It has been estimated that 50% of Americans currently take some form of dietary supplement.1–3 Such supplements may include vitamins, amino acids, minerals, fatty acids, and herbs, and they typically are used to maintain or enhance wellness. Similar dietary products also are administered to dogs and cats on the basis of a veterinarian's recommendation or at the owner's discretion. However, the overall percentage of pets receiving dietary products is lower than in humans. A 2006 survey of > 1,100 pet owners in the United States and Australia found that only 10% of owners administer dietary products to their cats and dogs; these products are most commonly multivitamins, chondroprotective agents, and fatty acids.4 Administration of dietary products is more common in some populations of animals, such as those with certain conditions (eg, cancer or heart disease). For example, 31% of dogs with heart disease5 and > 50% of dogs and cats with cancer6 receive dietary products.
Dietary products are accessible for pet owners because they are readily available through over-the-counter purchases at pet stores, pharmacies, and online vendors; products designed specifically for pets as well as supplements designed for human use are administered to pets. However, there is little regulation of these products. In the Dietary Supplement Health and Education Act of 1994, it is indicated that dietary supplements for humans do not require proof of safety or efficacy before marketing. In addition, FDA regulations regarding good manufacturing practices were implemented in 2008 (2009 for small companies). The current regulations can result in an uncertain amount of quality control and raise questions regarding issues of safety, efficacy, appropriate dose, and pharmacologic properties, such as bioavailability and dissolvability.
Inconsistencies in analyzed product content of various glucosamine products for human and veterinary use range from 0% to 221% of the amount claimed on the label.7,8 The range of actual bacterial concentrations in probiotics in 1 study9 was 0% to 215% of the label claim. In addition, the organisms in most dietary products were improperly identified or sometimes were not detectable.9,10 Clearly, the lack of product regulation for human dietary supplements and similar veterinary dietary products allows the possibility of inefficacy contamination, or other undesirable effects.
Taurine and carnitine play an important role in cardiac function, and supplementation to correct deficiencies or to provide pharmacologic effects has been recommended.11–18 Consequently taurine and carnitine are 2 of the more commonly used dietary products in dogs and cats with cardiac disease. In a study5 of dogs with cardiac disease, carnitine and taurine were the third and fourth most commonly administered dietary products, respectively, with 7% of dogs receiving carnitine and 6% of dogs receiving taurine. In a study19 in cats, carnitine was the second most commonly administered dietary product. In certain populations (eg, breeds of dogs with dilated cardiomyopathy that appear to be predisposed to taurine or carnitine deficiency or cats with dilated cardiomyopathy), it is likely that the frequency of administration of taurine or carnitine is even higher.
The full potential for supplementation of taurine and carnitine in animals with cardiac disease or other medical conditions is not yet known; however, when these compounds are administered, it is important that a good-quality product be used to achieve potential benefits and to reduce the risk for toxic effects. Therefore, the overall purpose of the study reported here was to test the quality of representative commercial taurine and carnitine products. Specifically, the 4 objectives of the study were to determine the amount of taurine or carnitine contained in the product as compared with the amounts in the label claim; to test whether the products contained the representative contaminants mercury, arsenic, or selenium; to evaluate whether product labels conformed to federal guidelines; and to determine the disintegration properties of the products.
Materials and Methods
Eleven taurinea-k and 10 L-carnitinel-u products were selected from Internet and in-store searches of common and readily available brands. Twenty of the 21 products were human dietary supplements, while 1 was a similar product sold for use in animals. All products except onek were purchased from Internet vendors, and a single lot of that product was obtained from our veterinary hospital pharmacy. For 2 taurine products,f,k 2 lots of each product were obtained from different companies to test variability between lots. Product labels were examined to determine conformity with FDA guidelines for general information (eg, name of product, net quantity, manufacturer, and directions for use), product facts, and health or structure-function claims.20 After label evaluation, samples were transferred to unmarked bottles and a code was assigned to each so that investigators remained unaware of the identity of each product. To determine the amount of taurine or carnitine contained in a product, 30 to 50 tablets or capsules of each product were submitted for taurine, carnitine, and mineral analysis.
Samples were submitted to the Amino Acid Laboratory at the University of California, Davis, for taurine analysis. A composite sample of 10 randomly selected tablets or capsules was analyzed, and the result was reported as the mean amount per tablet or capsule for that product. Samples were homogenized,v and 125 mg of homogenized sample was extracted with 6% sulfo-salycylic acid. The supernatant was diluted with lithium citrate loading bufferw (0.2 mol/L), adjusted to pH 2.2, and filtered (0.45-μm filter)x prior to analysis. Samples were loaded onto an automated amino acid analyzery and analyzed by use of cation-exchange, high-performance liquid chromatography and ninhydrin-reactive colorimetric detection. Taurine standardsz were also analyzed by use of the same procedures. All samples were analyzed in duplicate.
Samples for L-carnitine analysis were submitted to a commercial laboratoryaa Two tablets or capsules of each product were randomly selected, and aqueous preparations were made of each. Each aqueous preparation was tested in triplicate, and the mean of the duplicate preparations was calculated. The L-carnitine analysis was performed by use of a radioenzymatic technique in which L-carnitine reacted with excess 14C-labeled acetyl coenzyme A in the presence of carnitine acetyl transferase to generate a directly proportional amount of 14C-labeled acetyl carnitine.21 Residual labeled acetyl coenzyme A was removed, and the labeled acetyl carnitine end product was counted on a liquid scintillation analyzer.bb The L-carnitine standardscc were also analyzed by use of the same procedures.
To determine the amount of mercury, arsenic, or selenium in the products, a composite sample of 10 randomly selected tablets or capsules from each taurine and carnitine product was analyzed. Samples were homogenizedv and then digested by use of a modification of an existing technique.22 Each 0.5-g sample was digested for 24 hours in 5 mL of 16M nitric acid.dd Tubes were then placed in a 50°C water bath for 3 hours, after which time 6N HClee was added to achieve a volume of 75 mL. The solution was mixed well and allowed to sit for at least 12 hours. The supernatant was removed and analyzed by use of a transversely heated graphite atomizer technique coupled with a flow injection analysis system on an atomic absorption spectrophotometer.ff Arsenic,gg mercuryhh and seleniumii standards were also assayed by use of the same procedures. All samples were assayed in duplicate. Samples containing insubstantial amounts (< 1 mg/kg of product) of mercury, arsenic, or selenium were considered uncontaminated.
To test disintegration properties of the tablet forms of the dietary products, we used the procedures in a protocol for a home disintegration test, with modifications to improve consistency23 Briefly, 118 mL of white vinegar was heated in a 250-mL Erlenmeyer flask in a shakerjj set at a stir rate of 120 revolutions/min. Once the vinegar reached 37°C, a tablet was placed in the container, which was then maintained at a constant temperature of 37°C. The time at which the tablet was observed to no longer be in its original tablet form was recorded (up to a maximum of 45 minutes). Tests were performed in duplicate for each taurine and carnitine product.
Data were calculated as the median and range. For evaluation of taurine and carnitine content, results for our laboratory analysis were compared with amounts listed in the label claim, and the percentage difference (higher than or less than the label claim) was calculated. Data were analyzed by use of commercially available statistical software.kk
Results
For taurine analysis, 10 of 11 products were within 10% of the stated label claim, and 3 of 11 were within 5% of the label claim (Table 1). The percentage difference in taurine content between our laboratory analysis and the label claim ranged from −26.3% to 2.5% (median, −5.7%). For the 2 products obtained from each of 2 companies (ie, 2 separate lots of each product were analyzed), the percentage differences for each of the 2 lots were −4.0% and 1.3% and −5.9% and −1.9%, respectively. Most products contained less taurine than the label claim.
Results of analysis of 11 commercially available taurine dietary products.
| Product | Form | Content (mg)* | Difference (%)‡ | Disintegration time (min)† | ||
|---|---|---|---|---|---|---|
| Label claim | Laboratory analysis | Test 1 | Test 2 | |||
| A | Capsule | 1,000 | 737 | −26.3 | — | — |
| B | Capsule | 500 | 465 | −7.1 | — | — |
| C | Capsule | 1,000 | 1,025 | 2.5 | — | — |
| D | Capsule | 500 | 477 | −4.5 | — | — |
| E | Capsule | 500 | 465 | −7.1 | — | — |
| F-1§ | Capsule | 500 | 480 | −4.0 | — | — |
| F-2§ | Capsule | 500 | 507 | 1.3 | — | — |
| G | Tablet | 500 | 469 | −6.2 | 7.5 | 8.0 |
| H | Tablet | 500 | 467 | −6.6 | 27.3 | DND |
| I | Tablet | 500 | 473 | −5.4 | 1.7 | 2.7 |
| J | Tablet | 500 | 461 | −7.8 | 34.5 | 36.6 |
| K-1§ | Tablet | 250 | 235 | −5.9 | 26.0 | 25.0 |
| K-2§ | Tablet | 250 | 245 | −1.9 | 26.0 | 30.0 |
Represents the amount of taurine contained in each tablet or capsule.
Number of minutes for a tablet to disintegrate in white vinegar at 37°C; disintegration was defined as the tablet was observed to no longer be in its original tablet form.
Represents the percentage difference between the amount in the label claim and results of the laboratory analysis of the product.
For this product, a sample from each of 2 lots was analyzed.
— = Not applicable. DND = Did not disintegrate within 45 minutes.
All carnitine products were within 10% of the label claim, and 6 of 10 were within 5% (Table 2). Median percentage difference for carnitine products was 3.6% (range, −2.6% to 8.8%). Three products contained less carnitine than the label claim, whereas 7 products contained more.
Results of analysis of 10 commercially available carnitine dietary products.
| Product | Form | Content (mg)* | Difference (%)‡ | Disintegration time (min)† | ||
|---|---|---|---|---|---|---|
| Label claim | Laboratory analysis | Test 1 | Test 2 | |||
| L | Capsule | 500 | 494 | −1.2 | — | — |
| M | Capsule | 500 | 527 | 5.3 | — | — |
| N | Tablet | 500 | 520 | 4.0 | 26.0 | 23.5 |
| 0 | Tablet | 500 | 537 | 7.5 | DND | 31.5 |
| P | Tablet | 500 | 544 | 8.8 | DND | DND |
| Q | Tablet | 500 | 544 | 8.8 | DND | DND |
| R | Tablet | 500 | 508 | 1.6 | DND | DND |
| S | Tablet | 500 | 487 | −2.6 | 21.8 | 34.5 |
| T | Tablet | 500 | 516 | 3.3 | DND | DND |
| U | Tablet | 500 | 490 | −1.9 | 32.5 | 37.0 |
Represents the amount of carnitine contained in each tablet or capsule.
See Table 1 for remainder of key.
No substantial amounts of mercury, arsenic, or selenium were found in any of the taurine or carnitine samples (results for all analyses were < 1 mg/kg of product). Only 3 taurine samples contained detectable concentrations of selenium (2 lots of 1 productk and 1 sample of a second producta). For these 3 taurine samples, the selenium content was 270, 290, and 240 ng/g, respectively The same 2 lots of 1 taurine product in which low concentrations of selenium were detected also contained arsenic at concentrations of 8.2 and 8.7 ng/g, respectively All product labels conformed with FDA guidelines.20
For disintegration testing of taurine tablets, only 1 of the 5 products did not disintegrate within the 45-minute test period in 1 of the 2 tests (Table 1). For the other 4 taurine products (including 2 lots for 1 product), the median time to disintegration was 26 minutes (range, 1.7 to 36.6 minutes). For carnitine tablets, 5 of the 8 products tested did not disintegrate during the 45-minute period in at least 1 of the 2 tests performed on each product (Table 2). In addition, 4 did not disintegrate during either test, and 1 disintegrated in only 1 of the 2 tests. Median time to disintegration for the carnitine tablets was 29.3 minutes (range, 21.8 to 37.0 minutes).
Discussion
The lack of regulation has important implications for the administration of dietary supplements in humans and similar products in domestic animals. Variability was found in amounts of actual ingredient, compared with amounts listed in the label claims, for taurine and carnitine products in the study reported here. However, the ranges were less than those in similar studies,7–9 with almost all products within 10% of the stated amount. Although products that contain less than the amount in the label claim may have reduced efficacy because actual administered doses would be less than expected, products with concentrations higher than the label claim could raise safety concerns. Taurine and carnitine are unlikely to pose a threat for toxic effects because of their wide margin of safety, but other dietary compounds could be dangerous when given at inadvertently high doses. Assessment of blood and plasma taurine concentrations can be used to assess appropriate blood concentrations.
Analysis of the disintegration tests revealed that there was a great deal of variability among products and even among tablets within the same product. However, it must be mentioned that an in vitro study does not completely recreate the in vivo dissolution of tablets, and additional studies would be needed to more accurately test in vivo properties. In the study reported here, tablets were tested for disintegration as defined by the lack of a cohesive form, not the actual dissolution of the material in solution, which is more indicative of effective absorption and utilization. For many of the tablets tested in this study, the contents did not dissolve and were still evident at the bottom of the beaker at the end of each test. Therefore, this study did not address the bioavailability of the tablets. Additional studies would be necessary to determine bioavailability as well as the reason or reasons for the high variability in disintegration time, even between tablets of the same product. In addition, a limit of 45 minutes was allotted for each disintegration test, which may not accurately resemble in vivo conditions. For example, total gastrointestinal transit time ranges from 23 to 55 hours in dogs and 26 to 35 hours in cats, depending on breed, age, stomach contents, and other factors.24–26 Finally, dissolution testing was not performed in accordance with the more rigorous US Pharmacopeia standards on disintegration and dissolution of nutritional supplements.27 Therefore, our tests served mainly to characterize the high variability in disintegration behavior among products for an in vitro test condition.
Product labels were in compliance with FDA guidelines. This is in contrast to results in other studies,9,10 in which investigators have found violations in human and veterinary products, including listing of organisms that were not included in commercial probiotics, misidentification of organisms, and spelling errors. Labeling compliance may have been better in the study reported here because of increased public demand in recent years, the compounds (ie, taurine and carnitine) evaluated, or the specific products tested.
Undetectable or extremely low concentrations of arsenic, selenium, and mercury were found in all samples tested. The 2 highest selenium concentrations were in 2 lots of a single taurine product (270 and 290 ng/g, respectively). It is unlikely that these amounts would cause clinical problems, even with prolonged administration of the product. In humans, doses of 1 mg/d from supplements have acute toxic and mutagenic properties.28 Dogs and rats developed signs of chronic selenium toxicosis when administered a dietary concentration of 5 to 15 μg/g,28 compared with the Association of American Feed Control Officials' Dog Food Nutrient Profile minimum for selenium of 0.11 μg/g with a maximum of 2 μg/g.29
A limitation of our study was that only a subset of all products available commercially was analyzed. Common products were selected that are readily available to consumers; thus, this study does not extend to all products available. Additional studies would be needed to complete a comprehensive survey of all taurine and carnitine dietary supplements available for humans and similar products commercially available for domestic animals, and it is not clear whether those products would yield similar results. In addition, the only contaminants that we evaluated were arsenic, mercury, and selenium. This does not provide a complete composition analysis of the products, and a more thorough examination of other possible contaminants (such as zinc or iron) would be useful. Another limitation is that the handling of products during storage and shipping before we received them could not be controlled; however, we believe that the conditions described here represent the situations faced by consumers who purchase these products in stores or from online vendors.
Because of the lack of regulation and widespread variation in quality control, it is imperative that veterinarians specifically check the quality of human dietary supplements and similar dietary products formulated for domestic animals before recommending their administration to patients. In addition, clinicians must be aware that owners may administer these products without the knowledge of their veterinarian. Therefore, asking owners specifically about human dietary supplements and similar products for domestic animals and educating them about potential concerns (eg, dose, efficacy, toxic effects, and quality) is important for optimal patient care. One Web site30 can serve as a source for information on independent testing of quality control of dietary products, which can enable consumers to evaluate specific commercially available products and gather information on the reliability of those products. The US Pharmacopeia Dietary Supplement Verification Program31 also provides independent evaluation of dietary supplements. Currently, the USDA (in conjunction with other government agencies) is developing a dietary supplement ingredient database, which will list reliable estimates of content for popular supplements.32 In addition, the FDA issued a final ruling in 2007 regarding quality-control practices for human dietary supplements to help ensure that manufacturers uphold quality production methods and that products are free from contaminates and are accurately labeled.33 Although there is a trend toward recognition of the lack of regulation for human dietary supplements and similar products formulated for domestic animals, many additional changes need to be made to ensure products available to consumers are as marketed and that labels are trustworthy indications of content.
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Taurine 1000, Jarrow Formulas, Los Angeles, Calif.
Taurine, Solgar Vitamin and Herb, Leonia, NJ.
Mega taurine caps, Twinlab, Ideasphere, American Fork, Utah.
Taurine, Swanson Health Products, Fargo, ND.
Taurine, Vitamin Shoppe, North Bergen, NJ.
Taurine, NOW Foods, Bloomingdale, 111.
Taurine caps, Country Life, Hauppauge, NY.
Taurine, Puritan's Pride Inc, Oakdale, NY.
Taurine 500, General Nutrition Corp, Pittsburgh, Pa.
Taurine, Vitamin World, Ronkonkoma, NY.
Taurine tablets, PetAg Inc, Hampshire, 111.
L-carnitine 500, Jarrow Formulas, Los Angeles, Calif.
L-carnitine caps, Country Life, Hauppauge, NY.
Maxi L-carnitine, Solgar Vitamin and Herb, Leonia, NJ.
L-carnitine, NOW Foods, Bloomingdale, 111.
Mega L-carnitine, Twinlab, Ideasphere, American Fork, Utah.
L-carnitine, Swanson Health Products, Fargo, ND.
CarniPure L-carnitine, Vitamin Shoppe, North Bergen, NJ.
L-carnitine, Puritan's Pride Inc, Oakdale, NY.
L-carnitine, General Nutrition Corp, Pittsburgh, Pa.
Heart Healthy L-carnitine, Vitamin World, Ronkonkoma, NY.
Polytron, Brinkman Instruments, Westbury NY.
Lithium citrate loading buffer, Biochrom Ltd, Cambridge, England.
Millex—FH, Millipore, Billerica, Mass.
Biochrom 30, Cambridge, England.
T-0625, Lot 58F0300, Sigma-Aldrich Co, St Louis, Mo.
Metabolic Analysis Labs, Madison, Wis.
Packard/Perkin-Elmer Life Sciences, Waltham, Mass.
L-carnitine inner salt, C-0158, Lot 094K0821, Sigma-Aldrich Co, St Louis, Mo.
Trace metal grade, A509-212, Fisher Scientific, Pittsburgh, Pa.
A144s-212, Fisher Scientific, Pittsburgh, Pa.
AAnalyst 800, Perkin-Elmer, Norwalk, Conn.
Spex CertiPrep, PLAS2-2Y, Fisher Scientific, Pittsburgh, Pa.
Spex CertiPrep, PLHG2-1AY, Fisher Scientific, Pittsburgh, Pa.
Spex CertiPrep PLSE2-2Y, Fisher Scientific, Pittsburgh, Pa.
Queue Orbital Shaker, Queue Systems, Parkersburg, Wva.
Systat, version 11.0, SPSS Inc, Chicago, Ill.
