01Research Directions

L-Carnitine Tartrate research directions

01Research Directions

Why this compound has a literature

L-Carnitine L-tartrate (LCLT) is a salt of L-carnitine with L-tartaric acid, nominally 68% carnitine base and 32% tartaric acid, developed because the free base and hydrochloride are difficult to handle in dry-blend manufacturing. What makes this material unusual from a literature standpoint is that a distinct cluster of trials was conducted using the tartrate salt by name, mostly in resistance-trained populations, while the underlying pharmacokinetic and metabolic evidence relates to L-carnitine as the parent compound. Distinguishing which is which matters when reading claims made about this SKU.

02Literature

What the literature investigates

Trials conducted on the tartrate salt by name

A recognisable group of studies from a single research collaboration used LCLT explicitly. Volek et al. (2002) ran a balanced crossover in ten resistance-trained men taking LCLT equivalent to 2 g carnitine per day for three weeks and reported attenuated exercise-induced increases in plasma markers of purine catabolism and circulating cytosolic proteins after a squat protocol, with MRI-assessed muscle disruption at 41-45% of the placebo area. Kraemer et al. (2003) used the same three-week, 2 g/day design and reported increased IGFBP-3 concentrations before and at 30, 120 and 180 minutes after acute resistance exercise, with no direct effect on absolute concentrations of the other hormones measured. Ho et al. (2010) extended the design to eighteen middle-aged men and women and again reported attenuated purine-metabolism markers. These are small crossover studies (n = 10-18) from a closely related group of investigators, which is a relevant limitation.

Where the evidence is about the parent compound, not the salt

Most of what is known about how carnitine behaves in the body was not generated using the tartrate salt. Evans and Fornasini (2003) reported 5-18% absolute bioavailability for oral doses of 1-6 g against up to 75% for dietary carnitine, and those pharmacokinetic parameters are properties of the carnitine molecule rather than of the counter-ion. Published dosing in the LCLT trials is likewise expressed as grams of carnitine base, not grams of tartrate, so a stated '2 g' in these papers corresponds to roughly 3 g of the 68% salt. No published work located here compares the tartrate salt head-to-head against the hydrochloride or the free base for absorption in humans, so any difference between salt forms should be treated as unestablished rather than as demonstrated in either direction.

Muscle carnitine loading studies that happened to use LCLT

One long-duration study is worth separating out because it used the tartrate salt while asking a different question. Wall et al. (2011), publishing in The Journal of Physiology, gave fourteen healthy men either 80 g carbohydrate alone or 2 g L-carnitine L-tartrate plus 80 g carbohydrate twice daily for twenty-four weeks in a randomised double-blind design, with muscle biopsies at rest and after cycling at 50% and 80% VO2max. Muscle total carnitine rose 21% in the carnitine arm and was unchanged in control; the authors reported 55% lower muscle glycogen use at the lower intensity, higher pyruvate dehydrogenase complex activation and 44% lower muscle lactate at the higher intensity, and an 11% increase in work output from baseline in the performance trial. This was a single study with fourteen participants and a twenty-four-week duration, and the co-ingested carbohydrate load is inseparable from the carnitine in its design.

Tolerability data generated on this specific salt

Because the tartrate counter-ion is part of the ingested material, tolerability data generated on LCLT itself has some standalone value. Rubin et al. (2001) ran a placebo-controlled crossover in ten healthy active men taking 3 g/day of L-carnitine L-tartrate for twenty-one days and reported no statistically significant differences from placebo in a complete chemistry panel, liver and renal function markers, or complete blood count. Kraemer et al. (2006) separately examined LCLT at 2 g carnitine per day for three weeks in ten resistance-trained men and reported upregulated pre-exercise androgen receptor content relative to placebo alongside feeding effects. These are short studies in small samples of healthy young adults; they do not address long-duration intake, other populations, or the TMAO question raised in the wider carnitine literature.

03Specification

What this means when you specify the material

The LCLT trials expressed dose as carnitine base (typically 2-3 g/day of base, i.e. roughly 3-4.4 g of the 68% salt), so a certificate of analysis that reports carnitine content and tartrate content separately is the practical requirement for reconciling a formula against the published protocols. Verify the carnitine assay basis, the L-tartaric acid fraction and the enantiomeric purity, since D-carnitine content is a specification issue independent of the salt form. Tartrate's lower hygroscopicity relative to the hydrochloride is a handling property, not an evidenced biological difference.

04References

Cited literature

Research context only. Each entry describes what a published study examined and reported. These are not claims about this raw material, and not claims about any finished product. Regulatory and labelling judgements belong to the brand placing the product on its market.

In a balanced crossover study in ten resistance-trained men, three weeks of L-carnitine L-tartrate (2 g L-carnitine/day) attenuated exercise-induced increases in plasma markers of purine catabolism and circulating cytosolic proteins after a squat protocol, and MRI-assessed muscle disruption was 41-45% of the placebo area. Volek JS, Kraemer WJ, Rubin MR, Gómez AL, Ratamess NA, Gaynor P. Am J Physiol Endocrinol Metab. 2002;282(2):E474-E482. PMID 11788381 DOI 10.1152/ajpendo.00277.2001
In a balanced crossover placebo-controlled study in ten recreationally weight-trained men, three weeks of L-carnitine L-tartrate (2 g/day) increased IGFBP-3 concentrations before and at 30, 120 and 180 minutes after acute resistance exercise, with no direct effect on the absolute concentrations of the other hormones examined. Kraemer WJ, Volek JS, French DN, et al. J Strength Cond Res. 2003;17(3):455-462. PMID 12930169 DOI 10.1519/1533-4287(2003)017<0455:teolls>2.0.co;2
In a crossover trial in eighteen middle-aged men and women, three weeks of L-carnitine L-tartrate (2 g L-carnitine/day) significantly attenuated biochemical markers of purine metabolism after an acute resistance-exercise challenge. Ho JY, Kraemer WJ, Volek JS, et al. Metabolism. 2010;59(8):1190-1199. PMID 20045157 DOI 10.1016/j.metabol.2009.11.012
In a crossover study in ten resistance-trained men, three weeks of L-carnitine L-tartrate (equivalent to 2 g L-carnitine/day) upregulated pre-exercise androgen receptor content relative to placebo, and post-exercise feeding increased androgen receptor content in both supplement conditions. Kraemer WJ, Spiering BA, Volek JS, et al. Med Sci Sports Exerc. 2006;38(7):1288-1296. PMID 16826026 DOI 10.1249/01.mss.0000227314.85728.35
In a placebo-controlled crossover study, 3 g/day of L-carnitine L-tartrate for 21 days in ten healthy active men produced no statistically significant differences from placebo in a complete chemistry panel, liver and renal function markers, or complete blood count. Rubin MR, Volek JS, Gómez AL, Ratamess NA, French DN, Sharman MJ, Kraemer WJ. J Strength Cond Res. 2001;15(4):486-490. PMID 11726261
In a randomised double-blind study, fourteen healthy men ingested 2 g L-carnitine L-tartrate plus 80 g carbohydrate or 80 g carbohydrate alone twice daily for twenty-four weeks; muscle total carnitine increased 21% in the carnitine arm and was unchanged in control, with 55% lower muscle glycogen use at 50% VO2max, 44% lower muscle lactate at 80% VO2max, and an 11% increase in work output from baseline in the performance trial. Wall BT, Stephens FB, Constantin-Teodosiu D, Marimuthu K, Macdonald IA, Greenhaff PL. J Physiol. 2011;589(Pt 4):963-973. PMID 21224234 DOI 10.1113/jphysiol.2010.201343
A pharmacokinetic review of L-carnitine reported 5-18% absolute bioavailability for oral doses of 1-6 g against up to 75% for dietary L-carnitine; these parameters relate to the carnitine molecule rather than to any particular salt form. Evans AM, Fornasini G. Clin Pharmacokinet. 2003;42(11):941-967. PMID 12908852 DOI 10.2165/00003088-200342110-00002

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