Acetyl-L-carnitine (ALCAR) is the acetylated form of L-carnitine — the amino acid derivative that is the essential cofactor for the transport of fatty acids into the mitochondrial matrix for beta-oxidation and that is therefore essential for the generation of ATP from fatty acid oxidation in the heart, the skeletal muscle, and the liver. ALCAR is different from L-carnitine in that it carries an acetyl group (CH3CO-) on the carnitine molecule, which allows it to serve not only as a fatty acid carrier but also as an acetyl group donor for the synthesis of acetylcholine (the primary neurotransmitter of the parasympathetic nervous system and of the neuromuscular junction) and as a buffer for acetyl-CoA in situations where the acetyl-CoA concentration exceeds the capacity of the TCA cycle. These additional functions of ALCAR make it particularly important for the brain, where it serves as a preferred fuel source (the acetyl group is used for the synthesis of acetylcholine and for the support of the TCA cycle in neurons) and for the heart, where it supports the TCA cycle and the beta-oxidation of fatty acids under conditions of metabolic stress.
ALCAR and Cognitive Function
The brain has a high metabolic rate and relies almost exclusively on glucose for its energy needs — it consumes approximately 20% of the total body oxygen consumption despite accounting for only 2% of the body weight. The brain cannot use fatty acids for energy (the blood-brain barrier prevents the entry of long-chain fatty acids into the brain), and it relies on glucose and on the ketone bodies (which are derived from fatty acid oxidation in the liver) as its primary metabolic fuels. ALCAR is one of the few compounds that can cross the blood-brain barrier, and once in the brain, it supports neuronal energy metabolism by donating acetyl groups to the TCA cycle (for energy production) and by synthesising acetylcholine (the neurotransmitter that is essential for memory, for attention, and for the function of the cholinergic neurons of the basal forebrain). The importance of ALCAR for cognitive function is underscored by the observation that ALCAR supplementation improves memory, attention, and mental energy in older adults with age-related cognitive decline, and it is thought to work by supporting the mitochondrial function of the neurons, by reducing the oxidative stress in the brain, and by promoting the synthesis of acetylcholine.
The clinical trials of ALCAR for age-related cognitive decline have shown consistent benefits — a meta-analysis of 12 RCTs in 1,504 older adults with age-related cognitive decline found that ALCAR supplementation significantly improved memory, attention, and mental energy compared to placebo, with an effect size that is comparable to that of the cholinesterase inhibitors (the first-line drugs for the treatment of Alzheimer disease). The mechanism of this cognitive benefit is thought to involve the support of neuronal mitochondrial function (ALCAR helps to maintain the mitochondrial membrane potential and to promote ATP production under conditions of metabolic stress), the reduction of the oxidative damage to neurons (ALCAR reduces the mitochondrial production of ROS and increases the activity of the antioxidant enzymes), and the enhancement of the synthesis of acetylcholine (ALCAR provides the acetyl group for the synthesis of acetylcholine by choline acetyltransferase).
ALCAR and Diabetic Neuropathy
ALCAR has also been extensively studied for its effects on diabetic neuropathy — the peripheral nerve damage that is one of the most common complications of type 1 and type 2 diabetes. The mechanism of diabetic neuropathy involves the oxidative damage to the peripheral nerves that results from the combination of elevated blood glucose, the formation of advanced glycation end-products (AGEs), and the impaired antioxidant defence that is characteristic of diabetes. ALCAR has been shown to improve the symptoms of diabetic neuropathy in multiple RCTs — it reduces pain, burning, numbness, and paraesthesias, and it may also improve the underlying nerve conduction velocity and the nerve fibre density. The mechanism of this benefit involves the support of peripheral nerve mitochondrial function (ALCAR helps to maintain the mitochondrial membrane potential and to reduce the mitochondrial production of ROS in the Schwann cells and the neurons of the peripheral nerves) and the promotion of the repair of the peripheral nerve fibres (ALCAR stimulates the synthesis of the structural proteins and the lipids that are required for the regeneration of the nerve fibres).
Practical Application
For general ALCAR supplementation, the evidence-based dose is 1-3g of acetyl-L-carnitine daily (as a divided dose of 500-1,000mg two or three times daily), taken on an empty stomach for optimal absorption. For age-related cognitive decline and for diabetic neuropathy, the evidence-based dose is 1.5-3g daily, which is the dose that has been used in the majority of the positive clinical trials. ALCAR is generally well-tolerated with no significant adverse effects at doses up to 3g daily, though very high doses may produce gastrointestinal symptoms (nausea, abdominal cramps, diarrhoea) or may cause a fishy body odour (from the trimethylamine that is produced by the gut microbiota from unabsorbed carnitine). For comprehensive cognitive and mitochondrial support, ALCAR pairs well with alpha-lipoic acid (which has complementary effects on mitochondrial function and which is also used for the treatment of diabetic neuropathy), with CoQ10 (which is required for the function of the electron transport chain), with phosphatidylserine (which supports cognitive function through a different mechanism), and with the omega-3 fatty acids (which are required for the structure and the function of the neuronal membranes).
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