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When would I need a prescription for vitamin D?

Nicole Roder writer headshot By | January 24, 2020
Medically reviewed by Kristi C. Torres, Pharm.D.

It’s that time of year when much of the United States experiences dreary weather and less time in the sun. When it comes to your health, many people tend to associate winter weather with the flu or the common cold. But there is an important nutrient that many of us are missing out on, especially in the wintertime, and it plays a big role in your bone health: vitamin D.

What is vitamin D?

“Vitamin D is a fat soluble vitamin that is needed for calcium to be absorbed into your bones,” says Dr. Inna Lukyanovsky, Pharm.D., functional medicine practitioner and the author of The Crohn’s and Colitis Fix.

Chirag Shah, MD, co-founder of Push Health, elaborates: “Vitamin D is a type of molecule known as a secosteroid. Vitamin D is biologically active in the body and helps increase the absorption of electrolytes, including calcium and magnesium, from the gastrointestinal tract.”  

In other words, your bones can’t absorb calcium without vitamin D. That’s why most cow’s milk sold in U.S. grocery stores is fortified with vitamin D. No matter how much of that great calcium you get from foods, your bones will be soft and brittle unless you also take in enough vitamin D to process it. 

Why would a doctor prescribe vitamin D?

Vitamin D prescriptions might be on the rise. One study found that testing for vitamin D deficiencies and subsequent prescriptions of the fat soluble vitamin increased more than sevenfold between 2008 and 2013. Why the huge increase? Researchers believe that it was due to a global increase in awareness of patients who are vitamin D deficient, rather than an actual increase in need. 

So why would a doctor prescribe vitamin D supplementation? There are several reasons, but it starts with the vitamin’s accessibility. 

Where do we get vitamin D?

“Vitamin D is obtained from few food sources in any significant quantity (liver, wild caught salmon, and minimal amounts in fortified milk),” says Arielle Levitan, MD, co-founder of Vous Vitamin and author of The Vitamin Solution. “It can be obtained from exposure to the sun.” 

But a lot of people don’t get enough vitamin D from food or sun exposure. If that’s the case, they might need to take a vitamin D supplement. Sometimes people can get what they need from an over-the-counter (OTC) supplement, but many people need a prescription from their doctor. You can find generic vitamin D supplements in pharmacies and drugstores as well as brand-name supplements such as Drisdol and Calciferol.

Medical conditions that require vitamin D prescription

“Vitamin D is commonly prescribed for hypoparathyroidism [a condition that causes calcium deficiency, muscle cramps and spasms, weakness, and fatigue],” says Dr. Lukyanovsky. “Doctors might also prescribe it for osteomalacia, a condition where there’s a depletion of calcium from the bone.” 

There are other medical conditions that might necessitate a vitamin D prescription. For example, hypocalcemia is a condition that is marked by insufficient calcium in the blood. Doctors treat it with specific types of vitamin D called alfacalcidol, calcifediol, calcitriol, and dihydrotachysterol. Alfacalcidol, calcifediol, and calcitriol are also prescribed for the treatment of certain types of bone disease that are common in kidney dialysis patients.

Vitamin D deficiency

All of our medical experts tell us that one of the most common reasons for prescribing vitamin D is a deficiency of it. If a patient is experiencing symptoms of vitamin D deficiency, such as bone loss, hair loss, bone and back pain, and difficulty healing from wounds, their healthcare provider will most likely order a lab test to confirm vitamin D deficiency. 

Blood levels of 20 nanograms/milliliter to 50 ng/mL of vitamin D is considered within normal range for healthy people. If the lab results show a low vitamin D level that’s below 12 ng/mL, that indicates a vitamin D deficiency.

Vitamin D deficiency is very serious. If the amount of vitamin D in the blood is too low, it can cause a condition called Rickets in children. Rickets is a rare disease. It causes children’s bones to become soft and bend, sometimes forming “bow legs.” African American children are at highest risk of getting rickets. 

As mentioned above, adults can also suffer medical consequences from not enough vitamin D, including the bone disease osteomalacia.

Some doctors think vitamin D could be connected to more medical conditions, like high blood pressure, diabetes, cancer, and multiple sclerosis. Researchers are studying potential links, but more research is needed before we can truly understand the relationship between vitamin D and these conditions. 

Populations at special risk for vitamin D deficiency

There are some people who are particularly vulnerable to vitamin D deficiency, and they might need to take over-the-counter or prescription supplements even without symptoms. 

  • Breastfed infants: Vitamin D is not present in significant amounts in human breast milk, and the American Academy of Pediatrics recommends against exposing infants to direct sunlight without sunscreen. This means these babies are at risk of a vitamin D deficiency, and possibly Rickets. They should take a dietary supplement of 400 international units (IU) of vitamin D per day. 
  • Older adults: In old age, the skin is less able to absorb vitamin D from the sun. 
  • Pregnant women: During pregnancy, some women are at increased risk of vitamin D deficiency. Taking a daily vitamin D supplement of 4,000 IU during pregnancy might reduce the risk of gestational diabetes and early labor.
  • People who are obese: Their body fat can bind to some vitamin D and prevent it from getting to the blood.
  • People who have had gastric bypass surgery.
  • People with osteoporosis, kidney disease, or liver disease.
  • People with dark skin: The higher amounts of skin pigmentation make it more difficult to produce vitamin D from sunlight. 
  • People with Crohn’s disease or celiac disease: These disorders cause the body to have difficulty handling fat, which is needed in order to absorb this fat soluble vitamin.
  • People with hyperparathyroidism: This means that their bodies have too much of the parathyroid hormone, which controls the body’s calcium level.
  • People who take certain medicines: Some medications, such as cholestyramine, anti-seizure drugs, glucocorticoids, HIV/AIDS medications, and antifungal drugs, can affect your body’s metabolism of vitamin D. 

Vitamin D2 vs. D3

Did you know that vitamin D actually comes in multiple forms? The two most important forms of vitamin D for your health are D2 and D3

“Vitamin D2 is known as ergocalciferol while vitamin D3 is known as cholecalciferol,” says Dr. Shah. “Vitamin D2 typically originates from plant-based sources while vitamin D3 is generally found in animal sources.”

And we’re not just talking food here. Remember, humans are animals, too. So the vitamin D that your skin absorbs from the sun is the D3 form.

Dr. Levitan says that people who need vitamin D supplements should take D3. This is the most active form of vitamin D in your body, as the liver converts D2 to D3. Though most people can easily metabolize D2 as well. 

What is prescription-strength vitamin D?

We’ve been talking a lot about vitamin D prescriptions. But the truth is, many doctors “prescribe” their patients to take over-the-counter vitamin D supplements. Higher doses of OTC supplements are available in 400 IU, 800 IU, 1000 IU, 2000 IU, 5000 IU, and 10,000 IU tablets and liquid drops. 

Prescription strength vitamin D contains a high dose of 50,000 IU. But our experts say that this dose is not necessary for most people.

“The best way to take vitamin D is via a daily year-round dose through a personalized vitamin regimen,” says Dr. Levitan. “The amount each individual needs varies based on who you are, where you live, ethnicity, medical issues and more. There are ‘mega dose’ prescription products of D3, which can be taken weekly in tablet form. However, these are rarely needed other than in extreme cases and in people with GI absorption issues (I.e., Crohn’s disease). Ultimately most people can maintain a normal vitamin D level with a daily dose between 800 and 2000 IU daily.  This can be taken in tablet, capsule, or drop forms. The best way to get exactly what you need is to take a doctor-created custom regimen to meet your exact vitamin needs.” 

Vitamin D side effects and interactions

According to Dr. Lukyanovsky, the following are potential side effects of vitamin D supplements:

  • Bone pain
  • Muscle weakness
  • Nausea, vomiting, or constipation
  • Extreme thirst
  • Frequent urination
  • Kidney stones
  • Confusion or disorientation
  • Weight loss or poor appetite
  • Fatigue

Dr. Lukyanovsky explains that Vitamin D supplements can also negatively interact with certain medications, so talk to your doctor before taking them if you are also taking any of these drugs.

  • Diabetes medicines
  • Blood pressure medicines
  • Calcium supplements
  • Antacids
  • Corticosteroids, such as prednisone
  • Weight-loss medicines, including Alli (orlistat)
  • Questran, LoCholest, or Prevalite (cholestyramine)
  • Seizure medicines, including phenobarbital and Dilantin (phenytoin)

It’s possible to consume too much vitamin D. If your daily intake of vitamin D far exceeds the recommended dietary allowance (RDA) can lead to vitamin D toxicity, which causes build up of calcium in the blood (hypercalcemia), nausea, and vomiting.  

As with any medications, you should always seek medical advice from your healthcare provider before you take a vitamin D supplement, even if it’s over-the-counter. Not only is it possible for the supplements to interact with other medications you are taking, or affect conditions you might have, but you need to know the right dose of vitamin D for you, too.