It's cold and flu season, which means many people are reaching for vitamin C, as it may modestly reduce cold symptoms (although it won't prevent a cold). What they may not know is that taking too much vitamin C may also cause stomach upset and diarrhea and, if used long-term, potentially, other negative effects.
To make sure that supplements contain and deliver the amounts of vitamin C listed on their labels, ConsumerLab.com recently tested a variety of vitamin C supplements. Many top-quality products were identified, but two vitamin C supplements were discovered to contain 40 percent more vitamin C than listed, increasing the chance that they could cause side effects in some people. ConsumerLab.com also discovered that one supplement contained 15 percent less vitamin C than listed.
Most adults need only 75 mg to 120 mg of vitamin C per day, which is roughly the amount in a glass of orange juice. Children need just 15 mg to 75 mg. A much higher dose (1,000 mg or more) taken daily throughout the cold season has been shown to reduce the symptoms and duration of a cold, which is why many products are designed to deliver amounts ranging from 250 mg to 1,000 mg per unit. However, side effects may occur when daily intake (including that from foods as well as supplements) exceeds just 400 mg for very young children and 2,000 IU for adults.
ConsumerLab.com also found that a common dose of vitamin C from a high-quality supplement can cost as little as one cent, or over one dollar.
ConsumerLab.com's Vitamin C Supplements Review is available online. It includes quality ratings and comparisons of 25 vitamin C supplements and explains:
- Which vitamin C supplements passed testing, and which failed
- Which high-quality vitamin C supplements are also lowest cost (as low as 1 cent per 500 mg)
- What vitamin C can and cannot do for your health
- The potential advantages of forms of vitamin C, such as Ester-C, sodium ascorbate, and slow-release vitamin C
- The value of additional ingredients, such as bioflavonoids (e.g., quercetin, dihydroquercetin, rutin, and hesperidin), often found in vitamin C supplements
- The vitamin C dosage to help prevent or treat conditions such as colds, gout, and vitamin C deficiency
- The potential side-effects of vitamin C and other concerns, including the potential for kidney stones and interactions with drugs and diagnostic tests
Products in the report include 11 selected by ConsumerLab.com and 14 others that passed ConsumerLab.com's voluntary Quality Certification Program, as well as one other vitamin C supplement similar to one that passed testing. The products included are: Bronson Laboratories Vitamin C Crystals, ChildLife Liquid Vitamin C, CVS Pharmacy C, Douglas Laboratories Ester C Plus, Dynamic Health Laboratories Liquid Vitamin C 1,000 mg, Emergen-C, Ester-C, Finest Nutrition (Walgreen) C Vitamin, Garden of Life RAW Vitamin Code Raw Vitamin C, Gary Null's Suprema C Strawberry, Halls Defense Vitamin C Strawberry, Kirkland Signature (Costco) Vitamin C, Life Extension Vitamin C with Dihydroquercetin, Nature Made VitaMelts Vitamin C, Nature's Plus Animal Parade Vitamin C, Nutrilite Vitamin C Plus, Puritan's Pride C-1000 mg, Rainbow Light Gummy Vitamin C Slices, Rexall Vitamin C, Solgar Ester-C Plus, Spring Valley C, Trader Joe's Chewable Oranges & C, TwinLab C-1000 Caps, Vitacost Vitamin C, Vitafusion Power C, and Vitamin World C-1000 mg.