The Surprising Truth: Is Folate Destroyed by Sunlight?

October 17, 2025 •

3 min read

According to research, UV radiation from sunlight can cause the degradation of folate in vitro and impact circulating levels in humans, particularly when taking folic acid supplements. This raises the important question: Is folate destroyed by sunlight?, and if so, what are the implications for our diet and nutrient intake? (Fact-check needed)

Quick Summary

Sunlight, particularly its ultraviolet (UV) component, is a known factor in the degradation of folate in both food and supplement forms. Natural folates and synthetic folic acid are susceptible to light, heat, and oxygen, which contribute to nutrient loss. Implementing proper storage techniques and choosing protective packaging is essential to maximize the retention of this vital B vitamin.

Key Points

UV Radiation Degrades Folate: Both naturally occurring folates and synthetic folic acid are chemically sensitive and can be broken down by UV light from the sun.
Folic Acid Is More Vulnerable: The synthetic form, folic acid, is particularly susceptible to photodegradation compared to some natural folate forms.
Storage Practices Are Key: To minimize nutrient loss, store folate-rich foods and supplements in cool, dark places and use opaque or protective containers.
Cooking Methods Influence Retention: Cooking with less water and for shorter periods, like steaming or microwaving, preserves more folate than boiling.
Sunlight's Effect on Serum Folate Varies: While some studies show decreases in serum folate with high sun exposure, especially in supplement users, the effect can vary depending on individual health and dietary factors.
Mindful Handling Is Important: Being aware of folate's instability allows you to make better choices in storing and preparing food to maintain its nutritional value.

The Chemical Reality: Folate's Photosensitivity

Folate is a group of water-soluble B vitamins, with folic acid being the synthetic form. Both natural folates in food and synthetic folic acid can degrade due to environmental factors like light, heat, and oxygen. UV radiation from sunlight is a key factor in breaking down the folate molecule. This photosensitivity is important for maintaining nutritional value.

The Mechanisms of UV-Induced Folate Degradation

UV light causes the pterin ring in folate to absorb energy, leading to a photo-induced electron transfer. This energy breaks the C9-N10 bond, creating inactive photoproducts. Other molecules, like riboflavin, can also speed up this degradation.

Impact on Folate in Foods and Supplements

Sunlight exposure can reduce the folate content in foods and supplements. This is a concern during storage and preparation. For example, leafy greens or transparent bottles of supplements in direct light can lose folate. Manufacturers of fortified foods use protective packaging or over-fortify to account for this instability.

Folate Retention by Cooking Method

Folate is water-soluble and heat-sensitive, making cooking methods and storage conditions impactful on its retention. Here's a comparison:


Cooking Method	Description	Folate Retention (Relative)	Notes
Steaming	Minimal water contact.	High	Best for preserving water-soluble vitamins.
Microwaving	Quick cooking, little water.	High	Quick cooking minimizes loss.
Boiling	Fully submerged in water.	Low	Folate leaches into water.
Roasting	Dry heat.	Moderate to High	No water leaching, but heat can cause some degradation.

Can Sunlight Affect the Body's Folate Levels?

While folate degradation in food and supplements due to sunlight is clear, the effect of sun exposure on circulating folate levels in humans is more complex.

Supplement users: A study found a link between increased solar UV exposure and lower serum folate in women taking folic acid supplements. Folic acid may be more vulnerable to photodegradation than natural folate in individuals with high sun exposure.
Healthy individuals: A different study found no significant effect on blood folate levels in healthy volunteers exposed to sunlight or sunbeds. This might be due to dietary intake and the body's ability to compensate.
Localized skin effects: UV exposure can also cause localized folate changes in the skin.

Practical Strategies for Maximizing Folate Intake

Protecting folate from light, heat, and oxygen is key for maximizing intake.

Food Storage

Refrigerate: Store fresh produce in the refrigerator to slow degradation.
Airtight containers: Use sealed containers to limit oxygen exposure.
Store away from light: Keep light-sensitive foods and supplements in dark containers and away from direct sunlight.

Cooking and Preparation

Better cooking methods: Steam or microwave vegetables instead of boiling to reduce nutrient leaching.
Minimal chopping: Cut vegetables just before cooking to limit exposure to oxygen and light.
Shorter cooking times: Cook vegetables quickly to minimize heat exposure.
Use cooking liquid: If boiling, save the water for other uses to retain some folate.

Conclusion: Protect Your Folate Intake

Sunlight does destroy folate. Both natural and synthetic forms are sensitive to UV light, leading to a loss of nutritional value. While the effect of sun exposure on blood folate levels in healthy individuals may vary, it is a significant factor in the degradation of folate in foods and supplements, particularly for those with higher needs. By being mindful of folate's sensitivity and adopting proper storage and cooking practices, you can help ensure adequate intake of this important nutrient.

Resources

Fondation Louis Bonduelle: Offers useful information on vitamins and nutrient preservation, including how to protect them from light and heat. https://www.fondation-louisbonduelle.org/en/nutrient/the-difference-between-vitamin-b9-and-folic-acid/

Frequently Asked Questions

Yes, sunlight can destroy the folate in leafy greens. Leaving vegetables exposed to direct sunlight, such as on a countertop, will accelerate the breakdown of this nutrient. For best results, store them in the refrigerator, away from light.

Yes, it is crucial to store folate and folic acid supplements in a dark place. Many vitamins, including B vitamins, are sensitive to light and can degrade when exposed. Keeping them in an opaque container in a cupboard protects their potency.

Yes, folate is also sensitive to heat and is water-soluble. Boiling vegetables, for instance, can cause a significant amount of folate to leach into the cooking water, which is often discarded. Using methods like steaming or microwaving helps retain more of the nutrient.

The stability varies. The natural forms of folate are generally less stable and more susceptible to oxidation, while the synthetic folic acid is more stable chemically. However, some natural folates, like 5-methyltetrahydrofolate, are more stable under UV exposure than folic acid.

The amount of folate lost during cooking can vary widely depending on the food and method. For example, boiling vegetables can result in significant losses, while steaming can result in minor losses. Cooking time, temperature, and water quantity all play a role.

For most healthy people, normal sun exposure is unlikely to cause a deficiency that cannot be corrected by diet. However, individuals with high sun exposure or who are taking folic acid supplements may see a reduction in serum folate levels due to photodegradation.

The best methods for retaining folate are steaming and microwaving, as they use minimal water and shorter cooking times. If you do boil, consider using the nutrient-rich cooking liquid in a soup or sauce.