The risk assessment provides companies with a guide for safe upper levels for product formulations, and consumers with vital information on safe dosage levels from products.
Carnitine is an increasingly popular ingredient in dietary supplements intended for weight loss and sports, said the authors of the study, John Hathcock, PhD and Andrew Shao, PhD.
Three different forms of the compound are commonly available: L-carnitine (LCAR), acetyl-L-carnitine (ALCAR), and propionyl-L-carnitine (PLCAR), although the latter is only available in Europe. There is no evidence to suggest that there is any inherent differences between the forms.
The authors applied a safety evaluation method as described in the CRN's Vitamin and Mineral Safety, 2nd Edition which contains the basic features of the US Food and Nutrition Board's risk assessment method, as well as the observed safe limit (OSL) modification adopted as a highest observed intake (HOI) in the FAO/WHO 2006 report.
The absence of any critical effects prevented the expression of the limits as no observed adverse effect levels (NOAEL). Values were presented as OSLs.
A number of human clinical trials were reviewed with carnitine doses ranging from 50 milligrams per day (mg/d) to 6000 mg/d. The latter dose was used in a year-long trial involving 473 patients recovering from a first heart attack, and while no adverse effects were reported at this dose, the database is insufficient to firmly recommend this dose for most adults, said Hathcock and Shao.
Similarly, no adverse effects were observed for a small trial using a dose of 4000 mg/d, but the limited population size and duration are again insufficient as the basis of any recommendation.
"Collectively, the trials at LCAR equivalents of 2064, 2196 or 2000 mg LCAR provide strong evidence that LCAR in this intake range is without adverse effects in patients with a wide variety of unrelated diseases," said Hathcock and Shao.
"From these data, an adult human OSL of 2000 mg of LCAR equivalents is selected," they concluded.
The Council for Responsible Nutrition's (CRN) John Hathcock and Andrew Shao have been busy filling in the risk assessment gaps for a range of nutrients, and the new assessment, published on-line in the journal Regulatory Toxicology and Pharmacology (doi: 10.1016/j.yrtph.2006.06.007), follows Co-Q10, creatine, and lutein and lycopene in the same journal.
More information about the other risk assessments can be found by clicking here.
Hathcock and Shao recently told NutraIngredients-USA.com that another risk assessment, this time for glucosamine and chrondroitin, is expected for publication shortly in the same journal.