What vitamin may be destroyed in heat during cooking?

November 27, 2025 •

3 min read

Boiling vegetables can reduce Vitamin C content by 50% or more, according to the National Institutes of Health, highlighting the impact of cooking on nutrients. Understanding which vitamin may be destroyed in heat is crucial to preserving nutritional value.

Quick Summary

Cooking methods, especially those using high heat and water, reduce certain heat-sensitive vitamins. Vitamins C, B1 (Thiamine), and B9 (Folic Acid) are vulnerable to degradation. Steaming, microwaving, and shorter cooking times can minimize loss.

Key Points

Vitamin C and B vitamins are heat-sensitive: Water-soluble vitamins like Vitamin C, Thiamine (B1), and Folic Acid (B9) are vulnerable to degradation and leaching during cooking.
Boiling causes the most nutrient loss: This method combines high heat and water, leaching water-soluble vitamins into the cooking water which is often discarded.
Steaming and microwaving preserve more vitamins: These methods use less water and shorter cooking times, retaining more water-soluble vitamins compared to boiling.
Fat-soluble vitamins are more stable: Vitamins A, D, E, and K are generally less affected by heat, but prolonged exposure to high temperatures can cause some loss.
Smart cooking techniques matter: To minimize vitamin loss, use minimal water, cook for shorter periods, cut vegetables just before cooking, and reuse cooking liquids.
Storage conditions impact vitamins: High heat, light, and humidity can accelerate the degradation of vitamins, both in food and supplements.
A balanced diet is key: Eating a mix of both raw and cooked foods is the best strategy to ensure a broad spectrum of vitamins and other nutrients.

The Sensitivity of Water-Soluble Vitamins

Water-soluble vitamins, including Vitamin C and the B-complex vitamins, are most susceptible to degradation during cooking due to their chemical structure and solubility. When heated in water, these vitamins can leach out into the cooking liquid. If the water is discarded, the nutrients are lost.

Vitamin C: The Most Fragile Nutrient

Vitamin C, or ascorbic acid, is most vulnerable to heat, light, and air. Its degradation starts at 30°C (86°F) and accelerates with higher heat. Boiling can cause substantial losses, with some studies showing reductions of 50% or more in broccoli and spinach. Eating raw Vitamin C-rich fruits and vegetables, like oranges and bell peppers, is often recommended for maximum intake.

B Vitamins: A Complex Vulnerability

Not all B vitamins are equally sensitive, but several are susceptible to heat and water.

Vitamin B1 (Thiamine): This vitamin is highly heat-sensitive and can be destroyed during prolonged high temperatures. It is also water-soluble, so boiling can cause a considerable loss. Boiling could cause a thiamine loss of 20–80%, according to a National Institutes of Health study.
Vitamin B9 (Folic Acid): Folic acid is also a water-soluble vitamin easily destroyed by heat. Boiling can lead to significant folate loss, with one study reporting up to a 50% loss in certain foods after 15 minutes of boiling.
Other B Vitamins: While less vulnerable than thiamine and folate, other B vitamins like riboflavin (B2) can also be affected by heat and light during processing and cooking.

Fat-Soluble Vitamins and Heat

Fat-soluble vitamins (A, D, E, and K) are generally more stable when exposed to heat. However, prolonged cooking at very high temperatures, especially deep-frying, can still lead to some degradation. The presence of oil in cooking can sometimes aid in the absorption of these vitamins but can also contribute to their loss if the cooking is done improperly.

Comparison of Cooking Methods for Nutrient Retention

The table below compares common cooking methods and their effect on nutrient retention.


Cooking Method	Effect on Water-Soluble Vitamins (C, B1, B9)	Effect on Fat-Soluble Vitamins (A, D, E, K)	Recommended Practice
Boiling	High loss due to heat and leaching into water.	Minimal loss unless prolonged or at extremely high heat.	Use minimal water and reuse cooking liquid for soups/sauces.
Steaming	Low to moderate loss, as food does not contact water.	Minimal loss, a good option for most.	Best method to retain water-soluble vitamins; cook for a short time.
Microwaving	Low to moderate loss due to short cooking times and minimal water.	Low loss; can enhance the absorption of some nutrients.	Cook with minimal water and cover food to trap moisture and nutrients.
Stir-Frying/Sautéing	Low to moderate loss due to quick cooking time, though high heat can degrade some.	Good retention; can increase absorption of fat-soluble vitamins.	Use a small amount of healthy oil and cook quickly over medium-high heat.
Roasting/Baking	Moderate loss, as longer cooking times expose nutrients to heat.	High retention; preserves minerals and fat-soluble vitamins well.	Cook at lower temperatures for shorter periods and consider leaving skins on.

Strategies to Minimize Vitamin Loss in Your Cooking

Simple kitchen habits can significantly increase the vitamins you get from food.

Prioritize Fast and Gentle Cooking: Use methods that use less water and shorter cooking times, such as steaming or microwaving. Quick sautéing or stir-frying is also preferable to prolonged boiling.
Use Cooking Liquid: Save the nutrient-rich water for soups, stews, or sauces if you boil vegetables. This reincorporates the leached vitamins.
Cut Later: Chop fruits and vegetables just before cooking or serving to minimize their exposure to air, which promotes oxidation and nutrient loss. Larger pieces reduce vitamin loss.
Cook for Shorter Times: Avoid overcooking vegetables until they are mushy. Tender-crisp is often the best for flavor and nutrient preservation.
Consider Raw Foods: Incorporate raw foods like salads and fresh fruit to ensure you get the full vitamin content without heat degradation.
Store Properly: Keep fresh produce in a cool, dark place to slow down vitamin decay.

Conclusion

Be mindful of how heat can degrade vitamins, especially water-soluble ones like Vitamin C, Thiamine (B1), and Folic Acid (B9). Choosing cooking methods like steaming, microwaving, or stir-frying, can minimize nutrient loss. Practices like using cooking water and storing produce correctly can also make a significant difference. Understanding which vitamins are most at risk from heat can help make informed choices to protect nutritional value.

Frequently Asked Questions

Vitamin C is the most easily destroyed vitamin by heat, light, and oxygen. Its water-soluble nature makes it highly susceptible to leaching into cooking water, especially during boiling.

Not all vitamins are equally affected by cooking. Water-soluble vitamins like B-complex and C are the most vulnerable, while fat-soluble vitamins (A, D, E, K) are more stable and less likely to be significantly destroyed by heat.

Steaming is generally better for retaining nutrients than boiling. Since the food does not come into direct contact with water, there is less leaching of water-soluble vitamins.

To prevent vitamin loss, use minimal water for cooking, cook for shorter periods, reuse cooking liquids, and choose gentle cooking methods like steaming or microwaving. Cutting vegetables just before cooking also helps minimize surface area exposure.

Microwaving is a nutrient-friendly cooking method. Its short cooking time and minimal use of water mean less vitamin destruction compared to methods like boiling.

Yes, repeated reheating of food can deplete nutrient levels, especially those of heat-sensitive vitamins like C and folate. Storing food properly and consuming it fresh when possible is recommended to retain nutrients.

Fat-soluble vitamins are more stable than water-soluble ones but are not completely unaffected. High-temperature cooking, particularly deep-frying, can still cause some degradation.