What is Vitamin D?

Vitamin D is an important nutrient that helps your body absorb calcium and maintain strong bones.  Your body can make vitamin D when your skin is exposed to sunlight.  Still, many people don't get enough sun exposure, especially during the winter months.  Vitamin D is also found in some foods like fatty fish, eggs, and fortified milk, but it's hard to get enough from diet alone.  [3]

Why Might You Need a Supplement?

If you live in northern areas, have darker skin, are elderly, or spend most of your time indoors, you may not make enough vitamin D naturally.  Your healthcare provider can check your vitamin D level with a blood test to see if you need supplementation.  [3]

Types of Vitamin D Supplements

There are two forms of vitamin D available as supplements:

Vitamin D3 (Cholecalciferol)

• This is the same form of vitamin D your body makes from sunlight.
• Most vitamin D3 comes from lanolin (sheep's wool), making it an animal product.
• Vegan vitamin D3 made from lichen (a type of plant) is also available.
• Studies show vitamin D3 is more effective at raising vitamin D levels in your blood than vitamin D2 [4-6]
• Vitamin D3 stays in your body longer (about 82 days) compared to vitamin D2 (about 33 days) [7]
• Important note for people with higher body weight: If your body mass index (BMI) is greater than 25, the difference in effectiveness between vitamin D2 and vitamin D3 becomes much smaller and may not be statistically significant [3]

Vitamin D2 (Ergocalciferol)

• This form comes from plants (fungi and yeast)
• It is suitable for vegans and vegetarians.
• It works well to raise vitamin D levels, though you may need a higher dose compared to vitamin D3 [2][4]
• When you take vitamin D2, it can lower the levels of vitamin D3 that your body makes naturally [5][8]
• Important note for people with higher body weight: If your BMI is greater than 25, vitamin D2 may work nearly as well as vitamin D3 for raising your vitamin D levels [3]

Important Information About Manufacturing

Vitamin D3 supplements from lanolin are made using a process that involves certain chemicals (like n-hexane, EDTA, and ionic liquids) to extract and purify the vitamin D. These chemicals are supposed to be completely removed before the final product reaches you.  There are currently no studies proving these chemicals are completely safe for long-term use, but there are also no studies showing they cause harm.  No cases of illness from these extraction chemicals have been reported in medical literature.[3][9-10]

Vegan vitamin D3 is produced by extracting naturally occurring vitamin D3 from lichen species (such as Cladina arbuscula), typically using olive oil-based maceration or other solvent extraction methods.  Unlike animal-derived vitamin D3 from lanolin—which requires extraction with chemicals like n-hexane, EDTA, and ionic liquids—extraction from lichen uses food-grade solvents like olive oil, avoiding the chemicals used in lanolin-based production.

Vitamin D2 is produced by a different process that uses ultraviolet light on plant materials and does not involve extraction chemicals.  [2]

Quality Differences Between Prescription and Over-the-Counter Vitamin D

This is very important to know: not all vitamin D supplements contain the amount listed on the label.

• Prescription vitamin D formulations (which require a doctor's prescription) are more strictly regulated and contain 90-97% of the labeled amount of vitamin D. [1-2]
• Over-the-counter dietary supplements (which you can buy without a prescription) are less strictly regulated and may contain anywhere from 8% to 201% of the labeled amount of vitamin D. [1-2]
• In one study, 8 out of 11 over-the-counter vitamin D supplements failed to meet even the less-stringent standard for dietary supplements (80-150% of the labeled claim). [2]

What to Do About Insurance Coverage

Most insurance companies do not cover prescription vitamin D, even though prescription formulations are more reliable in their vitamin D content.  Here are your options: [3]

1. Ask your healthcare provider about reliable over-the-counter brands.  While we cannot recommend specific brand names in this handout, your healthcare provider can suggest brands that have been independently tested for quality and accuracy.
2. Look for products that have been tested by independent organizations such as the United States Pharmacopeia (USP), NSF International, or ConsumerLab.  These organizations test supplements to verify that they contain what the label claims.
3. Consider prescription vitamin D if cost is not a barrier.  Even though insurance may not cover it, prescription vitamin D formulations are more reliable.  They may be worth the out-of-pocket cost for peace of mind about quality.
4. Have your vitamin D levels monitored more frequently if you choose over-the-counter supplements to ensure you're getting the right amount.

How Much Should You Take?

• Most adults need 800-1,000 IU (International Units) per day to maintain healthy vitamin D levels. [2-3]
• Up to 4,000 IU per day is considered safe for adults. [1]
• If your vitamin D level is very low, your healthcare provider may prescribe higher doses temporarily.
• Because vitamin D2 is less potent, you may need up to three times as much vitamin D2 to achieve the same effect as vitamin D3. [2]
• If you have a higher body weight (BMI >25 kg/m²), you may need 1.5 to 3 times more vitamin D than someone with normal body weight to achieve the same vitamin D levels. [2]

Safety and Side Effects

Both forms of vitamin D are safe when taken at recommended doses.  Very high doses (over 10,000 IU per day) can cause problems, including:

• High calcium levels in the blood
• Kidney stones (affects about 2-4% of people taking vitamin D with calcium) [11]
• Nausea or stomach problems
• Weakness [1]

Cost and Availability

Both vitamin D2 and vitamin D3 are widely available without a prescription and cost about $10-50 per year.  Vegan vitamin D3 from lichen may be slightly harder to find, but it is becoming more available.  [3]

Making Your Choice

You may prefer vitamin D3 if:

• You want the most effective form for raising vitamin D levels (especially if you have normal body weight)
• You don't have dietary restrictions against animal products
• You want to take a lower dose
• You can find a reliable, quality-tested brand

You may prefer vitamin D2 if:

• You follow a vegan diet and cannot find lichen-based vitamin D3
• You prefer to avoid products made with extraction chemicals
• You have a BMI greater than 25 (the difference in effectiveness is smaller)
• You are willing to take higher doses and have more frequent monitoring

You may prefer vegan vitamin D3 (from lichen) if:

• You follow a vegan diet
• You want the effectiveness of vitamin D3
• You can find a quality-tested product in your area

Talk to Your Healthcare Provider

Your healthcare provider can help you decide which form of vitamin D is best for you based on your vitamin D levels, dietary preferences, body weight, and health needs.  She can also:

• Recommend specific over-the-counter brands that have been independently tested for quality
• Monitor your vitamin D levels with blood tests to make sure you're taking the right amount
• Adjust your dose based on your individual response [2-3]

Key Takeaways

Both vitamin D2 and vitamin D3 can effectively treat vitamin D deficiency when taken at appropriate doses with monitoring.  Vitamin D3 is more potent and recommended by most medical guidelines; however, the difference is not statistically significant in people with higher body weight (BMI >25).  Vitamin D2 is a suitable alternative, especially for those with dietary restrictions or concerns about manufacturing processes.  [3-6].  A vegan form of Vitamin 3 is also available.

Because over-the-counter supplements vary widely in their actual vitamin D content (from 8% to 201% of what's on the label), it's important to choose products that have been independently tested for quality by organizations like USP, NSF International, or ConsumerLab.  These certifications help ensure you're getting the amount of vitamin D listed on the label.  [1-2] Prescription vitamin D formulations are more reliable (containing 90-97% of labeled amounts) but are typically not covered by insurance.[1-2]

Work with your healthcare provider to select a high-quality vitamin D supplement that matches your dietary preferences, body weight, and health needs.  Regular monitoring of your vitamin D levels through blood tests will help ensure you're taking the right amount to achieve and maintain healthy vitamin D status.  [4][6-7]

Remember: The most important factor is not which form of vitamin D you choose, but instead that you choose a quality product, take it consistently at an appropriate dose for your body weight, and have your levels monitored to ensure the supplement is working effectively for you.

References

• Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline.
• Demay MB, Pittas AG, Bikle DD, et al. The Journal of Clinical Endocrinology and Metabolism. 2024;109(8):1907-1947. doi:10.1210/clinem/dgae290.
• Comparison of Vitamin D2 and Vitamin D3 Supplementation in Raising Serum 25-Hydroxyvitamin D Status: A Systematic Review and Meta-Analysis.
• Tripkovic L, Lambert H, Hart K, et al. The American Journal of Clinical Nutrition. 2012;95(6):1357-64. doi:10.3945/ajcn.111.031070.
• Bioavailability of Vitamin D(2) and D(3) in Healthy Volunteers, a Randomized Placebo-Controlled Trial.
• Lehmann U, Hirche F, Stangl GI, et al.  The Journal of Clinical Endocrinology and Metabolism. 2013;98(11):4339-45. doi:10.1210/jc.2012-4287.
• Differential Effects of Oral Boluses of Vitamin D2 vs Vitamin D3 on Vitamin D Metabolism: A Randomized Controlled Trial.
• Martineau AR, Thummel KE, Wang Z, et al. The Journal of Clinical Endocrinology and Metabolism. 2019;104(12):5831-5839. doi:10.1210/jc.2019-00207.
• The Case Against Ergocalciferol (Vitamin D2) as a Vitamin Supplement.
• Houghton LA, Vieth R. The American Journal of Clinical Nutrition. 2006;84(4):694-7. doi:10.1093/ajcn/84.4.694.
• Italian Association of Clinical Endocrinologists (AME) and Italian Chapter of the American Association of Clinical Endocrinologists (AACE) Position Statement: Clinical Management of Vitamin D Deficiency in Adults.
• Cesareo R, Attanasio R, Caputo M, et al.  Nutrients. 2018;10(5):E546. doi:10.3390/nu10050546. Copyright License: CC BY
• Effect of Vitamin D2 Supplementation on 25-Hydroxyvitamin D3 Status: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.
• Brown EIG, Darling AL, Robertson TM, et al. Nutrition Reviews. 2025;:nuaf166. doi:10.1093/nutrit/nuaf166.
• Safety Profile of Vitamin D in Italy: An Analysis of Spontaneous Reports of Adverse Reactions Related to Drugs and Food Supplements.
• Maggini V, Crescioli G, Ippoliti I, et al. Journal of Clinical Medicine. 2023;12(14):4726. doi:10.3390/jcm12144726.
• Comparative Analyses of the Safety Profiles of Vitamin D Receptor Agonists: A Pharmacovigilance Study Based on the EudraVigilance Database.
• Gáll Z, Kolcsar M. Pharmaceuticals (Basel, Switzerland). 2024;17(12):1686. doi:10.3390/ph17121686.
• Micronutrients — Assessment, Requirements, Deficiencies, and Interventions.
• Allen LH.  The New England Journal of Medicine. 2025;392(10):1006-1016. doi:10.1056/NEJMra2314150.
• Vitamin and Mineral Supplements for the Primary Prevention of Cardiovascular Disease and Cancer: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force.
• O'Connor EA, Evans CV, Ivlev I, et al. JAMA. 2022;327(23):2334-2347. doi:10.1001/jama.2021.15650.

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This handout created with the assistance of OpenEvidance.com and Grammarly.com.  The OpenEvidence system leverages a comprehensive, regularly updated database that includes clinical trials, meta-reviews, regulatory drug labels, and practice guidelines to ensure reliable and accurate information. OpenEvidence has signed content agreements with NEJM, JAMA, NCCN, and more. Image from Chatgpt.com.

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