Pharmacology is the branch of medicine that is focused on the use and study of drugs and their actions. This page discusses vitamin D in pharmacology, its different forms and the use of vitamin D analogues.
This is an advanced topic, primarily focused to educate health professionals, or to answer any questions a person might have on some form of vitamin D their doctor prescribed
When we say vitamin D, we are talking about vitamin D nutritionally, in the form of cholecalciferol (vitamin D₃) or ergocalciferol (vitamin D₂). Cholecalciferol is made in the skin in response to UVB radiation. Ergocalciferol is produced in plants and fungus, also in response to UVB radiation.
Cholecalciferol and ergocalciferol can both be found in the form of a supplement. In the United States, “over the counter” vitamin D is usually cholecalciferol, but this is not always the case. Cholecalciferol is produced by irradiating sheep wool. Cholecalciferol is also in cod liver oil products. Ergocalciferol supplements are produced much more complicatedly, often involving irradiating sugars and yeasts.
Vitamin D is scarcely found in food. Fatty fish have small quantities of cholecalciferol, while irradiated mushrooms have small quantities of ergocalciferol.
In the United States and Canada, the Institute of Medicine currently recommends the following daily intakes:
|Infants, 0-12 months||400 IU|
|Children, pregnant women and adults, 1-70 years||600 IU|
|Seniors, >70 years||800 IU|
The European Union recommends the following daily intake:
|All ages/groups||200 IU (5μg)|
Sometimes you’ll hear scientists refer to “physiologic doses of vitamin D.” A physiologic dose of vitamin D is the dose required to maintain vitamin D blood levels [25(OH)D] in the range that ancestral humans maintained. Since ancestral humans received much more sun exposure than modern day humans get, researchers and doctors will study or prescribe physiologic doses of vitamin D, to make up for the absence of sunlight.
So what is a physiologic dose? This is a dose between 3,000-5,000 IU/day, which will help you achieve the same vitamin D levels of someone who gets lots of year-round full-body sun exposure around the equator.
Some researchers, as well as the Vitamin D Council, believe that physiologic doses of vitamin D should be the public recommendation until research guides us otherwise. This is why the Vitamin D Council recommends 5,000 IU/day, to make up for the sunshine most modern day humans don’t get.
A “pharmacologic dose of vitamin D” is a term referring to any dose greater than a daily physiologic dose. These are also sometimes called ‘mega doses,’ ‘loading doses’ or ‘Stoss doses.’ Doctors will sometimes use pharmacologic doses to quickly raise vitamin D blood levels. A common practice is to prescribe a pharmacologic dose of vitamin D (50,000 IU once per week) when a patient tests low in vitamin D. Researchers will also sometimes use pharmacologic doses in their studies, also to quickly raise vitamin D blood levels.
In general, the Vitamin D Council believes that daily physiologic doses are preferable to pharmacologic doses, though every individual has different needs. If a patient is low in vitamin D, sometimes it is prudent to prescribe both a pharmacologic and physiologic dose. Or in simpler terms, a mega dose for the short term, and a daily maintenance dose for the long term.
A few studies have shown that cholecalciferol (vitamin D₃) is better than ergocalciferol (vitamin D₂) at increasing vitamin D levels and better for various health outcomes and mortality risk. Also, since the body produces cholecalciferol rather than ergocalciferol, it is commonly thought that cholecalciferol is better for people than ergocalciferol.
There are no studies that show whether vitamin D in tablet, gel, capsule, drop or sublingual form is preferable. There are a few vitamin D cream products on the market. At this time, there are no studies that examine how well, if at all, vitamin D is absorbed through applying creams to the skin.
Vitamin D supplements are widely available “over the counter” in the United States. These supplements are usually vitamin D₃, but it’s important to check the label to make sure. Vitamin D supplements come in a variety of IUs per pill, some of the most common sizes being 400 IU, 1,000 IU, 2,000 IU and 5,000 IU, though products vary.
Vitamin D is also usually found in multi-vitamins, found in amounts of 400 to 1,000 IU, though sometimes more. Vitamin D is also sometimes coupled with calcium and promoted for bone health.
Unless a doctor takes extra care in prescribing their patient vitamin D, patients are prescribed a product called Drisdol. Drisdol is ergocalciferol (vitamin D₂) in 50,000 IU pills, usually prescribed to take once or twice weekly, fortnightly or monthly.
The Vitamin D Council generally recommends against this because vitamin D₃ is preferable to vitamin D₂. It should also be considered, that rather than just take a weekly dose of vitamin D in the short run, a long term strategy should be setup to get daily vitamin D in the long run.
Most people can take vitamin D supplements with no problems. However, care is needed in a few situations. These situations include:
A vitamin D metabolite is a chemical in the body that the body produces when you take vitamin D. When vitamin D is taken, the liver turns vitamin D into 25(OH)D. Then the kidney and many other tissues in the body take this 25(OH)D and turn it into 1,25(OH)₂D. Since these are the forms the body wants and uses, sometimes doctors prescribe these forms if you can’t produce them yourself when you take vitamin D.
However, in the United States, 25(OH)D is not available over the counter or by prescription. It has been available in the past. It is not known if it will be available in the future.
1,25(OH)₂D (activated vitamin D) is available by prescription, sold under the trade names Rocaltrol, Calcijex and Decostriol. The use of 1,25(OH)₂D is not to treat vitamin D deficiency, but rather treat hypocalcemia and bone disease in people with abnormal conditions like hypoparathyroidism, kidney disease, osteomalacia, rickets and others. 1,25(OH)₂D is prescribed in these instances because the person has difficulty producing 1,25(OH)₂D in their kidney, or maybe they need extra 1,25(OH)₂D to compensate for lack of parathyroid hormone and more. Sometimes doctors recommend those with kidney diseases to take both plain vitamin D and 1,25(OH)₂D.
Vitamin D analogs are drugs chemically and physiologically similar to vitamin D or its metabolites. They are developed by researchers for specific purposes.
Most analogs on the market are used to treat people with kidney disease, those at risk of low blood calcium, and those at risk of bone diseases and other rare medical conditions. There are also analog creams that have also been developed to treat skin disorders like psoriasis.
Here are some analogs currently available on the market: