Do Vitamin C Supplements Go Bad or Lose Potency?

Vitamin C supplements are generally considered safe for most people when you stick to a reasonable dosage, according to the National Institutes of Health (NIH). But if you hang onto them too long, these supplements can break down, 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.

Here's what you should know about vitamin C's shelf life and the risks of taking expired vitamin C.

Some vitamin C supplements may not have an expiration date on the bottle. That's because the Food & Drug Administration does not require manufacturers to include this kind of date on their packaging (the same goes for other vitamins, like multivitamins that contain vitamin C and products like Emergen-C). More often, you might see a "use by" or "best before" date on the label.

While vitamin C is likely not dangerous to take after its "use by" date, it almost certainly will have lost potency. One April 2019 study in the ​Brazilian Journal of Pharmaceutical Sciences​ found 92 percent of vitamin C supplements have significant losses in concentration amounts after 12 months of storage.

In other words, it's not necessarily bad to take expired vitamin C (unless it has other ingredients that pose a risk once they've broken down), but you're probably not going to get the full amount of the nutrient listed on the bottle.

Storage temperature and sunlight exposure can both affect vitamin C's shelf life. Indeed, an October 2016 study in the ​International Journal of Applied Pharmaceutics​ found that under refrigeration, vitamin C has a lower rate of degradation compared to room temperature.

Humidity comes into play, too. An older but still relevant March 2010 study in the ​Journal of Agricultural and Food Chemistry​ found that vitamin C supplements showed signs of breaking down above 80 percent humidity, which is about the level produced by the steam from a hot shower.

Translation: To extend the shelf life of your vitamin C, it may be best to store it in the fridge or at least a cool, dry and dark place rather than in the bathroom medicine cabinet.

The initial quality of the supplement may affect its breakdown process as well. Higher-quality supplements packaged with very little moisture tend to break down more slowly than lower-quality supplements, according to a January 2015 study in the ​International Journal of Food Properties​. 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.

To find a high-quality supplement, look for one that has been third-party tested by an independent laboratory. The most common third-party testers are USP, Consumer Lab, NSF and NSF for Sport.

Not all vitamin C supplements have printed expiration dates, and you can still take old vitamin C tablets. However, especially 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, nausea, stomach cramps and other health problems, according to the NIH.

If you are concerned about the level of vitamin C in expired tablets, then you may wish to look into other uses for expired vitamin C tablets. It is possible to dissolve vitamin C tablets to use on your face in lotions and masks.

Because vitamin C is an antioxidant and anti-inflammatory, as well as a stimulator for producing collagen, using it on your skin could be beneficial, according to the Linus Pauling Institute. The topical use of vitamin C may also help prevent and treat ultraviolet-induced photodamage (from exposure to the sun or tanning beds).

Dissolving twenty 500-milligram tablets in 100 milliliters (about 3 ounces) of distilled water will create a 10 percent concentration of vitamin C. The Linus Pauling Institute recommends a maximum of 20 percent vitamin C solution for use on the skin, and a 10 percent solution will not cause any adverse effects.

You can use your homemade vitamin C solution by dipping a cotton ball into your mixture and dabbing it on your face and neck. This product does not need to be rinsed off and will absorb into your skin.

Getting your vitamin C from a balanced diet is always the best choice. The recommended daily intake for vitamin C is between 75 and 90 milligrams, according to the NIH.

Good sources of vitamin C include 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 include:

• ​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 60 milligrams, per the USDA.
• ​Eat raw or steamed vegetables.​ Different cooking methods can change the nutrient content of your vitamin-C-rich veggies. Steaming is considered the best cooking method to preserve the vitamin C in vegetables, according to a September 2013 study in ​​Nutrition & Food Science​​.
• ​Don't pass on the frozen veggies.​ Frozen vegetables often contain just as much vitamin C as fresh produce, according to a June 2017 study in the ​Journal of Food Composition and Analysis​.