For LOW TESTOSTERONE, research shows that the amino acid L-carnitine encourages testosterone production, improves testicular function, and makes existing testosterone more active. L-carnitine has key roles in energy generation and improving blood flow, with major benefits for men’s health.
Propionyl-L-carnitine is an amino acid that is naturally produced in the body: amino acids are the building blocks that form proteins. This particular amino acid is essential for the delivery of fatty acids to the mitochondria that fuel energy production in each cell. There are several types of carnitine but for male hormone output, propionyl-L-carnitine boosts production of nitric oxide, which directly parallels increasing testosterone levels. Nitric oxide and testosterone are inextricably linked: higher nitric oxide leads to better testosterone synthesis in a man’s testes.
An inevitable consequence of aging is a rapid decline in our cellular energy level. This often manifests as a sense of overall fatigue, depression, and loss of libido. Taking L-carnitine leads to better carnitine levels within tissues. Carnitine is responsible for fueling the fires of energy production at the cellular level, while it also enhances testosterone formation.
We consume small amounts of L-carnitine in our diets by eating meat and fish, but our intake is not enough for a therapeutic effect on male testosterone production. L-carnitine is a water-soluble, vitamin-like molecule structurally. In the body, 75% of L-carnitine is ingested from supplements or the diet, and 25% is synthesized internally from two essential amino acids lysine and methionine. L-carnitine is then stored in skeletal muscles, heart, brain, and testes.
Vegetarians and vegans in particular can benefit from L-carnitine supplements, as can older adults as carnitine levels in the body decline as men age. Researchers compared L-carnitine with testosterone in men who were experiencing erectile dysfunction, low libido, fatigue, and depression. They found that after six months of treatment, L-carnitine was more effective at boosting sexual performance and improving erections than actual testosterone, though the hormone helped somewhat. More importantly, testosterone had the unwanted side effect of causing an increase in prostate volume and size, while L-carnitine did not.1
Low testosterone is defined by the American Urology Association as a level less than 300ng/dL (nanograms of the hormone per deciliter of blood). Low T, as it is commonly known, may affect as many as one-third of men aged 46-89 years. Normal testosterone levels for adult men are between 300 and 950ng/dL, with optimal readings of total testosterone at 500 to 700 ng/dL, and free testosterone at 10 to 13 ng/dL. In men, the decline in testosterone usually begins in their late thirties and decreases at a relatively constant rate of 1 to 3% per year.
L-carnitine can work in a number of ways to encourage optimal testosterone levels:
- It appears to directly stimulate production of testosterone: A recent study showed that serum levels of carnitine were independently associated with free testosterone concentrations in men. Therefore, lower carnitine levels translated into lower testosterone. 2
- L-carnitine relieves depression, and we know that depression can lower testosterone levels. Interestingly, both testosterone and carnitine yielded equal improvements in mood and energy in a 2004 Italian study, although carnitine was more effective in lowering depression scores. Since better moods support higher testosterone levels, this increase in reported well-being cannot be overlooked.1
- Research indicates that L-carnitine can help restore luteinizing hormone, which in men is a hormone that controls testosterone production. Testosterone is made in Leydig cells in the testes, and carnitine exerts a protective effect on the cells of the testes. The function of the testes depends on sexual hormones such as follicle-stimulating hormone (FSH), luteinizing hormone, and testosterone. Studies have found that in subjects with depressed testicular function, supplementation with L-carnitine enhances the recovery of serum sex hormones levels including luteinizing hormone, with resulting benefits to testosterone production, sperm count, and sperm motility.3,7
- L-carnitine improves the number of androgen receptors and their sensitivity to testosterone. Active receptors are necessary to receive and bind testosterone and for the hormone to carry out all of its normal functions.
For testosterone to exert any effect on the body, it must first bind to an androgen receptor inside a cell. The attaching of testosterone to its receptors ‘switches on’ its actions. One significant benefit of carnitine is that it boosts the sensitivity and number of androgen receptors. There might be plenty of testosterone in the blood but without active receptors, the hormone cannot bind to tissues and bring its benefits, and symptoms of testosterone insufficiency may still occur. Studies have shown that taking 2,000mg daily of an L-carnitine supplement can boost male androgen receptors within three weeks.6
- L-carnitine serves as a substantial antioxidant and protects the cell, mitochondrial membrane, and DNA against damage induced by oxygen free radicals. Several studies have been performed to evaluate the antioxidant effect of carnitine: The results indicate that carnitine improves antioxidant enzymes and reduces oxidative stress in the testes and various other tissues.4
L-carnitine supplements may work as effectively as testosterone for male vitality, libido, and to enhance erections, according to an Italian study. Comparing hormone treatment and placebo, 120 patients were divided into randomized groups. Taking carnitine as propionyl-L-carnitine at 2,000 mg/day, and L-carnitine, 2,000 mg/day, improved testosterone-related functions including erectile capacity, modestly exceeding the benefit seen with oral dosing of testosterone itself. Carnitine proved significantly more active than testosterone in improving nocturnal penile tumescence and International Index of Erectile Function score.1
Recommendations: L-carnitine 1,000-2,000 mg per day, with any meals, or as directed by your healthcare provider.
- Cavallini G et al. Carnitine versus androgen administration in the treatment of sexual dysfunction, depressed mood, and fatigue associated with male aging. Urology 2004 Apr; 63(4): 641-46.
- Sakai K, Fukami K, Yamagishi SI, Kaida Y, Adachi T, Ando R, Manabe R, Otsuka A, Sugi K, Ueda S, Okuda S. Evidence for a positive association between serum carnitine and free testosterone levels in uremic men with hemodialysis. Rejuvenation Res. 2013 Mar 14.
- Palmero S, Leone M, Prati M, Costa M, Messeni Leone M, Fugassa E, De Cecco L. The effect of L-acetylcarnitine on some reproductive functions in the oligoasthenospermic rat. Horm Metab Res. 1990 Dec;22(12):622-6.
- Adewoyin M, Ibrahim M, Roszaman R, et al. Male infertility: the effect of natural antioxidants and phytocompounds on seminal oxidative stress. Diseases. 2017;5:E9.
- Bloomer, Richard J., Lesley C. Tschume, and Webb A. Smith. “Glycine propionyl-L-carnitine modulates lipid peroxidation and nitric oxide in human subjects.” International Journal for Vitamin and Nutrition Research 79.3 (2009): 131-141.
- Kreaemer, W. J., et al. (2006) Androgenic responses to resistance exercise: effects of feeding and L-carnitine. Med Sci Sports Exerc., 38:7, 1288 – 1296.
- Rezaei, Nourollah, et al. “Effects of l-Carnitine on the Follicle-Stimulating Hormone, Luteinizing Hormone, Testosterone, and Testicular Tissue Oxidative Stress Levels in Streptozotocin-Induced Diabetic Rats.” Journal of evidence-based integrative medicine 23 (2018): 2515690X18796053.