左旋肉碱因可以促进脂肪酸氧化代谢，长期以来一直被当成一种减脂补充剂广受追捧。
很高的安全性也是左旋肉碱得以走红的原因之一，正常剂量下，它几乎不会有明显的副作用。2003年，国际肥胖健康组织就已将左旋肉碱认定为最安全的减肥营养补充品。
乙酰左旋肉碱是左旋肉碱的乙酰化形式，这种形式的肉碱在改善认知方面的作用受到人们的关注。
乙酰左旋肉碱可以支持乙酰胆碱的形成，这对于改善阿尔茨海默病患者的症状有重要帮助[4]。
此外，乙酰左旋肉碱还可以通过增加大脑中的能量产生[6]和血液循环[7]，促进神经细胞更有效地交流，这对改善认知能力也是有帮助的。
在与乙酰左旋肉碱的组合配方中，硫辛酸作为“万能的抗氧化剂”和“线粒体能量促进剂”，可以增加能量代谢并保护神经细胞免受糖基化和其他氧化应激的损伤。动物研究和部分临床的数据显示，乙酰左旋肉碱和α-硫辛酸对认知保护具有协同作用[8-11]。
乙酰左旋肉碱可以为大脑提供更多的能量，并能促进对情绪健康至关重要的神经递质，包括乙酰胆碱、γ-氨基丁酸[12]的合成。
研究发现，大多数患者服用一周乙酰左旋肉碱就可以明显改善抑郁症状[14]。对11项临床试验的荟萃分析发现，乙酰左旋肉碱在减轻抑郁症状方面优于安慰剂，具有与标准抗抑郁药相当的效果，并且副作用更少[13]。
补充乙酰左旋肉碱还有助于提高男性功能与生育能力。800多名不育男性参与的9项临床荟萃分析发现，左旋肉碱和乙酰左旋肉碱的组合显著提高了精子的活力，使得成功怀孕的机会增加了4倍以上[15]。
在120名老年患者中，乙酰左旋肉碱和丙酰肉碱的组合（每天2克，持续6个月）提高了男性功能，并且与睾酮替代治疗不同，肉碱不会导致前列腺增生[16]。
患有生育障碍的男性通过补充肉碱，配合辅酶Q10、维生素C、维生素E、维生素B12、叶酸、硒、锌等营养，可以减少氧化应激对精子的损伤，增强精子活性，提高生育能力。
心肌细胞主要依靠脂肪氧化供能，充足的肉碱对心脏健康是非常重要的。慢性心衰患者可以通过补充肉碱、辅酶Q10、肌肽、D-核糖等来促进心脏健康。
乙酰左旋肉碱的其他作用还包括：提高胰岛素敏感性[17-18]；延缓周围神经变性[19]；缓解纤维肌痛[20]等。
·改善认知，每天1500-3000mg
·增加能量和减少疲劳，每天2000mg
·健身和减脂，1000mg运动前后各一次
·减少抑郁症状，每天1000-4000mg
·糖尿病神经病变，每天1500-3000mg
·不育症男性，每天2000-3000mg
[1]Wall BT, Stephens FB, Constantin-Teodosiu D, Marimuthu K, Macdonald IA, Greenhaff PL. Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. J Physiol. 2011 Feb 15;589(Pt 4):963-73.
[2]Malaguarnera M, Gargante MP, Cristaldi E, Colonna V, Messano M, Koverech A, Neri S, Vacante M, Cammalleri L, Motta M. Acetyl L-carnitine (ALC) treatment in elderly patients with fatigue. Arch Gerontol Geriatr. 2008 Mar-Apr;46(2):181-90.
[3]Vermeulen RC, Scholte HR. Exploratory open label, randomized study of acetyl- and propionylcarnitine in chronic fatigue syndrome. Psychosom Med. 2004 Mar-Apr;66(2):276-82.
[4]Montgomery SA, Thal LJ, Amrein R. Meta-analysis of double blind randomized controlled clinical trials of acetyl-L-carnitine versus placebo in the treatment of mild cognitive impairment and mild Alzheimer's disease. Int Clin Psychopharmacol. 2003 Mar;18(2):61-71.
[5]Cuturic M, Abramson RK, Moran RR, Hardin JW. Clinical outcomes and low-dose levocarnitine supplementation in psychiatric inpatients with documented hypocarnitinemia: a retrospective chart review. J Psychiatr Pract. 2010 Jan;16(1):5-14.
[6]Ori C, Freo U, Pizzolato G, Dam M. Effects of acetyl-L-carnitine on regional cerebral glucose metabolism in awake rats. Brain Res. 2002 Oct 4;951(2):330-5.
[7]Volek JS, Judelson DA, Silvestre R, Yamamoto LM, Spiering BA, Hatfield DL, Vingren JL, Quann EE, Anderson JM, Maresh CM, Kraemer WJ. Effects of carnitine supplementation on flow-mediated dilation and vascular inflammatory responses to a high-fat meal in healthy young adults. Am J Cardiol. 2008 Nov 15;102(10):1413-7.
[8]Soczynska JK, Kennedy SH, Chow CS, Woldeyohannes HO, Konarski JZ, McIntyre RS. Acetyl-L-carnitine and alpha-lipoic acid: possible neurotherapeutic agents for mood disorders? Expert Opin Investig Drugs. 2008 Jun;17(6):827-43.
[9]Liu J, Head E, Gharib AM, et al. Memory loss in old rats is associated with brain mitochondrial decay and RNA/DNA oxidation: partial reversal by feeding acetyl-L-carnitine and/or R-alpha -lipoic acid [published correction appears in Proc Natl Acad Sci U S A 2002 May 14;99(10):7184-5]. Proc Natl Acad Sci U S A. 2002;99(4):2356-2361.
[10]Zaitone SA, Abo-Elmatty DM, Shaalan AA. Acetyl-L-carnitine and α-lipoic acid affect rotenone-induced damage in nigral dopaminergic neurons of rat brain, implication for Parkinson's disease therapy. Pharmacol Biochem Behav. 2012 Jan;100(3):347-60.
[11]Hagen TM, Liu J, Lykkesfeldt J, et al. Feeding acetyl-L-carnitine and lipoic acid to old rats significantly improves metabolic function while decreasing oxidative stress [published correction appears in Proc Natl Acad Sci U S A 2002 May 14;99(10):7184]. Proc Natl Acad Sci U S A. 2002;99(4):1870-1875.
[12]Ferreira GC, McKenna MC. L-Carnitine and Acetyl-L-carnitine Roles and Neuroprotection in Developing Brain. Neurochem Res. 2017 Jun;42(6):1661-1675. doi: 10.1007/s11064-017-2288-7. Epub 2017 May 16.
[13]Veronese N, Stubbs B, Solmi M, Ajnakina O, Carvalho AF, Maggi S. Acetyl-L-Carnitine Supplementation and the Treatment of Depressive Symptoms: A Systematic Review and Meta-Analysis. Psychosom Med. 2018 Feb/Mar;80(2):154-159.
[14]Chiechio S, Canonico PL, Grilli M. l-Acetylcarnitine: A Mechanistically Distinctive and Potentially Rapid-Acting Antidepressant Drug. Int J Mol Sci. 2017 Dec 21;19(1):11.
[15]Zhou X, Liu F, Zhai S. Effect of L-carnitine and/or L-acetyl-carnitine in nutrition treatment for male infertility: a systematic review. Asia Pac J Clin Nutr. 2007;16 Suppl 1:383-90.
[16]Cavallini G, Caracciolo S, Vitali G, Modenini F, Biagiotti G. Carnitine versus androgen administration in the treatment of sexual dysfunction, depressed mood, and fatigue associated with male aging. Urology. 2004 Apr;63(4):641-6.
[17]Ruggenenti P, Cattaneo D, Loriga G, Ledda F, Motterlini N, Gherardi G, Orisio S, Remuzzi G. Ameliorating hypertension and insulin resistance in subjects at increased cardiovascular risk: effects of acetyl-L-carnitine therapy. Hypertension. 2009 Sep;54(3):567-74.
[18]Molfino A, Cascino A, Conte C, Ramaccini C, Rossi Fanelli F, Laviano A. Caloric restriction and L-carnitine administration improves insulin sensitivity in patients with impaired glucose metabolism. JPEN J Parenter Enteral Nutr. 2010 May-Jun;34(3):295-9.
[19]Di Stefano G, Di Lionardo A, Galosi E, Truini A, Cruccu G. Acetyl-L-carnitine in painful peripheral neuropathy: a systematic review. J Pain Res. 2019;12:1341-1351.
[20]Rossini M, Di Munno O, Valentini G, Bianchi G, Biasi G, Cacace E, Malesci D, La Montagna G, Viapiana O, Adami S. Double-blind, multicenter trial comparing acetyl l-carnitine with placebo in the treatment of fibromyalgia patients. Clin Exp Rheumatol. 2007 Mar-Apr;25(2):182-8.
[21]Ferrari R, Merli E, Cicchitelli G, Mele D, Fucili A, Ceconi C. Therapeutic effects of L-carnitine and propionyl-L-carnitine on cardiovascular diseases: a review. Ann N Y Acad Sci. 2004 Nov;1033:79-91.
