Labdoor analyzed 29 best-selling vitamin C supplements in the United States for vitamin C content and heavy metal (arsenic, cadmium, lead, mercury) contamination.
The majority of products (17 of 29) recorded vitamin C content within 10% of their label claims, but 10 products deviated off their claims by at least 30%. Products ranged from having 60% less to 116% more than their label claims. The lowest measured vitamin C level fell below the recommended daily allowances (RDAs) of 90 and 75 mg/day for men and women, respectively, needed to protect against vitamin C deficiency. The highest measured vitamin C level exceeded the established Tolerable Upper Intake Level (UL) of 2000 mg/serving for safe vitamin C intake.
All tested products passed heavy metal screens for cadmium, lead, and mercury. 4 products were projected to have inorganic arsenic content in excess of 0.1 mcg/serving. California’s Prop 65 proposes a maximum allowable dose level (MADL) of 0.1 mcg/day for inorganic arsenic, a developmental and reproductive toxin. Flagged inactive ingredients in this batch analysis include aspartame, the artificial sweetener, and 4 artificial coloring agents.
1 in 3 products in our batch analysis recorded vitamin C content that deviated at least 30% off their label claims.
Actual vitamin C content ranged from 60.4% less than their stated label claims to 116.2% more, with products deviating off claims by an average of 25.0%. 1 in 3 products recorded vitamin C levels that were at least 30% more or 30% less than their label claims.
Most of the tested vitamin C products (22 of 29) contained more vitamin C than claimed. On average, these products exceeded label claims by 15.1%. Healthforce Nutritionals Truly Natural Vitamin C had more than 2 times (216.2%) of its label claim. 7 products recorded underages with Pure Radiance Vitamin C performing worst, containing only 39.6% of its claim. Bulk Supplements Vitamin C performed best; its measured vitamin C content matched its label claim exactly.
4 products recorded total arsenic content that, with an assumption of 80% inorganic arsenic contribution, were projected to exceed California’s Prop 65 proposed limit for inorganic arsenic of 0.1 mcg/day.
All products in this report were screened by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for the presence of 4 key heavy metals: arsenic, cadmium, lead, and mercury. In accordance with California’s Proposition 65, the following proposed and established daily intake limits were used to assess heavy metal load and product purity: no more than 0.1mcg/day of inorganic arsenic (proposed), 4.1 mcg/day of cadmium, 0.5 mcg/day of lead, and 0.3 mcg/day of mercury (proposed).
Currently, intake limits for total arsenic have only been established for drinking water. The only available guideline for arsenic in supplement products is a proposed limit from CA Prop 65 on the inorganic component of total arsenic. Generally, inorganic arsenic species (tri- and penta-valent arsenic) are considered more toxic than their organic counterparts. Chemical analysis of this batch of vitamin C products measured arsenic in total. Since research has shown that the contribution of inorganic arsenic to total arsenic is ~80% (in rice), an 80% assumption was used to project and then compare inorganic arsenic content in the vitamin C products to the CA Prop 65 proposed limit of 0.1 mcg/day.
All products passed purity testing for cadmium and mercury. Solgar Ester-C Plus exceeded the Prop 65 lead limit at its maximum recommended dosage of 3 tablets per day. Using 80% of total arsenic measurements per the assumption above, 4 products exceeded the Prop 65 limit for inorganic arsenic.
Liquid, gummy, and chewable vitamin C products generally received lower Nutritional Value scores for having added sugars to enhance palatability.
Most vitamin C supplements in this batch analysis contained minimal caloric loads, fats, carbohydrates, and added sugars.
Liquid, gummy, and chewable vitamin C formulations were generally found to have more calories and added sugars than the traditional tablet products. Rainbow Light Gummy Vitamin C Slices and Nature’s Answer Liquid Vitamin C both recorded 8 g of added sugars and at least 35 calories per serving. Added sugar in 1 serving of these products equates to about a third of the World Health Organization’s proposed limit for added sugars of 25 g per day.
12 of 29 products recorded more than 1000 mg/serving of vitamin C, seen in clinical study to be the lowest level at which a potentially harmful metabolite begins to appear in urine.
Labdoor’s Ingredient Safety calculations are based on penalties for 2 concerns - 1) meeting or exceeding published Tolerable Upper Intake Levels (UL) for the product’s active ingredient, and 2) the presence and severity of added excipients.
Clinical research has found that oxalate, a product of vitamin C metabolism, appears in urine after acute doses of 1000 mg of vitamin C and can increase the risk for kidney stones. 12 of 29 products in Labdoor’s batch analysis recorded vitamin C content greater than 1000 mg/serving. One product, Source Naturals Vitamin C, exceeded the established upper limit for safe vitamin C intake of 2000 mg/day.
The inclusion of controversial additives - artificial sweeteners, coloring agents, and preservatives - was minimal in this category. Only 1 of the tested 29 products, Spring Valley Chewable C, recorded any flagged inactive ingredients. These included the artificial sweetener, aspartame, and 4 artificial coloring agents: Blue 1, Red 40, Yellow 5, and Yellow 6.
29 of 29 tested products recorded vitamin C levels that met the established recommended dietary allowances (RDAs) for adult men and women.
Labdoor calculates Projected Efficacy scores as follows: First, we identify the bioavailability of the active ingredient in question. Then we map where a product’s active ingredient content falls with respect to that ingredient’s pharmacokinetic (PK) profile to estimate its relative efficacy. A PK profile is a quantitative representation of how an administered substance is absorbed, distributed, metabolized, and excreted. PK profiles are specific to the ingredient (vitamin, mineral, protein, etc.) being analyzed and products’ formulations.
Clinical studies show that vitamin C operates on a sigmoidal PK curve. At doses below 30 mg, vitamin C exhibits dose-dependent behavior in which incrementally more vitamin C translates to steadily higher plasma vitamin C concentrations. Between 30 and 100 mg, the same incremental increases in vitamin C doses raises plasma vitamin C concentration exponentially. A dose of 100 mg is the point where some studies suggest that immune cell (neutrophils, monocytes, lymphocytes) saturation is complete, with cells displaying vitamin C concentrations 14 times higher than plasma vitamin C concentrations. Beyond 100 mg doses, the rate of plasma concentration gains slows and plateaus between 70 and 80 umol/L. Gains in plasma concentration are practically absent with vitamin C doses above 400 mg/serving.
In terms of health benefits, the recommended dietary allowances (RDAs) of 90 and 75 mg/day for non-smoking men and women over the age of 19, respectively, protects against diseases related to vitamin C deficiency like scurvy. According to some clinical studies, only at doses of about 500 - 1000 mg/day do additional immune-boosting and antioxidant benefits possibly appear, especially for people at higher risk for atherosclerosis, high blood pressure, pre-eclampsia, arthritis, and age-related macular degeneration.
Research has also shown that regular doses of 250 - 1000 mg of vitamin C does not significantly reduce the incidence of the common cold. “Megadosing”, or taking large amounts Vitamin C at the onset of cold-like symptoms, also does not reduce cold duration or symptom severity more than taking a placebo. It may be possible to shorten the length of a cold by 8% in adults and 14% in children with close to 1000mg of Vitamin C taken regularly each day over at least 3 months.
All but one product, Pure Radiance Vitamin C, met established RDAs and were measured to have vitamin C levels of more than 100 mg/serving. 10 of the 29 products contained between 500 and 1000 mg/serving of vitamin C.