Vitamin D toxicity, also referred to as vitamin D intoxication or hypervitaminosis D, is the harmful effect of too much of this vitamin in the body.
Though rare, it can be potentially dangerous, in spite of the fact that vitamin D is probably one of the least toxic fat-soluble vitamins. It can be life-threatening and can cause morbidity, if not diagnosed and treated promptly.
It leads to side effects, common of which are nausea, vomiting, weakness, and increased frequency of urination. Later, you can develop bone pain and kidney problems.
When you take in too much vitamin D, you lose the benefits of this essential vitamin. And, too much of it in the body can develop due to the intake of large doses of its supplements. Excessive exposure to sunlight or excessive intake of vitamin D foods will not cause its toxicity.
You should, therefore, know the recommended supplement limit.
Recommended intake and maximum upper intake level
The recommended daily intake depends on your age:
• For children up to age 12 months, it is 400 international units (IU) ( 10 mcg also written as μg)
• For people between the age of one year to 70 years, the daily requirement is 600 IU (15 mcg).
• For pregnant or lactating women, it is 600 IU (15 mcg)
• For people over 70 years, the requirement is 800 IU (20 mcg)
According to The U.S National Academy of Medicine, a Tolerable Upper Intake Level (UL) to protect against vitamin D toxicity has been set.
Please note that this is not the recommended intake but rather the upper limit, which if crossed, increases your risk of toxicity.
These levels are measured in micrograms (mcg or µg) and International Units (IU) where 1 µg = 40 IU and 0.025 µg = 1 IU.
The upper levels for both males and females, by age, are as follows:
• 0–6 months: 25 µg/d (1000 IU/d)
• 7–12 months: 38 µg/d (1500 IU/d)
• 1–3 years: 63 µg/d (2500 IU/d)
• 4–8 years:75 µg/d (3000 IU/d)
• 9+ years:100 µg/d (4000 IU/d)
• Pregnant and Lactating: 100 µg/d (4000 IU/d)
You are seriously at risk of overdose if you consume1,925 µg/day or 77,000 IU per day and acute overdose can develop between 15,000 µg/day and 42,000 µg/d (600,000 IU per day to 1,680,000 IU per day) over a period of several days to months.
Normal, low, and toxic levels of vitamin D
The vitamin D test is performed on your blood sample to determine its levels in your blood.
• Generally, normal values are 75-100 nmol/L (30-40 ng/ml).
• Vitamin D deficiency is defined when serum hydroxyvitamin D levels are less than 50nmol/L (20 ng/ml), and
• You are said to have insufficiency when your levels are at 50-75 nmol/L (20-30 ng/ml).
• Levels above 125 nmol/L (50 ng/mL) are too high and may cause toxicity and health problems.
What Causes Vitamin D Toxicity (VDT)?
Exogenous vitamin D toxicity is almost always the result of taking too much of supplements and is associated with hypercalcemia. Your body regulates how much of it your skin produces from the sunlight and therefore, you will not develop toxicity from sunlight exposure. And, foods generally contain small amounts of vitamin D and you cannot get too much of it from food.
Those taking supplements to address vitamin D insufficiency or deficiency may likely go overboard with the dose to seek more benefits. Taking its supplements for a prolonged period in doses higher than 4000 IU (100 mcg) daily can be unsafe and may cause very high levels of calcium in the blood. If this continues over a period, you are likely to develop side effects.
According to the Mayo Clinic, taking 60,000 international units (IU) every day for several months can lead to toxicity.
The U.S. Recommended Dietary Allowance (RDA) for most adults is 600 IU of vitamin D a day. If you are deficient, then, doses higher than the RDA may be prescribed by your doctor. However, these are given only for a specified time frame under medical guidance with due monitoring of the blood levels.
The Endocrine Society suggests that all people on high doses of supplements monitor serum levels of 25-hydroxy vitamin D and calcium.
Endogenous VDT may develop due to
• too much production of 1,25(OH)2D, which can occur in granulomatous disorders and in some lymphomas.
• reduced deprivation of 1,25(OH)2D such as in idiopathic infantile hypercalcemia.
• excessive production of this metabolite can occur in congenital disorders, such as Williams–Beuren syndrome.
• hypersensitivity to vitamin D.
Side effects or symptoms of too much Vitamin D
Too much vitamin D in the body can cause an excessive build-up of calcium in the blood. This is called hypercalcemia and is the clinical presentation of vitamin D toxicity. Hypercalcemia results in over-calcification (too much calcium buildup) in the bones, heart, kidneys, and soft tissues.
The side effects or symptoms of this toxicity appear several months after its excessive doses have been taken. They include:
• Loss of appetite
• Diarrhea or constipation
• Muscle weakness
• Increased frequency of urination
• High blood pressure
If you experience any of these side effects after taking its supplements, you must talk to your health provider giving him the history of the medications/supplements you have been taking.
He may have your blood tested for vitamin d blood serum levels. Serum 25-hydroxyvitamin D [25(OH)D] levels higher than 150 ng/ml (375 nmol/l) are indicative of toxicity caused by taking too much of its supplements.
Long-term effects of vitamin D toxicity
Vitamin D toxicity can cause other complications, including kidney and bone problems. Too much of this vitamin leads to excessive calcium in the blood. This is called hypercalcemia.
Vitamin D toxicity is usually reversible, but severe cases may eventually lead to kidney failure and calcification of the arteries.
Acute renal failure can be treated with hemodialysis, and rarely is the renal damage due to toxicity permanent.
Hypercalcemia, a fallout of vitamin D intoxication is a medical emergency and must be treated as such once the serum calcium is determined to be above 14 mg/dL.
Hypercalcemia is a condition in which the calcium level in your blood is above normal. Normal calcium levels are between 8.8mg/dL to 10.8mg/dL.
Calcium serum level between 10.5 to 13.9 mg/dL is classified as mild to moderate, but levels between 14.0 and 16.0 mg/dL are considered a hypercalcemia emergency.
Some signs of hypercalcemia include:
• Loss of appetite
• Excessive thirst
• Frequent urination
• Memory loss
How is vitamin D toxicity diagnosed?
Vitamin D toxicity can be diagnosed clinically through the history of the patient’s supplementation of this vitamin and clinical symptoms.
Laboratory evaluation includes checking blood and urine, which will show:
- Elevated blood levels of vitamin D
- Elevated serum calcium (often greater than 11 mg/dL)
- Elevated free or ionized calcium,
- Hypercalciuria is defined as a daily urinary excretion of more than 4 mg calcium/kg body weight.
- Parathyroid hormone (PTH) levels in the blood would be suppressed
- Bone X-rays to determine if there’s any significant bone loss
Clinical treatment of vitamin D toxicity begins with stopping all vitamin D and calcium supplements and restricting foods that contain these nutrients. The main focus is on lowering calcium levels in the blood.
• Stop all vitamin D and calcium supplements.
• Avoid excessive bed rest to prevent hypercalcemia that can be caused by inactivity.
• Isotonic saline helps to treat dehydration caused by any kidney problems.
• Severe hypercalcemia due to severe toxicity can be treated with intravenous calcitonin and bisphosphonates. However, calcium levels should be regularly checked during the use of these medications to check for their efficacy.
• Intravenous steroids lower calcium levels in the blood. They act by reducing its absorption in the intestines and increasing its excretion through urine. However, the regular use of steroids for this toxicity is controversial.
• Hemodialysis may be indicated in rare cases to eliminate calcium where calcium excretion is impaired due to significant kidney damage.
How long does it take to recover from vitamin D toxicity?
Hypercalcemia is the clinical manifestation of too much vitamin D in the body, which develops due to regularly taking high amounts of its supplements.
This fat-soluble vitamin accumulates in the body fat and is slowly released into the blood and therefore hypercalcemia may take a few months to resolve.