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Prescription pad and Rx pill bottle: Vitamin D side effects and how to avoid them
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Vitamin D side effects and how to avoid them

Vitamin D side effects can include vitamin D toxicity from taking too high of a dosage over a sustained period
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By | Updated on Jun. 30, 2023 Medically reviewed by Karen Berger, Pharm.D.

Common vitamin D side effects | Serious side effects | Vitamin D toxicity | Side effects timeline | Contraindications | Warnings | Interactions | How to avoid side effects | How to treat side effects

Vitamin D is an essential nutrient responsible for calcium absorption and maintaining adequate levels of calcium in the body. It’s important for bone health, bone strength, nerve functioning, muscle strength, and the immune system. Vitamin D is normally produced by the skin when it is exposed to the sun’s ultraviolet-B radiation (UVB) but it also can be found in certain vitamin supplements and some foods. 

Having low vitamin D in the body is both a serious and common problem. Many children have a vitamin D deficiency, and the problem is common in adults who are overweight, pregnant, use sunblock, or otherwise don’t get enough sun exposure. Chronic vitamin D deficiency can lead to weak bones, bone fractures, and rickets (in children), and it is the major cause of generalized bone pain and muscle pain complaints. People take vitamin D supplements to avoid or correct vitamin D deficiencies. These supplements—available as synthetic vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol)—come in both over-the-counter and prescription dose strengths. Higher-dose prescription vitamin D is usually given to people with vitamin D deficiency, low parathyroid function (hypoparathyroidism, a condition that causes low blood calcium), and bone softening (osteomalacia). Side effects from both over-the-counter and vitamin D supplements are generally only a problem if too much vitamin D is taken over a long period.

Common side effects of vitamin D

Common side effects of vitamin D supplements may include: 

  • Nausea and vomiting
  • Headache
  • Irritability 
  • Tiredness
  • Excess thirst
  • Frequent urination
  • Appetite and weight loss

Some adverse effects are due to taking too much vitamin D. In those cases, vitamin D toxicity (hypervitaminosis D) can cause several problems:

  • High levels of calcium in the blood (hypercalcemia)
  • Vomiting
  • Nausea
  • Headache
  • Irritability
  • Loss of appetite
  • Weight loss
  • Weakness
  • Constipation
  • Kidney dysfunction including:
    • Excessive or frequent urination
    • Thirst
    • High blood pressure
    • High calcium in the urine
    • Kidney damage (which could cause death)
  • Acidic blood (acidosis)
  • Anemia
  • Calcium deposits (calcification) in the blood vessels, heart, lungs, kidneys, and other soft tissues
  • Osteoporosis (a condition where the bones become weak and brittle)
  • Slow growth in children

Serious side effects of vitamin D

Many of the common side effects of vitamin D overdose are very serious and related to how long calcium remains at high levels in the body. These include:

  • Kidney dysfunction
  • Kidney damage
  • Kidney failure
  • Acidosis
  • Anemia
  • Calcification of soft tissues, blood vessels, and organs
  • Osteoporosis
  • Slow growth and dwarfism (in children)

Vitamin D toxicity (hypervitaminosis D)

Overdosing on vitamin D for months or years can cause a rare but serious condition called hypervitaminosis D. High vitamin D levels in the blood raises calcium levels to dangerous levels and also leeches calcium from the bones, producing the side effects listed above. Overdosing on vitamin D only happens when people take too many vitamin D supplements or are prescribed high doses of vitamin D. However, people prescribed high-dose vitamin D will have regular blood tests to measure vitamin D and calcium levels to avoid vitamin D toxicity. About 4,000 people a year in the United States are diagnosed with vitamin D toxicity. In some extremely rare cases, people can have hypersensitivity to vitamin D. In those cases, normal vitamin D intake could be an overdose and cause high blood calcium. In these cases, vitamin D intake will be restricted. 

How soon do vitamin D side effects start?

Vitamin D side effects usually take months or years of overdosing to become a problem, though some of the milder side effects such as vomiting or excessive urination may be some of the first symptoms to appear.

How long do vitamin D side effects last?

The side effects of vitamin D toxicity can last for two months or more after vitamin D and calcium intake have been restricted. In terms of treatment for vitamin D toxicity, some patients may need to limit dietary calcium and consume excess fluids. More severe cases require aggressive treatment with IV saline, diuretics (to help remove calcium from the body), and corticosteroids. Some patients need dialysis and/or other medications. 

What are the long-term side effects of vitamin D?

Many side effects of vitamin D supplements are long-term side effects due to taking too much vitamin D. What constitutes an overdose has not been determined, but the Institute of Medicine has set the upper safe limit at 4,000 International Units daily. Overdosing could take years before becoming a problem (if problems develop at all). There is a small window between where vitamin D is therapeutic and where it can be toxic. Prescription doses can be as high as 500,000 IU a day in certain cases, so healthcare providers will monitor blood levels of both vitamin D and calcium at least every two weeks in these patients. They will modify treatment if high blood calcium becomes a problem. Many patients only need to take a small daily dose or a larger weekly dose (for example, 50,000 IU per week) and will be monitored occasionally, but not as frequently as those who take higher doses. Your healthcare provider will tell you how much vitamin D to take and how often you will need blood work.

Vitamin D contraindications

Vitamin D supplements should never be taken by people with:

  • Vitamin D toxicity
  • High blood calcium
  • Allergies to any of the ingredients in the supplement
  • Renal osteodystrophy (a complication of kidney disease that affects the bones and soft tissues)

Pregnancy

High-dose vitamin D is not recommended in pregnant women, although taking the suggested daily allowance is not prohibited. Vitamin D toxicity can affect a fetus and cause heart defects and developmental disabilities.

Breastfeeding

High-dose vitamin D is not recommended in women who are breastfeeding. The infant is at risk of high blood calcium due to ingesting high vitamin D doses through breast milk. If you are breastfeeding, consult your healthcare provider before taking vitamin D.

Children

Children who need vitamin D supplementation will be prescribed or recommended an individualized dose and carefully monitored with regular blood tests to prevent vitamin D toxicity. 

Older adults

High-dose vitamin D is not well-studied in older patients. People aged 65 and older are less efficient at absorbing vitamin D from foods or supplements. If vitamin D supplementation is a concern, blood tests can help identify a vitamin D deficiency. A healthcare provider can then suggest a supplementation regimen. For prescription vitamin D, a healthcare provider will start at the lowest possible dose and regularly perform blood tests to monitor vitamin D and calcium levels. 

Vitamin D warnings

As a supplement widely available in over-the-counter vitamins and multivitamins, vitamin D has only a few warnings and cautions. The most important warning: Don’t overdo it. Either follow the suggested guidelines or take the prescribed dose, but no more than that.

Cautions

A few medical conditions may cause problems when taking vitamin D, particularly in high doses. These include:

  • Kidney stones. Raising vitamin D levels in the body can increase calcium levels in urine, which can contribute to the growth of some types of kidney stones.
  • Kidney dysfunction. People with kidney disease are more likely to experience high calcium when taking vitamin D. Higher calcium in the blood makes the kidneys work harder to filter blood, putting an added strain on the kidneys. 
  • High phosphate levels. Vitamin D regulates the absorption of phosphate and calcium through the intestines. Higher levels of vitamin D will cause the digestive system to absorb more phosphate, worsening pre-existing high phosphate levels.
  • Malabsorption syndrome. Some medical conditions such as Crohn’s disease, cystic fibrosis, liver disease, or gallbladder problems diminish the digestive system’s ability to absorb fat-soluble vitamins like vitamin D. In those cases, higher amounts of vitamin D may need to be given.

Abuse and dependence

Vitamin D has no risk of drug abuse or drug dependence. 

Overdose

A single overdose of vitamin D will not cause major problems, though there may be digestive system issues. If too much vitamin D is taken at once, call a poison control center for advice. If a child takes too much vitamin D, call poison control. Because vitamin D toxicity can be very serious, take the child to the emergency room. 

Daily and chronic overdosing, however, can result in vitamin D toxicity, a serious medical condition characterized by the side effects listed above. If any cluster of these symptoms is noticed, immediate medical help is needed.

Vitamin D interactions

Vitamin D supplements have few drug interactions. Most involve drugs that reduce the effectiveness of taking the supplement. 

  • Vitamin D. To avoid vitamin D toxicity, don’t combine vitamin D supplements with other vitamin D supplements unless the total daily dose is within guidelines.
  • Calcium. To avoid high calcium, be prudent in taking calcium supplements or medicines containing calcium such as some antacids.
  • Mineral oil. Mineral oil can interfere with the body’s absorption of vitamin D through the intestines.
  • Bile acid resins. Used to treat high cholesterol, bile acid resins interfere with the digestive system’s ability to absorb fat-soluble vitamins like vitamin D.
  • Thiazide diuretics. Combining vitamin D2 with thiazide diuretics such as hydrochlorothiazide can cause high calcium in people with low parathyroid function.

How to avoid vitamin D side effects

Avoiding vitamin D side effects involves a simple rule: don’t take too much. Here’s how to do it.

1. Know the right amount of vitamin D to take each day

Don’t guess. Look this up. There are two major guidelines for vitamin D intake. The Endocrine Society recommends 1,500 to 2,000 IU of vitamin D daily for adults. Infants less than one-year-old should get 400 to 1,000 IU daily, and children and adolescents should get 600 to 1,000 IU each day. The Institute of Medicine suggests lower daily doses: 400 IU daily for children and adults, and up to 800 IU daily for adults 71 years and older. Both recommendations are well below the maximum safe daily dose of 4,000 IU. Either way, your best bet is to ask your healthcare provider or your child’s pediatrician for a dosage recommendation based on lab results and/or guidelines. 

2. Know how much vitamin D is being taken each day

Many foods are fortified with vitamin D including milk, breakfast cereals, bread, and children’s foods. It may be possible that there’s enough vitamin D already in the diet, particularly for kids with a fondness for these foods. Check all the foods being eaten each day. Check any dietary supplements, like fish oil, for vitamin D. Add up the daily vitamin D intake. This will determine how many vitamin D supplements need to be taken. 

3. Know how much calcium to take each day

Vitamin D toxicity is also related to calcium intake. The IOM recommends a daily calcium dose of:

  • Children ages 1 to 3 years old: 500 mg per day
  • Children ages 4 to 8 years old: 800 mg per day
  • Children/teenagers ages 9 to 18 years old: 1,300 mg per day
  • Women 19 to 50 years old: 800 mg per day
  • Women > 50 years old: 1,000 mg per day
  • Men up to 71 years old: 800 mg per day
  • Men 71 years and older: 1,000 mg per day

Again, there may be enough calcium in the diet, so take a look at all the other foods, dietary supplements, and calcium-containing drugs that are being taken to decide how much calcium needs to be added in the form of supplements.

4. Tell the prescriber about all medical conditions

If vitamin D is being prescribed by a healthcare professional, make sure the prescriber knows about all medical conditions and any drugs or supplements being taken. The most important are:

  • Kidney disease
  • Kidney stones
  • High phosphate in the blood
  • Crohn’s disease
  • Gallbladder disease
  • Liver disease
  • Cystic fibrosis
  • Pregnancy or pregnancy plans
  • Breastfeeding or breastfeeding plans

5. Keep all follow-up appointments

If prescribed high doses of vitamin D, keep all follow-up and lab appointments. Many of the doses prescribed are enough to produce vitamin D toxicity, so regular blood tests are required to spot high levels of vitamin D or calcium before kidneys or tissues are damaged.

How to treat side effects of vitamin D

If any cluster of symptoms associated with vitamin D toxicity is noticed, stop using vitamin D and calcium supplements. Get immediate medical attention.

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