Labdoor analyzed 28 best-selling zinc supplements in the United States for elemental zinc content and heavy metal (arsenic, lead, bismuth, cadmium, silver, antimony) contamination.
Products performed fairly well in label accuracy. More than two-thirds of the tested products were found to have actual amounts of elemental zinc within 5% of their label claims. 24 of 28 products contained more elemental zinc than claimed, averaging an excess of 4.7%. Elemental zinc content ranged from 2.3 mg to 59.9 mg per serving. 25 of 28 products, in one serving, met or exceeded the Recommended Dietary Allowances (RDAs) of 11 mg and 8 mg of zinc per day for men and nonpregnant women ages 19+, respectively.
12 of 28 products exceeded zinc’s Tolerable Upper Intake Level (UL) of 40 mg per day for healthy men and women ages 19+ in one serving. All products passed heavy metal screens for arsenic, lead, bismuth, cadmium, silver, and antimony, indicating that 2 PPM or more of each heavy metal was not detected. Flagged inactive ingredients were only noted in 1 product, Trace Minerals Ionic Zinc, which contained a benzoate-based preservative with cancer-causing potential.
Collective data for this analysis relied on the analytical chemistry method, ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry), to detect and quantify elemental zinc content and heavy metal (arsenic, lead, bismuth, cadmium, silver, antimony) load.
Products generally performed well in label accuracy, with 21 of 28 products recording elemental zinc levels within 5% of their label claims.
27 of 28 products recorded Label Accuracy scores above 9 (out of 10). Measured elemental zinc deviated from label claims by an average of 4.4%. 21 of 28 products recorded zinc levels within 5% of their label claims.
All but 6 products measured more elemental zinc than claimed. On average, these products exceeded label claims by 4.7%. New Chapter Zinc exceeded its label claim most with 11.3% more zinc than claimed. Solaray Zinc fell below its label claim most with 9.8% less zinc than claimed. Solgar Zinc performed best: its measured zinc content was only 0.2% less than its label claim.
All 28 products passed heavy metal screens for arsenic, lead, bismuth, cadmium, silver, and antimony (less than 2 PPM each).
All products in this report were screened by ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry) for the presence of 6 key heavy metals: arsenic, lead, bismuth, cadmium, silver, and antimony. The ICP-OES method is limited to detecting concentrations of heavy metals no less than 2 PPM (parts per million). All of the tested products passed screens for the 6 heavy metals, indicating that the products contained less than 2 PPM of each metal.
Products performed fairly well in terms of unnecessary fat, carbohydrate, and sugar content, recording an average of 9.99 (out of 10) in Nutritional Value scores.
Zinc products in this batch recorded similar nutritional value scores, with only minimal variation in calorie, fat, carbohydrate, and sugar content. The 3 lozenge-formulated products tested recorded additional carbohydrates and/or sugars. Source Naturals Wellness Zinc Lozenges contained the most sugar with 2 g of sugar and 10 calories per serving.
12 of 28 products exceeded zinc’s Tolerable Upper Intake Limit (UL) for healthy men and women ages 19+ of 40 mg per day in one serving.
The NIH cites the following ULs for zinc per day: 12 mg (ages 4-8), 23 mg (ages 9-13), 34 mg (ages 14-18), and 40 mg (ages 19+). These values apply to both males and females in their respective age groups. For adults above 19 years of age, research shows that bulk doses of zinc as low as 50 mg per day can cause headaches, loss of appetite, nausea, abdominal cramps, and diarrhea. Chronic intake of zinc above the ULs has been associated with increased risks for copper and/or iron deficiency, impaired immune responses, reduced levels of high-density lipoproteins (HDL cholesterol), and harmful changes to urinary physiology. Dosages above the ULs are sometimes prescribed for specific health conditions, but should only be taken under the guidance of a licensed physician.
Adult zinc supplements are not always appropriate for children. 12 of 28 products recorded elemental zinc content above 40 mg per serving, the UL for men and women ages 19+. Bulk Supplements Zinc Gluconate measured the highest zinc content with 59.9 mg of zinc per serving. 13 products measured levels of zinc in one serving that exceed the UL of 34 mg per day for ages 14-18. Of the 3 lozenge formulations, only Nature’s Plus Animal Parade Kid Zinc Lozenges measured elemental zinc content less than 12 mg per serving, the UL for children ages 4-8.
Labdoor penalizes products for having flagged inactive ingredients in their formulations, including artificial sweeteners, artificial coloring agents, and potentially harmful preservatives. Only 1 product in this batch analysis recorded any of these items. Trace Minerals Ionic Zinc was found to contain potassium benzoate, a benzoate-based preservative with cancer-causing potential.
All but 4 products measured at least 11 mg of elemental zinc per serving, meeting the RDAs for men and nonpregnant women ages 19+ of 11 mg and 8 mg of zinc per day, respectively.
In clinical study, amino acid chelates like zinc monomethionine demonstrate a higher bioavailability than inorganic compounds like zinc oxide. The bioavailabilities of zinc gluconate, zinc acetate, and zinc citrate fall somewhere in between. In a small clinical trial of 15 subjects, findings suggest that zinc picolinate may be better absorbed than zinc citrate or zinc gluconate. 13 products in this analysis used zinc gluconate in their formulations, 6 products used zinc monomethionine or other amino acid chelates, 3 products used zinc picolinate, and 1 product used zinc oxide.
The NIH cites the following Recommended Dietary Allowances (RDAs) for zinc per day: 5 mg (ages 4-8), 8 mg (ages 9-13), 11 mg (males ages 14+), 9 mg (females ages 14-18), and 8 mg (nonpregnant females ages 19+). All but 4 products measured at least 11 mg of elemental zinc per serving, meeting the RDAs for males and nonpregnant females ages 19+. Elemental zinc content ranged from 2.3 mg per serving in Biotics Research Aqueous Zinc to 59.9 mg per serving in Bulk Supplements Zinc Gluconate. Research has also found that zinc absorption incrementally increases with higher doses until doses of ~20 mg, at which further increasing doses produces relatively small and progressively diminishing increases in zinc absorption in healthy adults. 20 of 29 products measured more than 20 mg of elemental zinc per serving.
Zinc plays a critical role in immune function, wound healing, protein and DNA synthesis, and other developmental processes. Despite some conflicting evidence, research generally suggests that supplemental zinc may be beneficial for the common cold. Recently, a systematic review published in the Cochrane Library concluded that zinc (as lozenges or syrup) can reduce the duration and severity of the common cold in healthy people, when taken within 24 hours of the onset of symptoms. However, the dosage for this indication has yet to be established.
Zinc has also been prescribed by doctors to treat acute childhood diarrhea due to zinc deficiency and skin diseases like acne vulgaris and acrodermatitis. Research also suggests that zinc supplements may help slow the progression of age-related macular degeneration in patients with advanced eye disease, but only when taken in combination with antioxidants, including vitamin C, vitamin E, and beta-carotene.