How to Choose a Quality Vitamin D3: What to Look for on the Label

Vitamin D3 is one of the cheapest and at the same time most «varied» supplements: drops, capsules, chewable tablets, sprays, doses from 400 to 10,000 IU and more. The editorial team explains how to read the label to understand the real dose, form, and origin of the vitamin, and what signs of quality are worth paying attention to.

Units of measurement: IU, micrograms, and percentage of the norm

The first thing you need to find on the label is the content of vitamin D per serving. It is indicated in micrograms (mcg, µg) or in international units (IU). The ratio is simple and unchanging: 1 mcg of vitamin D corresponds to 40 IU. So 10 mcg is 400 IU, 25 mcg is 1000 IU, 50 mcg is 2000 IU.

In EU countries, the main unit on the label is micrograms, and international units are often given in parentheses. American products, on the contrary, traditionally indicate IU. Confusion of units is a common cause of errors: a person accustomed to «1000» may not notice that a European label says «100 mcg», that is, 4000 IU.

The percentage of the reference value on European labels can be misleading. The reference value for labeling in the EU is only 5 mcg (200 IU), so a product with 25 mcg shows «500%», and one with 100 mcg shows «2000%». Such figures do not mean that the dose is dangerous, but they also do not indicate a «stronger» product — this is only a consequence of the low base for the calculation.

To assess safety, be guided by the upper permissible limit established by the US Institute of Medicine and EFSA for adults: 100 mcg (4000 IU) per day from all sources. Higher doses are appropriate only as prescribed by a doctor.

D3 or D2 and where the raw material comes from

The label must indicate the form of the vitamin: cholecalciferol (D3) or ergocalciferol (D2). The meta-analysis by Tripkovic and co-authors (2012) showed that vitamin D3 raises the blood level of 25(OH)D more effectively than D2, especially with infrequent intake of large doses. Therefore, for most people D3 is the better choice.

The source of the raw material is also worth checking. Traditionally, vitamin D3 is obtained from lanolin — the fat of sheep’s wool, which is irradiated with ultraviolet light. Such a vitamin is not vegan, although the animals are not killed in the process. For vegans there is D3 from lichen; such products usually have a corresponding label or a vegan product certificate.

Vitamin D2 is obtained from yeast or fungi irradiated with ultraviolet light, and it was traditionally the option for vegans. With the appearance of D3 from lichen, this advantage has lost its relevance, but D2 still appears in some products and prescription preparations.

• Cholecalciferol (D3) from lanolin— the most common, inexpensive, not vegan.
• Cholecalciferol (D3) from lichen— vegan, usually more expensive.
• Ergocalciferol (D2)— of plant origin, somewhat less effective at raising 25(OH)D.

The vitamin D in cod liver oil is natural D3 together with vitamin A. In such products it is worth checking the vitamin A content as well, since with long-term intake of large amounts it can accumulate, which is especially important for pregnant women.

Dosage form: oil, dry form, drops

Vitamin D is fat-soluble, so it is traditionally produced in an oil solution — in soft gelatin capsules or drops. The carrier oil (olive, sunflower, MCT oil) simultaneously ensures the stability of the vitamin and aids absorption. Regardless of the form, the vitamin is better taken with a meal that contains fats.

Dry forms — tablets, hard capsules, powders — contain vitamin D in the form of a microencapsulated powder applied to a carrier. They are convenient as part of multivitamins and mineral complexes. Provided they are taken with food, for most people there is no significant clinical difference between a quality dry and an oil form.

Drops allow flexible dose selection, but here it is important to read carefully how much vitamin is contained in one drop, not in a milliliter. Some products contain 400 IU per drop, others 1000 IU and more. An error in the conversion can change the dose several-fold, which is especially dangerous for children.

Chewable tablets and gummies appeal to those who do not like swallowing capsules, but they often contain sugar, sweeteners, and dyes. In addition, for «gummy» forms it is more difficult to ensure the accurate vitamin content throughout the entire shelf life.

Dose per serving and combinations

Look not only at the figure but also at the serving size: some products indicate the dose for two capsules or several drops. For prevention in adults, a product with 400–2000 IU (10–50 mcg) per serving is sufficient. Capsules with 5000 and 10,000 IU are intended for treating a deficiency under a doctor’s supervision or for non-daily intake, and they should not be taken daily without a prescription.

A popular combination is vitamin D3 with vitamin K2 (menaquinone, often in the form of MK-7). It is justified by the fact that K2 participates in activating the proteins that direct calcium into the bones. A theoretical basis exists, but there is no convincing clinical evidence of the advantage of such a combination over vitamin D alone for the prevention of fractures or vascular calcification. People taking warfarin and other vitamin K antagonists can use products with K2 only after consulting a doctor.

Combinations with calcium, magnesium, and zinc are also common. They are convenient, but it is worth considering that calcium from supplements in high doses has its own risks, for example kidney stones, and most people better obtain calcium from food.

The main rule: sum up all the vitamin D from all the products you take — multivitamins, sports complexes, fortified foods. It is easy to get two or three doses from different jars without even noticing it.

Dosing accuracy, storage, and certification

Dosing accuracy is a real problem. A study by LeBlanc and co-authors (2013), which analyzed over-the-counter and compounded vitamin D preparations in the US, showed that the actual vitamin content in the pills varied over a very wide range relative to what was declared on the label, and in some products it differed even between tablets of the same package.

This is exactly why independent certification has practical value. USP Verified or NSF marks indicate that the product has been tested for compliance with the declared content and the absence of contaminants. For athletes who undergo doping control, Informed Sport or NSF Certified for Sport certificates are appropriate, as they additionally test for banned substances.

Vitamin D is sensitive to light, heat, and oxygen. Quality products are packaged in opaque or dark bottles, and the label indicates the storage conditions. Do not leave the jar in a car in summer or on a windowsill: this accelerates the destruction of the vitamin.

• Find the content per serving in mcg and IU.
• Make sure the form is cholecalciferol (D3).
• Check the source of the raw material if you are vegan.
• Assess the excipients, especially in chewable forms.
• Look for the batch number, expiration date, and independent certification.

Editorial conclusions

A quality vitamin D3 is above all a clear label: the content in micrograms and IU per serving, the cholecalciferol form, the source of the raw material, and clear storage conditions.

For prevention, 400–2000 IU per day is sufficient for most adults; products with very high doses are intended for treating a deficiency under a doctor’s supervision. Combinations with K2 or minerals are convenient but have no proven advantages for everyone.

Independent certification helps to avoid products with an inaccurate dose, which for vitamin D is a real problem.

Our articles «How to Choose a Quality Magnesium: What to Look for on the Label», «Vitamin D3 after 40», and «The History of Vitamin D3: How the Supplement Became Popular» will help continue the topic.

References

1. Tripkovic L, Lambert H, Hart K, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr. 2012;95(6):1357–1364.
2. LeBlanc ES, Perrin N, Johnson JD Jr, Ballatore A, Hillier T. Over-the-counter and compounded vitamin D: is potency what we expect? JAMA Intern Med. 2013;173(7):585–586.
3. Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington (DC): National Academies Press; 2011.
4. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the tolerable upper intake level of vitamin D. EFSA J. 2012;10(7):2813.
5. Regulation (EU) No 1169/2011 of the European Parliament and of the Council on the provision of food information to consumers. Official Journal of the European Union. 2011.
6. Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266–281.