Cooking, Processing and Storage: How Much Vitamin Content Foods Keep
What laboratory studies and nutrition sources show about vitamin losses from cooking, freezing, processing and storage, why results differ by vitamin and food, and why there is no single rule.
Content last updated . This page has not been medically reviewed.
Proper evidence not found for one table that gives the percentage of every vitamin kept by every food and method. I searched PubMed for vitamin retention in cooking, freezing and storage and read the studies below plus the NIH Office of Dietary Supplements (ODS, US) fact sheets.
Evidence labels used here
Laboratory measurement means vitamin levels measured in specific foods under test conditions. It says nothing about health outcomes. Reference-source statement means what a nutrition fact sheet reports.What was measured
| Question | What the source found | Type |
|---|---|---|
| Vitamin C and cooking method (blanching, boiling, microwaving, steaming; several vegetables) | Vitamin C retention ranged from 0.0 to 91.1% across all cooked samples; generally higher after microwaving and lowest after boiling [1] | Laboratory measurement |
| Fat-soluble vitamins in cooked vegetables | Cooked vegetables occasionally had higher contents of alpha-tocopherol and beta-carotene than fresh ones, depending on the vegetable [1] | Laboratory measurement |
| Vitamin K and microwaving | Greatest loss in crown daisy and mallow, least loss in spinach and chard [1] | Laboratory measurement |
| Fresh vs frozen produce (eight fruits and vegetables; vitamin C, riboflavin, alpha-tocopherol, beta-carotene) | Overall, vitamin content of frozen was comparable to and occasionally higher than fresh; beta-carotene decreased drastically in some commodities [2] | Laboratory measurement |
| Folate, boiling vs frying (Fijian vegetables) | Folate loss 10 to 64% on boiling and 1 to 36% on frying; the boiling loss was found in the cooking water, mostly from leaching rather than heat damage [3] | Laboratory measurement |
| Folate forms in Brazilian brassica vegetables | Retention depended on the food, the folate form and the cooking method [4] | Laboratory measurement |
| Vitamin E in beans, frozen or canned products prepared for eating | Cooking cut total tocopherols by 13 to 28% and vitamin E activity by 17 to 31%; after 12 months' storage the products were 13 to 53% (tocopherols) and 23 to 60% (vitamin E activity) lower than fresh seeds [5] | Laboratory measurement |
What the nutrition fact sheets add
- Thiamin (B1). The ODS says thiamin dissolves in water, so a significant amount is lost when cooking water is thrown out; bread has 20% to 30% less thiamin than its raw ingredients; unenriched white rice has one-tenth the thiamin of unenriched brown rice. [6]
- Riboflavin (B2). About twice as much riboflavin is lost in the cooking water when foods are boiled as when they are prepared in other ways, such as steaming or microwaving. [7] Ultraviolet and visible light can rapidly inactivate riboflavin. [7] The NHS (UK) suggests keeping riboflavin-rich foods out of direct sunlight. [8]
- Pantothenic acid (B5). Food processing can cause losses of 20% to almost 80%. [9]
- Biotin. Cooking is helpful here: it denatures avidin in raw egg whites, which otherwise prevents biotin absorption. [10]
- Vitamin K. The ODS notes that vitamin K from plant foods is absorbed better when eaten with some fat. [11]
Reading the evidence
- Water-soluble vitamins move into water. The folate study found the loss from boiling was accounted for in the cooking water, so the vitamin was not destroyed but lost if the water was discarded. [3] The ODS says the same about thiamin. [6] That describes where the vitamin went, not a personal instruction.
- Averages hide big ranges. Vitamin C retention ranged from 0.0 to 91.1% in one study. [1] A single figure such as "cooking destroys half" is not supported.
- Frozen is not worse by default. In the fresh-versus-frozen study, vitamin content was comparable to and occasionally higher than fresh counterparts. [2] That study compared refrigerated and frozen storage only.
- Studies are small and specific. These are laboratory tests on a few foods in Korea, the US, Fiji, Brazil and Poland. They do not show differences in health. Biomarker or composition change is not a health outcome.
Warfarin and steady eating patterns
If you take warfarin, the NHS says you can still eat foods high in vitamin K, such as broccoli, spinach and other green leafy vegetables, but you should talk to your warfarin clinic about changes. [12] Because cooking can change vitamin K content differently for different vegetables [1], ask your anticoagulation clinic before changing how you prepare or how much you eat. See Foods high in vitamin K.Where to go next
- Food tables for individual vitamins: Foods high in vitamin C, Foods high in folate, and Foods high in biotin and other B vitamins.
- Added vitamins: Fortified and enriched foods.
- Food versus pills: Food-first nutrition and Food vs supplement sources.
- If you are worried about low vitamin intake, ask a clinician; do not self-diagnose a deficiency from symptoms (Deficiency testing and its limits).
Frequently asked questions
Does cooking destroy vitamins?
Some are reduced and some are not, depending on the vitamin, food and method. In one study vitamin C retention in cooked vegetables ranged from 0.0 to 91.1%. [1]
Is boiling worse than steaming or microwaving?
For vitamin C the lowest retention was recorded after boiling in one study. [1] The ODS says about twice as much riboflavin is lost to cooking water when boiling as with other methods. [7] For vitamin K the effect of microwaving differed between vegetables. [1]
Are frozen vegetables less nutritious than fresh?
In a study of eight fruits and vegetables, vitamin content of frozen was comparable to and occasionally higher than fresh, though beta-carotene fell sharply in some. [2]
Are vitamins lost when food is stored?
In a study of beans, frozen and canned products prepared after 12 months' storage had 13 to 53% less total tocopherols than fresh seeds. [5] Light can also reduce riboflavin. [7]
Should I take supplements because cooking removes vitamins?
That is not shown by the sources read here. Talk to a clinician or pharmacist about whether a supplement suits you, and see Multivitamins and Medication interactions.