Vitamin D is an essential nutrient that plays a critical role in many bodily functions, from strengthening bones to regulating your immune system. According to the National Institutes of Health, an estimated one billion people worldwide have inadequate levels of vitamin D in their blood, which can lead to a host of health problems, including increased risk of infection, osteoporosis, and autoimmune disorders.
Vitamin D and D3 are not the same. Vitamin D has two major forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
Vitamin D3 is more potent than vitamin D2. It is more effective in increasing and maintaining vitamin D levels in the body than vitamin D2.
Vitamin D3 is considered the more biologically active form, as the body can more efficiently convert it into the active hormone form of vitamin D, known as calcitriol. While vitamin D2 is also converted ultimately into calcitriol, vitamin D3 has more efficient absorption, metabolism, bioavailability, and half-life.
Overall, vitamin D3 may provide more beneficial health effects to correct vitamin D deficiency, prevent bone health/fractures, improve immune function, fight COVID-19 infection, and protect from all-cause mortality.
Supplementation provides an attractive strategy to correct low vitamin D status; however, research shows that certain vitamin D forms may be superior. Here, we review the differences between the two forms of vitamin D and discuss their benefits in certain health conditions and diseases.
Is there a difference between vitamin D and vitamin D3?
Yes, there is a difference between vitamin D3 and D. More accurately, vitamin D is the collective term for the group of specific fat-soluble vitamins that include vitamin D2 and vitamin D3.
What is vitamin D?
Vitamin D is a fat-soluble vitamin crucial to maintaining optimal health. It is essential for the absorption of calcium and phosphorus, which are important for bone growth and development, as well as for maintaining strong bones and teeth.
Beyond skeletal functions, vitamin D also provides other health benefits, but depending on the form, it may have more beneficial effects than the other.
Two forms of vitamin D
There are two main forms of vitamin D:
- Vitamin D2 (ergocalciferol)
- Vitamin D3 (cholecalciferol)
Vitamin D3 is considered the more biologically active form, as it is more efficiently converted by the body into the active hormone form of vitamin D, known as calcitriol. Although vitamin D3 is more efficient, vitamin D2 is also converted into calcitriol.
How the body metabolizes vitamin D
Although the two vitamin D forms — D2 and D3 — have only slightly different chemical structures, they have specific differences in their metabolism and properties.
How vitamin D is synthesized in the body
Vitamin D is naturally synthesized in the body when the skin is exposed to sunlight, but it can also be obtained through certain foods and supplements.
Specifically, when our skin is exposed to sunlight, a compound called cholecalciferol (vitamin D3) is produced. This is then transported to the liver, which converts it into 25-hydroxyvitamin D3. From there, it is further processed in the kidney to form the active hormone form of vitamin D, known as 1,25-dihydrovitamin D3 (calcitriol), the final, most active form of vitamin D.
Meanwhile, when vitamin D2 is taken, it is also transported into the liver and follows the same process.
Differences in absorption and metabolism in the body
Vitamin D2 and vitamin D3 differ in their absorption and metabolism in the body, which can impact their effectiveness in maintaining optimal vitamin D levels.
Here are some key differences in terms of absorption, metabolism, bioavailability, and half-life of vitamin D2 and D3:
|Vitamin D2||Vitamin D3|
|Absorption||Less efficient||More efficient|
|Metabolism||Vitamin D2 metabolized in liver to 25-hydroxyvitamin D (25(OH)D), the primary circulating form of vitamin D.||Vitamin D2 metabolized in liver to 25-hydroxyvitamin D (25(OH)D), the primary circulating form of vitamin D.|
More efficiently metabolized than vitamin D2, resulting in higher levels of 25(OH)D in the blood.
|Bioavailability||Less bioavailable||More bioavailable|
|Half-life||Shorter half-life; about 24–48 hours||Longer half-life; about 2–3 weeks|
What is the best form of vitamin D to take?
A large body of data links vitamin D deficiency to the development of acute and chronic conditions, implicating that supplementation may ameliorate such pathologies.
So, which form of vitamin D is more advantageous? We summarize the research findings assessing vitamin D forms and their impact on several diseases or health conditions.
Vitamin D deficiency
Experimental and clinical studies support vitamin D2 and D3 forms for raising vitamin D levels. However, it is now established that vitamin D3 effectively increases blood levels longer than vitamin D2.
In fact, a report concludes that vitamin D3 has approximately 87% higher potency in increasing and maintaining vitamin D levels by 2 to 3 folds compared to vitamin D2.
While some doctors may prescribe vitamin D2 more often than D3, the reason is higher dosages found in vitamin D2 formulations in the market than in vitamin D3. Additionally, vitamin D2 is more readily available in groceries or pharmacies because vitamin D2 is cheaper to produce.
Bone health and fractures
According to research, vitamin D2 and D3 have fairly equal beneficial effects on bone health and bone mineral density, even though vitamin D3 is more effective at raising and maintaining vitamin D blood levels.
Additionally, vitamin D3 may also effectively reduce the risk of falls and fractures, a major issue in the elderly. More recent data indicates that both vitamin D2 and D3 alone could not reduce fracture rate; however, if combined with calcium, these supplements, especially vitamin D3, significantly reduce fracture rates.
Chronic Kidney Disease (CKD)
Patients with CKD have prevalent vitamin D deficiency. However, supplementation is tricky, and correcting vitamin D status in CKD patients requires stricter guidelines that may depend on patient characteristics and disease stage.
When vitamin D2 and D3 supplementation is compared in hemodialysis patients, results show that vitamin D3 is more effective in improving the patients’ vitamin D status.
However, more recent data warrants caution in choosing vitamin D3 form for supplementation.
In 2021, a systematic review of 22 clinical trials testing vitamin D forms in CKD patients stated the effect of its supplementation is inconclusive. The study showed that vitamin D3 analogs (calcifediol and calcitriol) even have varying effects on markers of CKD severity: while calcifediol suppresses PTH, calcitriol may increase FGF23.
When kidney function in CKD patients progressively declines, circulating levels of parathyroid hormone (PTH) and Fibroblast Growth Factor 23 (FGF23) increase and are associated with more severe disease stages.
Additionally, certain groups of people with CKD may also have resistance to vitamin D3, which is associated with kidney disease progression. Hence, CKD patients must always check with their doctors before taking any vitamins, including vitamin D supplements.
Vitamin D deficiency has long been associated with reduced immunity. Vitamin D supplementation may bolster immune defenses against many infections.
Meanwhile, UK scientists recently investigated the effects of Vitamin D2 and D3 on the human immune system and found unequal results.
Regarding IFN activity (a cellular pathway critical in effective response to bacterial and viral infections), only vitamin D3 has a boosting effect. Since reduced IFN activity predisposes people to infection, their findings indicate that vitamin D3 provides a superior boost to immune system processes.
Surprisingly, the researchers also observed some people supplementing with vitamin D2 had lower blood levels than the placebo group. However, since this clinical trial has some limitations, a broader examination of a larger population and a longer time frame is needed.
A 2019 publication by JAMA Cardiology that meta-analyzed 21 clinical trials with over 83,000 individuals concluded that vitamin D (whether ergocalciferol or cholecalciferol) supplementation does not provide cardiovascular protection or beneficial effects related to major cardiovascular events, individual CVD endpoints (stroke, myocardial infarction, CVD mortality) as well as all-cause mortality.
However, later in the same year, another group of scientists published a literature review by the Journal of Clinical Endocrinology & Metabolism. It argued that although current data do not support vitamin D’s benefits for cardiovascular protection, the evidence is still inconclusive, which warrants more comprehensive investigations and rigorous study designs.
Recently, researchers from Johns Hopkins University published the effects of vitamin D supplementation against COVID-19. Data shows that vitamin D2 and D3 supplementation decreased COVID-19 infection probability by 20% and 28%, respectively.
While both forms significantly reduce the risk of COVID-19 infection, further analysis shows that vitamin D3 is associated with a 33% lower risk of SARS-CoV-2 infection and 30-day mortality following infection. But vitamin D2 does not seem to have this positive effect.
Other findings also indicate the higher severity of COVID-19 in patients with vitamin D deficiency.
In 2014, a meta-analysis of 73 cohort studies with over 849,000 participants indicated vitamin D3 supplementation significantly lowers mortality rates in older adults due to cardiovascular disease, cancer, and other causes.
On the other hand, a 2019 meta-analysis of 50 clinical trials with over 74,000 participants suggests vitamin D supplementation alone does not reduce all-cause mortality. Their analysis also showed a 15% reduction in cancer mortality in vitamin D3 supplementation, but not in vitamin D2.
How much vitamin D should I take a day?
The recommended daily vitamin D intake depends on various factors, including age, sex, and overall health. Amounts may also vary depending on whether you get vitamin D from sunlight, food, or supplements.
According to the National Institutes of Health-Office of Dietary Supplements, the recommended vitamin D IU (international units) dosages per day based on age groups are as follows:
|Birth: 0–12 months old||10 mcg (400 IU)||10 mcg (400 IU)||-||-|
|Children: 1–13 y/o||15 mcg (600 IU)||15 mcg (600 IU)||-||-|
|Teens: 14–18 y/o||15 mcg (600 IU)||15 mcg (600 IU)||15 mcg (600 IU)||15 mcg (600 IU)|
|Adults: 19–50 y/o||15 mcg (600 IU)||15 mcg (600 IU)||15 mcg (600 IU)||15 mcg (600 IU)|
|Older adults: 51–70 y/o||15 mcg (600 IU)||15 mcg (600 IU)||-||-|
|Elderly: >70 y/o||20 mcg (800 IU)||20 mcg (800 IU)||-||-|
However, when it comes to vitamin D2 and D3 specifically, there is no clear consensus on how much of each form you should take. As previously mentioned, both vitamin D forms, effectively increase vitamin D blood levels, but vitamin D3 is more effective.
Where can I get vitamin D?
Since vitamin D deficiency has been linked to various health problems, ensuring you get enough vitamin D through a balanced diet and appropriate sun exposure is important.
Vitamin D2 is primarily found in plant sources, while vitamin D3 is synthesized in the skin when exposed to sunlight and is also found in animal products. You can improve your vitamin D status by taking specific vitamin D-rich sources.
Vitamin D2 sources
- Mushrooms (especially those exposed to UV light)
- Fortified foods such as milk, orange juice, and cereal
- Supplements (in the form of ergocalciferol)
Vitamin D3 sources
- Fatty fish such as salmon, tuna, and mackerel
- Egg yolks
- Beef liver
- Fortified foods such as milk, orange juice, and cereal
- Supplements (in the form of cholecalciferol)
Does vitamin D3 improve skin?
Yes, vitamin D3 can improve skin health by regulating skin cell growth, promoting skin health, and preventing certain skin conditions. Specifically, it has anti-inflammatory effects that can benefit people with inflammatory skin conditions such as eczema and psoriasis.
What happens if you take vitamin D3 every day?
Taking vitamin D3 every day in appropriate doses can help maintain healthy bones and teeth, improve immune function, and prevent vitamin D deficiency. However, excessive intake can lead to toxicity, which can cause symptoms such as nausea, vomiting, weakness, and kidney damage.
Which vitamin D is needed for the skin?
While both vitamin D2 and D3 can play a role in maintaining healthy skin, vitamin D3 may be more effective. Adequate levels of vitamin D3 can help regulate skin health and prevent certain skin conditions.
- The Journal of Clinical Endocrinology & Metabolism. Vitamin D3 Is More Potent Than Vitamin D2 in Humans.
- Medicine (Baltimore). Vitamin D supplement on prevention of fall and fracture.
- Therapeutics and Clinical Risk Management. The use of calcium and vitamin D in the management of osteoporosis.
- Journal of Nephrology. Vitamin D2 versus vitamin D3 supplementation in hemodialysis patients: a comparative pilot study.
- Calcified Tissue International. Vitamin D Supplementation for Patients with Chronic Kidney Disease: A Systematic Review and Meta-analyses of Trials Investigating the Response to Supplementation and an Overview of Guidelines.
Show all references
- Frontiers in Immunology. Vitamins D2 and D3 Have Overlapping But Different Effects on the Human Immune System Revealed Through Analysis of the Blood Transcriptome.
- JAMA Cardiology. Vitamin D Supplementation and Cardiovascular Disease Risks in More Than 83 000 Individuals in 21 Randomized Clinical Trials: A Meta-analysis.
- The Journal of Clinical Endocrinology & Metabolism. Vitamin D and Atherosclerotic Cardiovascular Disease.
- Nature Scientific Reports. Association between vitamin D supplementation and COVID-19 infection and mortality.
- The BMJ. Vitamin D and risk of cause specific death: systematic review and meta-analysis of observational cohort and randomised intervention studies.
- National Institutes of Health-Office of Dietary Supplements. Vitamin D Fact Sheet for Health Professionals.