Is Vitamin B12 Light Sensitive? A Complete Guide

November 13, 2025 •

5 min read

Research has demonstrated that vitamin B12 in aqueous solutions is photolabile, meaning it degrades when exposed to light. This makes vitamin B12 light sensitive, particularly in liquid formulations like injectable solutions and oral drops, but the impact varies depending on the form and intensity of light exposure.

Quick Summary

Vitamin B12 degrades upon light exposure, a process called photolysis, which affects its potency. Liquid forms like injections are most vulnerable, while dry oral supplements are more stable. Proper storage is crucial to preserve its effectiveness.

Key Points

Light Sensitivity: Vitamin B12 is sensitive to light, a process called photolysis that breaks down the vitamin and reduces its potency.
Liquid vs. Dry: Liquid forms of B12, such as injections and drops, are significantly more vulnerable to light degradation than dry, solid forms like tablets.
Active Forms are Vulnerable: The biologically active forms of B12, methylcobalamin and adenosylcobalamin, are particularly sensitive to UV light and degrade quickly.
Proper Storage is Key: To maintain potency, store B12 in cool, dark places in opaque containers, and keep liquid forms refrigerated if specified by the manufacturer.
Protecting Injections: For B12 injections, it is recommended to wrap the vials in aluminum foil and handle them quickly to minimize light exposure.
Avoid High-Exposure Areas: Never store vitamin B12 in sunlit areas, bathrooms, or kitchen spaces with high temperature and humidity fluctuations.

The Science of B12 Photolysis

Photolysis is the chemical decomposition of a substance by light. For vitamin B12, this process breaks down the complex cobalamin molecule, particularly affecting the cobalt-carbon bond in its biologically active forms. This degradation leads to a loss of the vitamin's potency and can convert it into less effective or inactive forms.

Forms of Cobalamin and Their Stability

Vitamin B12 exists in several forms, which have different levels of light sensitivity:

Methylcobalamin (MeCbl) and Adenosylcobalamin (AdCbl): These are the two primary active forms of B12 in the body and are extremely sensitive to UV light. Studies show they can rapidly degrade and convert to other forms within seconds of UVA exposure in aqueous solutions.
Cyanocobalamin (CNCbl): A synthetic, more stable form often used in supplements. While less sensitive than the active forms, it is still photolabile in solutions and converts to hydroxocobalamin (OHCbl) upon exposure to UV radiation.
Hydroxocobalamin (OHCbl): Another form of B12 that is relatively more photostable than MeCbl and AdCbl. It is the primary degradation product of other cobalamins and is also used therapeutically.

The chemical structure of cobalamins makes them susceptible to breakdown by light, and this sensitivity is most pronounced when the vitamin is in a liquid state. Dry, crystalline B12 is remarkably stable to light and heat, but once dissolved, its degradation rate increases dramatically with light exposure. This is why the handling and storage of different B12 products require varying levels of caution.

Factors Influencing B12 Light Sensitivity

Several factors determine the extent to which vitamin B12 is affected by light:

Light Intensity and Wavelength: The rate of photolysis is directly related to light intensity. High-intensity sources like direct sunlight cause rapid degradation, especially in the UV and short-wavelength visible light regions. Lower-intensity artificial light also causes degradation over time, but at a slower rate.
Presence of Other Compounds: The stability of B12 can be affected by other substances in a solution. For example, certain B vitamins, like riboflavin (B2), and vitamin C can accelerate the photodegradation of B12. This is a key consideration for combination supplements.
Formulation (Liquid vs. Dry): The most significant factor is the vitamin's state. As mentioned, liquid solutions are highly vulnerable, whereas dry tablets, powders, or capsules are much more protected. This difference explains why most oral B12 supplements are sold as tablets or in opaque bottles.

Practical Implications for B12 Supplements

Understanding B12's light sensitivity is crucial for maintaining the efficacy of supplements. The method of delivery significantly impacts how vulnerable the vitamin is to light damage.

Protecting Oral and Sublingual B12

For oral supplements, the primary goal is to minimize light exposure during storage. Most reputable manufacturers package B12 tablets and capsules in opaque, amber-colored bottles to block light.

Store bottles in a cool, dark place, away from windows and heat sources like stovetops or ovens.
Keep the lid tightly sealed to prevent exposure to air and moisture, which can also contribute to degradation.
Avoid storing supplements in a bathroom medicine cabinet, as fluctuating humidity and temperature can be detrimental.

Handling B12 Injections

Injectable B12 is in a liquid, light-sensitive form. Proper handling is critical to ensure potency.

Storage: Unopened B12 injection vials, especially hydroxocobalamin, often require refrigeration to maintain stability. Always check the manufacturer's specific instructions. Store them in their original box or wrap vials in aluminum foil to block all light.
Handling: When preparing an injection, minimize the time the liquid is exposed to light. Draw the dose into the syringe promptly and inject it quickly. Normal usage, where the vial is exposed for a couple of minutes, is unlikely to cause significant degradation.
Pre-filled Syringes: Never store pre-filled syringes for later use. This exposes the liquid B12 to light, even from normal room lighting, and can compromise its effectiveness over time.

Comparison Table: B12 Stability by Form


Feature	B12 Injections (Liquid)	B12 Drops (Liquid)	B12 Tablets/Capsules (Dry)
Light Sensitivity	High, especially active forms like methylcobalamin.	High, depends on light intensity and exposure time.	Low, protected by solid form and packaging.
Primary Risk	Rapid photolysis during storage or handling, leading to potency loss.	Potential degradation if stored improperly or in transparent bottles.	Very low, as light struggles to penetrate the solid form.
Storage Recommendations	Refrigerate (if required) in opaque packaging; wrap in foil once opened.	Keep in original amber or opaque bottle, in a cool, dark place.	Store in a cool, dry place, away from light and heat.
Handling Best Practices	Inject shortly after drawing from vial; cover vial with foil.	Keep lid tightly closed and minimize exposure to light.	Simply follow normal supplement storage guidelines.
Common Packaging	Amber glass vials.	Amber or opaque plastic bottles.	Opaque plastic bottles or blister packs.

How to Properly Store Your Vitamin B12

Read the Label: Always follow the manufacturer's specific storage recommendations, as they can vary by formulation. Some liquid drops or certain forms like hydroxocobalamin may require refrigeration, while standard tablets are fine at room temperature.
Use Opaque Containers: Keep your supplements in their original, opaque packaging. These bottles are specifically designed to block light and protect the product from degradation.
Choose a Cool, Dark Location: A linen closet, drawer, or kitchen cabinet (away from heat sources like ovens) is ideal. Avoid bathrooms and kitchens where temperature and humidity fluctuate significantly.
Minimize Exposure Time: For liquid products and injections, only expose the vial or bottle to light for as long as necessary. Put it back in its dark storage location immediately after use.
Consider Dry Forms: If you are concerned about stability, opt for dry forms of B12 over liquids. Powders, capsules, or sublingual tablets are all more stable in the presence of light than liquid solutions.

Conclusion

In summary, yes, vitamin B12 is light sensitive, particularly in liquid forms and when exposed to UV radiation. Photolysis can reduce the potency of B12, but its impact depends on the specific form of cobalamin, the intensity and type of light, and the presence of other compounds. By following proper storage practices—using opaque containers, choosing cool and dark locations, and minimizing exposure for liquid products—you can effectively protect your vitamin B12 and ensure its maximum effectiveness.

For more information on the photolytic properties of cobalamins, see this article by ScienceDirect.

Frequently Asked Questions

Most dry oral B12 supplements in tablet or capsule form do not require refrigeration and are stable at room temperature. However, some liquid drops or injectable forms, particularly those containing hydroxocobalamin, may need to be refrigerated. Always check the product label for specific instructions.

No, you should not store B12 in syringes for later injections. Once drawn from the vial, the liquid B12 is exposed to light, which can cause it to degrade rapidly. Prepare and inject the dose promptly to ensure maximum potency.

If a liquid B12 supplement is left in direct sunlight, its potency will be significantly reduced due to photolysis. One study found that intense sunlight can cause a 10% loss of crystalline B12 in solution within 30 minutes. Dry tablets are much less affected but should still be stored in a cool, dark place.

B12 bottles are dark or amber-colored to protect the contents from light, which can degrade the vitamin over time. This opaque packaging is a standard practice to preserve the supplement's stability and effectiveness.

No, storing supplements in a bathroom is not recommended. Bathrooms experience frequent fluctuations in temperature and humidity, which can negatively impact the stability and shelf life of vitamins, including B12.

No, different forms of B12 have varying light sensitivities. The active forms, methylcobalamin and adenosylcobalamin, are the most vulnerable, while hydroxocobalamin is more stable. Cyanocobalamin is less sensitive than the active forms but still degrades in light.

Yes, some studies suggest that vitamin C (ascorbic acid) can accelerate the photodegradation of B12 in liquid formulations. This interaction is a key consideration for combination supplements containing both vitamins.