What Happens to Vitamin C in Water?

December 31, 2025 •

4 min read

According to Harvard T.H. Chan School of Public Health, vitamin C, an essential water-soluble vitamin, can be significantly destroyed by heat and light. This instability means that when vitamin C is dissolved in water, it begins a process of degradation that affects its potency over time.

Quick Summary

Vitamin C, or ascorbic acid, degrades in water through oxidation, a process accelerated by heat, light, alkaline pH, and metal ions like copper. It is most stable in acidic solutions and when kept cool, dark, and away from oxygen exposure.

Key Points

Oxidation: Vitamin C degrades in water through oxidation, especially when exposed to oxygen, heat, and light, losing its potency over time.
Heat and Cooking: High temperatures, especially boiling, significantly accelerate the breakdown of vitamin C and cause it to leach out of food into the water.
Storage Conditions: For maximum stability, vitamin C solutions and supplements should be stored in a cool, dark place and sealed in opaque containers to limit exposure to light and oxygen.
pH is Crucial: Vitamin C is most stable in acidic solutions (pH 3-5); the degradation rate increases significantly in neutral and alkaline environments.
Metal Catalysts: Certain metal ions, such as copper and iron, can act as catalysts that speed up the oxidation process of vitamin C in water.
Fresh is Best: Eating vitamin C-rich foods raw and fresh is the most effective way to consume the highest concentration of the nutrient before it has a chance to degrade.

The Chemical Instability of Vitamin C in Aqueous Solutions

Vitamin C, known chemically as ascorbic acid, is a powerful antioxidant, but it is also highly reactive and unstable when dissolved in water. This vulnerability stems from its chemical structure, which readily gives up electrons to other molecules. This characteristic is what makes it an effective antioxidant, but it is also the very reason it breaks down so easily, especially in the presence of water.

The primary culprit for the degradation of vitamin C in water is oxidation, where the molecule loses electrons. When ascorbic acid is oxidized, it first converts into a compound called dehydroascorbic acid. While dehydroascorbic acid still retains some vitamin C activity, it is far less stable and will quickly undergo irreversible degradation into other compounds with no nutritional value, like oxalic acid. This reaction is influenced by several environmental factors, including temperature, light, and the presence of oxygen or certain metal ions.

Key Factors Influencing Vitamin C Degradation

Temperature

Heat is a major accelerator of vitamin C's oxidation. When cooking vegetables by boiling, not only does the heat hasten the chemical breakdown, but the water-soluble vitamin also leaches out into the cooking water. One study found that boiling vegetables for just 10 minutes could destroy over 50% of their vitamin C content. However, as one source notes, the boiling temperature alone (around 100°C) is not high enough to instantly decompose pure ascorbic acid, but the combination of high temperature and dissolved oxygen in the water significantly promotes oxidation.

Light and Oxygen

Exposure to both light and oxygen significantly hastens the decomposition of vitamin C in water. Oxygen acts as the electron acceptor in the oxidation process, while light provides the energy to drive the reaction. This is why orange juice is often sold in opaque containers and should be stored in a cool, dark place. The more you expose the solution to air and light, the faster the vitamin C content will diminish. One study found that after 3 hours of incubation at room temperature in copper-contaminated tap water, 93% of the added ascorbic acid had oxidized.

pH Level

The pH of the aqueous solution plays a critical role in vitamin C stability. It is most stable in mildly acidic conditions (pH 3.0-5.0), and its degradation rate increases as the solution becomes more alkaline. This is a crucial consideration for commercial products, as food processing and fortification often involve altering pH levels. In alkaline solutions, oxidation happens much more rapidly, leading to a faster loss of nutritional value.

Metal Ions

Certain metal ions, particularly copper (Cu²⁺) and iron (Fe²⁺), act as catalysts that accelerate the oxidative degradation of ascorbic acid. These ions can be found in some tap water supplies, and even small concentrations can significantly speed up the breakdown of vitamin C. This is why avoiding metal utensils or cookware when preparing vitamin C-rich foods or supplements is often recommended.

Practical Ways to Preserve Vitamin C

Choose Raw and Fresh: The most reliable way to consume vitamin C is from raw, fresh fruits and vegetables, as they offer the highest concentrations.
Use Quick Cooking Methods: When cooking, opt for methods that minimize water use and cooking time, such as steaming, stir-frying, or microwaving, to retain more vitamin C.
Store Properly: Keep vitamin C supplements and juices in airtight, opaque containers and refrigerate them to slow down the degradation process.
Drink the Cooking Water: If boiling vegetables, use the cooking water in soups or sauces to reclaim the valuable water-soluble vitamins that have leached out.

The Effect of Different Conditions on Vitamin C Stability


Condition	Effect on Vitamin C	Explanation
Heat	Increases degradation speed	High temperatures accelerate the chemical reaction of oxidation.
Light	Increases degradation speed	UV light provides energy that promotes photo-degradation.
Oxygen Exposure	Accelerates oxidation	Oxygen in the air and dissolved in water acts as an electron acceptor, driving the oxidation process.
Alkaline pH	Increases degradation speed	The degradation rate increases significantly in neutral and alkaline solutions compared to acidic ones.
Acidic pH	Increases stability	Ascorbic acid is most stable in acidic solutions (pH 3-5).
Cold Storage	Increases stability	Low temperatures inhibit the chemical reactions that cause degradation.
Metal Ions (Cu, Fe)	Accelerates oxidation	These metals catalyze the oxidation process, even at low concentrations.

Conclusion

While vitamin C is a vital nutrient, its presence in water is transient and highly dependent on environmental factors. It is a fragile molecule that succumbs to oxidation, a process accelerated by heat, light, alkaline conditions, and metal catalysts. Whether preparing fresh food or dissolving a supplement, understanding the science behind this instability is key to preserving its nutritional benefits. Storing products correctly, using appropriate cooking methods, and consuming fresh sources are the most effective strategies for maximizing your intake of this essential vitamin. By taking these simple steps, you can ensure that the vitamin C you consume remains potent and effective in supporting your health.

LivOn Labs offers additional tips on cooking to retain vitamin C content.

Frequently Asked Questions

Yes, vitamin C can be destroyed in boiling water, but not solely by the temperature. The combination of heat, oxygen dissolved in the water, and the cooking time accelerates its oxidation and breakdown.

Vitamin C can degrade quite rapidly in tap water. The presence of metal ions like copper and iron, as well as the pH and dissolved oxygen in tap water, can significantly accelerate the oxidation process.

The stability is short-lived. Once dissolved, vitamin C starts degrading immediately due to exposure to air and light. A solution can lose a significant portion of its potency within a few hours, especially if left at room temperature.

You can slow down the degradation by limiting exposure to its main triggers. Use cold water, minimize contact with air, keep it in an opaque container, and avoid prolonged storage.

Orange juice is packaged in opaque cartons to protect the vitamin C from light-induced degradation. Light exposure accelerates the oxidation of ascorbic acid, which would reduce the vitamin content over time.

Yes, you should. Since vitamin C is water-soluble, a significant amount of it leaches out of the vegetables and into the cooking water. Consuming this water, for instance in soups or gravies, helps you reclaim the lost nutrients.

Adding lemon juice to water creates a more acidic environment. Vitamin C is more stable in acidic solutions, so this can help slow its degradation compared to neutral or alkaline water.