Acetyl-L-carnitine (sometimes referred to as ALC or ALCAR) is a popular endurance supplement that plays a key role in energy production through the transportation of fatty acids into the mitochondria for use as fuel during aerobic energy production. It differs from L-carnitine in that it has an acetyl group attached which increases its water solubility and in turn its bioavailability allowing it to pass more freely into the mitochondria and across the blood brain barrier. Acetyl-l-carnitine has become popular with endurance athletes with a number of benefits reported:

Some of the reported benefits of Acetyl-l-carnitine for endurance athletes

  • Muscle glycogen sparing effect
  • Increased ATP levels
  • Reduced reliance on anaerobic ATP production during high intensity exercise
  • Reduced physical and mental fatigue
  • Improved exercise performance
  • Possesses good antioxidant activity
  • Improves antioxidant status
  • Detoxifies ammonia
  • Increased blood flow to the heart and working muscles
  • Improved recovery following exercise
  • Reduced muscle damage and soreness
  • Protects against exercise induced oxidative stress
  • Protects against hypoxic stress

Research looking at Acetyl-l-carnitine

Acetyl-l-carnitine and endurance exercise performance

Research looking at L-carnitine/ALC supplementation and endurance exercise has so far been conflicting with some studies finding improved exercise performance (Panjwani et al., 2007; Kim et al., 2004 – both animal studies;  Cha et al., 2001; Marconi et al., 1985) whilst others have failed to find improved exercise performance (Lee et al., 2007; Broad et al., 2005; Colombani et al., 2001; Greig et al., 1987;). However, most of these studies have looked at short term acetyl-l-carnitine supplementation. In one recent study, researchers looked at the long term supplementation of L-Carnitine (2g/daily of l-carnitine over a 24 week period) and found that this led to significantly increased muscle carnitine content (the first study to demonstrate increased muscle carnitine levels following oral supplementation), increased work output during a 30 minute “all-out” exercise test, preserved muscle glycogen during low intensity exercise and reduced the reliance on anaerobic ATP production during high intensity exercise (Wall et al., 2011). A recent animal study found that rats fed a diet containing 0.5% L-carnitine showed significantly increased time to exhaustion (Pandareesh and Anand, 2013). The researchers observed that supplementation with carnitine led to increased levels of ATP, glycogen, plasma glucose and triglycerides as well as improving the antioxidant status.

Acetyl-l-carnitine and recovery from strenuous exercise

One promising area of carnitine research is the role that L-carnitine supplementation has on recovery from endurance exercise and to reduce mental and physical fatigue.  It’s known that muscle carnitine levels can decrease significantly following endurance exercise (Hiatt et al., 1989) and that supplementing with just 1g of carnitine/daily can help to preserve muscle carnitine levels during intense or prolonged exercise (Giamberardino et al., 1996). A number of studies have demonstrated the potential of carnitine supplementation to improve recovery after strenuous exercise with researchers observing reduced muscle soreness and markers of muscle damage (Karlic and Lohminger, 2004; Kraemer et al., 2003; Volek et al., 2002;). There is also evidence that supplementation with ALC may protect against physical and mental fatigue with researchers observing reduced physical and mental fatigue in hepatitis C patients (Malaguarnera et al., 2011) , chronic fatigue syndrome patients (Vermeulen and Scholte, 2004) and the elderly (Malaguarnera et al., 2008), and reduced fatigue severity in MS patients (Tomassini et al., 2004).

The exact mechanisms by which ALC may improve recovery following strenuous exercise is not completely clear but is likely to be a combination of a number of factors, including: 1) ALC’s antioxidant properties – ALC is known to possess strong antioxidant properties and therefore helps to protect against the oxidative stress during and after intense or prolonged exercise (Huang and Owen, 2012; Síktar et al., 2011; Haorah et al., 2011; Shenk et al., 2009; Ferraresi et al., 2006); 2) ALC’s ability to detoxify waste products like ammonia – a metabolic by-product associated with early fatigue – and reduce both blood and brain ammonia levels (Malaguarnera et al., 2011b; Malaguarnera et al., 2003; Kanter and Williams, 1995); 3) Improved blood flow – supplementation with carnitine can increase blood flow, and therefore enhance oxygen delivery, to the working muscles (Kraemer and Volek, 2000) which may also enhance post exercise recovery; 4) Preservation of plasma testosterone levels – research in animals suggests that acetyl-l-carnitine may help to preserve plasma testosterone levels during periods of chronic stress (Bidzinska et al., 1993).

How to take Acetyl-L-Carnitine?

To aid recovery during periods of intensified training: Most research has generally used 1-2g/daily. It is generally recommended that this is taken on an empty stomach in the morning or early afternoon – try not to take Acetyl-L-Carnitine too late in the evening as it may make you feel more alert and therefore make it harder to sleep.  Higher dosages are unlikely to be beneficial as the excess is likely to be excreted and therefore wasted.  To aid recovery athletes will often take acetyl-l-carnitine during periods of intensified training and then reduce or stop supplementation when training volume is decreased.

For an ergogenic effect: It is important to note that it still not completely clear whether acetyl-l-carnitine has a significant ergogenic effect. The most recent human research that observed an ergogenic effect involved consuming 2g/daily of Carnitine over a longer period (24weeks). Therefore, it appears that if ALC has an ergogenic effect longer term supplementation may be required.

Is acetyl-l-carnitine safe?

Research has found ALC to be safe and well tolerated with only mild side effects. Higher doses (>5-6g daily) may cause diarrhea. Other potential side-effects include a rash and increased appetite.

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