L-carnitine has been advertised as a fat-lowering and performance-enhancing supplement, although scientific evidence for its effectiveness is lacking. The uptake of about 1–2 g of L-carnitine per day may result in the formation of metabolites like trimethylamine-N-oxide (TMAO), which in turn may be converted to potential carcinogens or promote the development of cardiovascular diseases.Methods and results:
To assess whether an L-carnitine supplementation changes overall metabolism or causes the formation of previously unknown metabolites, we analyzed plasma samples from Fischer 344 rats originating from a previous study 2 using a multi-platform metabolomics approach comprising LC-MS/MS and GC×GC-MS methods. Despite an intake of up to 352 mg L-carnitine/kg body weight/day for 1 year, plasma concentrations of only 29 out of 359 metabolites were significantly influenced, the induced concentration changes being often comparatively small. Nevertheless, a clear dose-response relationship and a substantial concentration increase were observed for TMAO, i.e. a tenfold higher TMAO level was measured in the high-dose group when compared to the control (2.5 versus 25.0 μM).Conclusion:
Although L-carnitine supplementation did not cause large changes in the plasma metabolome, a higher risk for cardiovascular disease due to chronically elevated TMAO plasma concentrations cannot be excluded.