Vitamin D is an essential nutrient that plays many important roles in the body. It helps regulate calcium and phosphate levels to maintain healthy bones and teeth. Vitamin D also supports immune, brain, and nervous system function. While vitamin D deficiency is common, taking too much vitamin D can also be harmful. This article will examine how much vitamin D is too much, with a focus on the tolerable upper intake level and potential toxicity in milligrams (mg).
What are the recommended daily intakes for vitamin D?
The recommended dietary allowance (RDA) for vitamin D is:
- 15 mcg (600 IU) per day for adults up to age 70
- 20 mcg (800 IU) per day for adults over 70
The RDA is the amount that meets the needs of about 97% of people. Many experts suggest that these RDAs are too low, and that optimal vitamin D intakes may be 2-3 times higher than the current RDAs at around 30-60 mcg (1200-2400 IU) per day. Groups at higher risk of vitamin D deficiency, such as those with little sun exposure, dark skin, obesity, malabsorption disorders, or on certain medications may require more.
What is the tolerable upper intake level for vitamin D?
The tolerable upper intake level (UL) for vitamin D represents the maximum daily amount that is likely to pose no risk of adverse health effects for most people. The UL is not meant to be a recommended intake – it is simply the level above which adverse effects may occur.
The UL for vitamin D is as follows:
- 100 mcg (4000 IU) per day for adults up to age 70
- 75 mcg (3000 IU) per day for adults over 70
This UL is based on the increased risk of hypercalcemia (high blood calcium levels) with excessive vitamin D intakes for prolonged periods. The UL does not apply to supplemental vitamin D used for short periods under medical supervision.
How much is too much vitamin D in mg?
Since vitamin D is measured in international units (IUs) or micrograms (mcg), it needs to be converted to milligrams (mg) to determine potential toxicity thresholds.
Here is the conversion:
- 1 IU of vitamin D = 0.025 mcg
- 1 mcg of vitamin D = 40 IU
- 1 mcg of vitamin D = 0.00004 mg
Based on these conversions:
- The UL of 4000 IU (100 mcg) equals 4 mg of vitamin D
- The UL of 3000 IU (75 mcg) equals 3 mg of vitamin D for adults over 70
Therefore, vitamin D intakes exceeding 4 mg per day for most adults and 3 mg per day for adults over 70 would be considered potentially excessive.
However, toxicity thresholds based on megadoses used for medical treatments are much higher, in the range of 60-100 mg per day for extended periods.
What are the symptoms of vitamin D toxicity?
Consuming vitamin D regularly in excess of the UL may lead to vitamin D toxicity or hypervitaminosis D. Symptoms include:
- Nausea, vomiting, poor appetite
- Increased urination and thirst
- Constipation
- Weight loss
- Confusion
- Irregular heartbeats
- Deposits of calcium and phosphate in soft tissues
More serious long-term complications can include kidney stones, high blood pressure, and damage to the heart and blood vessels. Symptoms of toxicity often develop slowly over months to years of excessive intakes. Milder symptoms may occur at intakes closer to the UL before more serious effects are seen at very high intakes.
What causes vitamin D toxicity?
Potential causes of vitamin D toxicity include:
- Taking vitamin D supplements long-term in excess of the UL – 4000 IU (100 mcg) per day is the limit for most adults
- Taking a very large one-time dose of vitamin D, usually in order to treat a deficiency
- Taking a prescription vitamin D analogue like calcitriol or alfacalcidol
- Errors in prescription doses or formulations
- Eating foods or using cosmetics extremely high in vitamin D, though this is less likely
- Some underlying health conditions that increase sensitivity to vitamin D
- Certain medications that interfere with vitamin D metabolism
Those with conditions affecting vitamin D absorption like Crohn’s disease or cystic fibrosis may be at higher risk of toxicity at lower intakes. Individual tolerance also varies based on genetics, body size, and other factors.
Who is at risk of vitamin D toxicity?
The following groups may be at higher risk of vitamin D toxicity:
- People taking high dose vitamin D supplements long-term without medical oversight
- Individuals with underlying health conditions like primary hyperparathyroidism or sarcoidosis
- Those on certain medications that affect vitamin D metabolism, like anticonvulsants or glucocorticoids
- People with granulomatous disorders that increase sensitivity to vitamin D
- Individuals who consume a lot of foods or use cosmetics very high in vitamin D
- Infants given high dose supplements meant for adults
Toxicity is more likely with long-term intakes consistently over the UL, rather than a single high dose. Those with normal vitamin D metabolism typically tolerate occasional high doses without adverse effects. But some are sensitive even at lower doses, so intakes substantially above the RDA warrant caution without blood level monitoring.
Can you get too much vitamin D from sun exposure?
It’s extremely rare to develop vitamin D toxicity from excessive sun exposure alone. The skin has mechanisms that slow vitamin D production and degrade excess vitamin D from sunlight to prevent toxicity.
However, extremely high sun exposure may very rarely cause toxicity in unusual circumstances, such as over an entire summer of extensive sunbathing. Fair-skinned individuals are likely more susceptible. But routine sun exposure does not provide intakes anywhere near toxicity levels or require limiting time outdoors.
Can you get too much vitamin D from food sources?
It’s also very rare to get excessive vitamin D solely from dietary sources. Most foods are naturally low in vitamin D, aside from some fatty fish and fish liver oils.
Estimated intakes from food alone are typically 100-288 IU (2.5-7 mcg) per day at most, well below the UL. Eating several servings of fish like salmon or mackerel daily or taking spoonfuls of cod liver oil can provide excessive intakes over 2000 IU (50 mcg) per day if sustained long-term. But toxicity solely from foods is unlikely.
Fortified foods like milk, juices, yogurt, and cereals contain vitamin D, but usually no more than 100 IU (2.5mcg) per serving. Even if consumed in large amounts, fortified foods are unlikely to cause excessive intakes on their own. But they can contribute to total intake above the UL if paired with supplements.
What are safe upper limits for vitamin D supplements?
The Institute of Medicine’s UL of 4000 IU (100 mcg) per day for adults sets a safe upper limit for vitamin D supplements. While the RDA is only 600-800 IU (15-20 mcg), many experts recommend supplements of 1000-2000 IU (25-50 mcg) daily for optimal intakes.
So for supplements, intakes up to 2000-4000 IU (50-100 mcg) per day are likely safe for most adults based on current evidence. Some organizations suggest a more conservative upper limit of 1000 IU (25 mcg) for infants and 2000 IU (50 mcg) for children to reduce risks.
Therapeutic doses under medical care may be much higher, even 50,000 IU (1250 mcg) weekly. But high-dose therapy should always involve blood level monitoring and be under a doctor’s supervision.
Should I get my vitamin D blood levels tested?
Getting baseline 25-hydroxyvitamin D blood levels tested can help determine your individual vitamin D needs. Optimal levels are generally considered to be between 30-60 ng/ml. Those under 30 ng/ml should supplement with 1000-4000 IU (25-100 mcg) per day based on their starting level until they reach the optimal range.
Periodic retesting is prudent if supplementing with higher doses over 2000 IU (50 mcg) per day for extended periods to ensure levels remain within an appropriate range. Those with medical conditions, on relevant medications, or with very limited sun exposure should have levels monitored regularly.
If levels exceed 100-150 ng/ml, reduce supplemental vitamin D to bring your level back down. Anyone with hypercalcemia symptoms should have their vitamin D and calcium levels tested promptly.
Can you take too much vitamin D for a short time?
The UL applies to sustained long-term daily intakes, as toxicity is most likely from excessive vitamin D buildup over months to years. Taking doses above the UL for short periods is typically well-tolerated.
Many doctors prescribe short-term very high doses up to 50,000 IU (1250 mcg) weekly or even 600,000 IU (15,000 mcg) as a single dose to quickly boost low vitamin D levels. However, medical guidance and retesting levels after treatment is important.
Occasionally supplementing with 10,000-25,000 IU (250-625 mcg) per week for a month or two to raise low levels is likely safe for most. But regular intakes consistently exceeding 4000 IU (100 mcg) per day long-term is not recommended without testing vitamin D status.
Is it possible to take a toxic single dose of vitamin D?
It would take an extraordinarily high single dose of vitamin D to cause immediate toxicity. Doses below 200,000 IU (5000 mcg) are unlikely to cause toxicity after one-time intake.
However, single doses above 600,000 IU (15,000 mcg) may raise blood calcium and vitamin D levels enough to cause symptoms. Extreme single doses above 2 million IU (50,000 mcg) could potentially become dangerous depending on the individual.
Acute toxicity is most likely from errors like misplacing a decimal point on prescription strengths or taking tablespoons instead of teaspoons of concentrated supplements. Very large correctly dosed single intakes under medical care require blood testing after treatment.
Can you recover from vitamin D toxicity?
Fortunately, vitamin D toxicity is treatable and reversible in most cases if addressed promptly before permanent damage occurs. However, long-standing and severe toxicity can cause irreversible organ damage.
Stopping supplemental vitamin D allows blood levels to slowly normalize over time. Drinking plenty of fluids helps flush out excess. Certain medications may be used to help lower calcium and normalize vitamin D metabolism. Those with kidney or heart damage require close ongoing monitoring.
Prevention is ideal by having blood levels checked routinely if supplementing with high doses of vitamin D or having a medical condition that increases risk. Don’t exceed the UL of 4000 IU (100 mcg) per day without supervision.
Key Points
- The tolerable upper intake level (UL) for vitamin D is 4000 IU (100 mcg) per day for most adults and 3000 IU (75 mcg) for older adults.
- Intakes consistently exceeding 4 mg per day (4000 IU) may increase risk of toxicity over time.
- Toxicity symptoms like hypercalcemia may occur with sustained excessive intake over months or years.
- Very high one-time therapeutic doses over 50,000 IU (1250 mcg) require medical monitoring to prevent toxicity.
- Have blood levels checked periodically if supplementing above 2000 IU (50 mcg) daily.
- Toxicity is treatable but long-standing damage may be irreversible, so prevention is key.
Conclusion
While vitamin D is important for health, more is not necessarily better. Excessive intake over time can lead to toxicity, especially without medical oversight. Have your vitamin D blood level tested to determine if you require supplements and in what dose. Do not routinely exceed the UL of 4000 IU (100 mcg) per day without periodic retesting of vitamin D status. Toxicity is unlikely with responsible supplementation within the recommended upper limits.
