millions of IU per gram highlights its toxic potential at extreme doses. The article also raises questions about cardiovascular effects, noting that dietary vitamin D may contribute to atherosclerotic calcification, with racial differences in plaque associations.
Did You Know?
- A mutation of the CYP24A1 gene can lead to vitamin D toxicity without high oral intake.
- Acute overdose requires between 600,000 IU and 1,680,000 IU per day over several days to months.
- Rodenticides use cholecalciferol at concentrations of 3,000,000 IU per gram to induce hypercalcemia.
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