Vitamins supplements are commonly taken by many people to treat a variety of health problems. Over time, however, vitamins can degrade, causing them to become chemically altered. Although vitamin C degrades, it is not toxic. The speed with which vitamin C degrades depends on a number of factors, and even expired vitamin C is "safe," though it may not be effective.
How Does Vitamin C Degrade?
Vitamin C is also known as ascorbic acid or ascorbate. It can undergo a type of chemical reaction known as oxidation, which changes its chemical form. The oxidized product of vitamin C is known as dehydroascorbic acid, or DHAA. Although this compound can be converted back into vitamin C, that chemical reaction does not occur naturally.
Product Quality Affects Shelf-Life
Although DHAA isn't toxic, it does not function effectively as vitamin C, meaning that over time, vitamin C supplements become less potent. However, different vitamin C supplements turn into DHAA at different rates. One factor that controls this is the initial quality of the supplement. Supplements that are packaged with very little moisture and are mostly free of any oxidized compounds will break down more slowly than poor quality supplements. However, there are no large-scale studies that have tested the degradation of different kinds of vitamin C, so it is not known which brands are the "best" in terms of expiration date.
Storage Conditions Matter
Another thing that affects how quickly a vitamin C supplement is broken down is how it is stored. Once the container is open, the supplement will begin to degrade more quickly, so unopened vitamin C supplements have a longer shelf-life than opened ones. Keeping vitamins in the bathroom or kitchen, where the humidity can rise, can increase the rate at which they degrade. Vitamins should be stored in a cool and dry part of the house, such as the bedroom.
Considerations for Taking Vitamin C
Not all vitamin C supplements have printed expiration dates, and you can still take old vitamin C tablets. However, if they have changed color or begun to dissolve, they won't be as effective. Do not take higher doses of the supplement to counteract this loss of potency, however, because you may accidentally take too much vitamin C. This can cause diarrhea and other health problems.
Adding Vitamin C to Your Diet
Getting your vitamin C from a balanced diet is always the best choice. The recommended intake for vitamin C for males age 19 or more is 75 mg; for women, the DV is 60 mg. You'll find vitamin C in a variety of fruits and vegetables, with the highest concentration being in grapefruit, sweet yellow peppers, kiwi, broccoli, chili peppers and greens, such as kale, parsley and mustard spinach. Some ways to boost your vitamin C intake are:
- Have a bowl of fruit handy for in-between-meal snacking. Mango, kiwi and oranges are all good sources of vitamin C — one cup of mango provides 100 percent of the daily value.
- Eat your fruits and vegetables raw. Since vitamin C is water soluble, it is vulnerable to degradation during processing and cooking. A research paper published by Emerald Insight found that broccoli, spinach and lettuce lost their vitamin C content by 14, 11 and 8.6 percent respectively from steaming, and reduced vitamin C by 54.6, 50.5, and 40.4 percent, respectively from boiling.
- Don't pass on the frozen vegetables. Frozen vegetables often contain higher levels of vitamin C compared with fresh produce, perhaps due to the loss of vitamin C during the storage and transport of fresh produce, reports the New York Times.
- ExRx.net: Vitamin C
- New York Times; The Claim: Always Store Vitamins in the Medicine Cabinet; Anahad O'Connor; Nov. 1, 2010
- Effect of Temperature and Initial Moisture Content on of Vitamin C
- Linus Pauling Institute: Vitamin C
- USDA Dietary Reference Intakes
- USDA National Nutrient Database: Sauerkraut, canned, solids and liquids
- Mango.org: Mango Nutrition
- New York Times:Ask Well: Does Boiling or Baking Vegetables Destroy Their Vitamins?
- Emerald Insight: Effects of different cooking methods on the vitamin C content of selected vegetables