Labdoor analyzed 30 best-selling calcium supplements in the United States, measuring levels of key active ingredients (calcium and vitamin D) as well as heavy metal contaminants (antimony, arsenic, bismuth, cadmium, and silver).
Calcium products fared well in terms of label accuracy, with 20/30 products recording calcium content within 10% of their claims. Calcium supplements are often formulated with vitamin D, which aids in the intestinal absorption of calcium. 24 products claimed vitamin D content, 19 of which exceeded their claims (average variance = +24.7%).
Samples of every calcium supplement passed all six heavy metal assays. Products received reduced Ingredient Safety ratings for the presence of key watchlist ingredients, including artificial coloring agents (FD&C Blue 1, FD&C Blue 2, FD&C Red 40, FD&C Yellow 5, FD&C Yellow 6, and titanium dioxide), artificial sweeteners (sucralose), and controversial preservatives (benzoates).
Actual calcium content ranged from -42.5% to +28.0% vs. the products stated label claims, with the average product exceeding its claim by 3.8%.
In general, product were more likely to record an overage vs. an underge for calcium content, wth 20/30 products exceeding their label claims. Of the 30 products tested in this batch analysis, 20 fell within 10% of their label claims (-10% to +10%). 3 products recorded an average absolute variance of at least 25%; 2 exceeded their label claims by at least 25% while 1 fell below its claim by at least 25%. Tums was the worst offender, falling below its label claim by 43%.
Lab-tested vitamin D content was less precise compared to label claims, ranging from -12.5% to +112.5%. Generally, calcium supplements claiming vitamin D content are more likely to record more vitamin D than claimed, with 79.2% of products claiming vitamin D exceeding their label claims. 8 products recorded vitamin D content within 10% of their claims. Of the 24 products claiming vitamin D content, 15 exceeded their label claims by 10%, 13 products exceeded their claims by 15%, and 8 products exceeded their claims by at least 25%. Only 1 product, Child Life Liquid Calcium/Magnesium, fell below its claim by more than 10%.
All products in this report were screened by Inductively Coupled Plasma (ICP)-based techniques for the presence of heavy metals. Samples of each product passed all six heavy metals assays, indicating that samples contained under 2 PPM (part per million) each of arsenic, lead, cadmium, bismuth, antimony, and silver compounds.
The majority of calcium supplements tested in this batch recorded similar Nutrition Facts panels, with only minimal variation in calorie, fat, carbohydrate, and sugar content.
Both tested gummy-formulated calcium supplements–Vitafusion and Nature Made Calcium Gummies for Adults–recorded 6 g of added sugars and 30 calories per serving, the highest values for these attributes in this category.
Labdoor’s Ingredient Safety calculations are based on two key factors. First, products were penalized when their measured active ingredient values meet or exceed published Tolerable Upper Limits (TUL). Calcium supplements also received reduced Ingredient Safety scores based on the presence and severity of key heavy metals and added excipients.
Four products – Nature’s Bounty Calcium, GNC Calcium Plus, Solgar Calcium, and Citracal Calcium + D3 – recorded calcium quantities at which two servings would either meet or exceed the 2500 mg daily tolerable upper limit (UL) indicated for men and women over 19 years of age. For adults over 51 years of age, the UL is reduced to 2000 mg per day.
Two products – Nature’s Bounty Calcium and Sundown Calcium + D3 – recorded vitamin D quantities at which two servings would exceed the 4000 IU daily UL.
3 of 30 products recorded at least one controversial artificial coloring agent (Blue 1, Blue 2, Red 40, Yellow 5, and/or Yellow 6). 14 products contained titanium dioxide, a whitening agent linked to cancer and Alzheimer’s Disease, primarily in the occupational setting. Other flagged inactive ingredients included the artificial sweetening agent sucralose and the preservative benzoic acid.
Labdoor’s Projected Efficacy calculations are based on two key factors. First, we identified the relative bioavailability of each vitamin and mineral form. Then we compare the measured amounts of each active ingredient form in a sample to established nutrient standard, such as Recommended Dietary Allowances (RDAs) set by the Institute of Medicine (IOM).
Calcium bioavailability, for example, is heavily dependant on supplement formulation. Calcium carbonate is typically the most popular choice for calcium supplements, due in large part to being inexpensive and convenient. Compared to other popular formulations (such as calcium citrate), however, the carbonate form suffers several drawbacks. Dissociation of calcium from carbonate depends on the presence of stomach acids, which requires that supplements containing calcium carbonate be taken with food. Calcium citrate is suggested to be absorbed equally well when taken with and without food. While it has been established that calcium citrate absorption is greater vs. calcium carbonate during fasting states, absorption of each formulation when given with a meal remains a matter of scientific contention. Few studies cite equal bioavailabilities. Some studies estimated that calcium citrate is 2.5 times more bioavailable than calcium carbonate, even when taken with food, the optimal condition for calcium carbonate absorption. Due to its greater bioavailability and lack of dependence on gastric acids, calcium citrate may be beneficial to those suffering from achlorhydria (impaired production of hydrochloric acid), inflammatory bowel disease, or poor gastrointestinal absorption.
Furthermore, calcium absorption depends on the quantity of elemental calcium being ingested.* As a general rule, calcium absorption is inversely correlated to quantity; that is, larger amounts of calcium are expected to be absorbed less efficiently. Studies have suggested that absorption is best when the total elemental calcium content being ingested at one time is less than or equal to 500 milligrams (mg). It is recommended that doses exceeding 500 mg be taken at different times of day. Alternatively, a slow-release formulation may be beneficial in enhancing bioavailability.
The RDA of calcium is set at 1000 mg/day for men 19 - 70 years of age and women 19 - 50 years of age. Women over the age of 50 are recommended to consume 1200 mg of calcium per day. The average product in our batch analysis recorded 701.0 mg of calcium per serving, with total calcium content ranging from 54 mg to 1350 mg per serving. 16 of the 30 tested products recorded calcium carbonate as at least one of their calcium formulations. 9 products recorded the presence of calcium citrate. Other calcium formulations included phosphate, malate, and citrate-malate.
Additionally, calcium supplements are typically fortified with vitamin D, whose primary role is to aid in calcium absorption. 24/30 products recorded vitamin D in their formulations, averaging 820.8 IU per serving. This exceeds the 600 IU RDA indicated for men and women 19 - 70 years of age. All products recording vitamin D contained cholecalciferol (D3) vs. ergocalciferol (D2). Clinical studies have established the inferiority of ergocalciferol to cholecalciferol in improving patient nutrient status, determined by measuring serum 25-hydroxyvitamin D levels.
*Note: Although different formulations have different amounts of elemental calcium (calcium carbonate is 40% calcium by weight while calcium citrate is 21% calcium by weight), the Supplement Facts label typically lists amounts of elemental calcium available.