It seems like every day, some new supplement catches the longevity world’s imagination. And sometimes, a supplement that’s been around for a while will slowly, steadily build up a track record of research that makes the health and longevity world stand up and take notice. That’s the case with acetyl-L-carnitine (ALC), the chemical first cousin of L-carnitine which you’ve probably more likely to have heard of. 

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Both forms of carnitine are intimately bound up in the body’s production of energy inside the cell’s powerplants, the mitochondria. But the alpha form is better absorbed in supplement form and has been found to have more significant effects “above the neck,” on cognitive and mental health especially, so that’s what I’m focusing on here. If you’re interested in your upgrade and possibly extending your healthspan and lifespan (carnitine levels decline with age!), its time to get to know more about this supplement powerhouse that may just keep your mental and physical energy tank powered up all day long. Here’s the topline on this very helpful stuff: 

What’s the difference between acetyl-L-carnitine and L-carnitine?

When it comes to acetyl-L-carnitine and L-carnitine, the first thing to know is that our bodies make both forms, mostly in the liver and the kidneys, by breaking down the amino acids lysine and methionine, key building blocks of protein. And we also get L-carnitine directly, in our diet, mostly from high-protein foods like beef, pork, chicken and dairy. (“Carnitine” is actually derived from the Latin word for meat.) 

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Our cells choose which form they want to make, depending on what the body needs at that moment, but you can’t go wrong with carnitine in any flavor. That’s because it plays such a big role in the body’s fuel system, helping to deliver fatty acids in the bloodstream -- broken down from the fat we consume in our diets -- into the mitochondria where they’re burned for energy. Though people tend to think that sugar/glucose is the body’s primary fuel, when we’re at rest, or not exerting ourselves too vigorously, we actually tend to burn more fat than sugar. That’s a good thing – the less sugar we have to burn, the less insulin we have to produce – and that means protection against prediabetes, metabolic syndrome and type 2 diabetes. Any number of studies have shown reductions in blood sugar in people taking carnitine supplements. And, here’s another bonus: clinical trials that show that ALC supplements can lessen pain and stimulate nerve regrowth in patients suffering from diabetic neuropathy – nerve damage caused by diabetes. 

Can you feel an energy boost with carnitine supplements? 

If you’re basically in good health and already getting an adequate supply of carnitine from the animal protein in your diet, you may feel a slight energy lift, if that, but probably not. However, those on vegetarian diets, and particularly vegans who don’t eat dairy, may well have low blood carnitine levels, and may notice a positive difference after adding a carnitine supplement. Studies suggest that ALC supplements in particular may be effective at helping to countering the fatigue experienced by patients with conditions like chronic fatigue syndrome and possibly multiple sclerosis. And there’s some intriguing evidence that ALC can boost strength and robustness in people becoming frail from simple old age, not necessarily because of some specific disease or condition. In one study, subjects who took 1.5 grams a day of ALC for 10 weeks scored better on a scale that measured frailty and improved grip strength. Certainly something to think about – and potentially very good news – if you’re getting on in years.

ALC to the brain rescue.

One thing to note about the carnitine in ALC supplement form is that it crosses the blood-brain barrier. That’s important. Once inside the brain, the compound may improve function by increasing cellular energy production, as we’ve already talked about. But it also may work directly on neurotransmitters in the brain and reduce levels of oxidative stress (think: free radicals) which is one driver of Alzheimer’s Disease. Not surprisingly, the research on ALC’s ability to push back on mild cognitive impairment and Alzheimer’s is promising, if somewhat mixed. A case in point on the promising side for instance, in one 2018 study, subjects with dementia who took 1,500 mg. of ALC for 28 weeks saw a significant improvement in their cognitive function. 

‍The good news about depression.

Researchers still don’t know exactly how ALC tweaks brain chemistry to improve depression symptoms, they just know that it does. A major review, or “meta-analysis,” of 12 depression/ALC trials that looked at data generated by almost 800 patients, found that supplementation scored improvements in symptoms that were “comparable” to what we see with the standard SSRI anti-depression pharma drugs. And when it comes to side-effects, a nutrient vs something cooked up in the lab – no comparison!  

Two for the price of one.

The body can convert ALC to L-carnitine, and vice versa, such that an ALC supplement can provide the benefits associated with both forms of carnitine. increasing L-carnitine levels, you may be on the receiving end of health benefits that have extensively studied for cardiovascular disease, weight loss and enhanced sports performance. 

Zeroing in on the right amount.

Supplement dosages all over the map – you’ll likely see anything from as little as 500 mg a day all the way up to 3 grams a day being safely consumed. Mild side-effects like heartburn and indigestion are possible, and I usually keep the dose to around 2 grams a day. A number of supplement makers combine ALC with alpha lipoic acid, which is also all to the good, so they’re another option. What’s more, the research suggests that the combo has a particularly good effect on cardiovascular health. 

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There is one yellow flag to consider. Studies have found that L-carnitine supplementation can raise levels of another compound, TMAO, which has been associated with higher levels of cardiovascular disease, this even though most studies have found that carnitine is good for the heart. Particularly if you’re taking a higher dosage of an ALC supplement, you may want to discuss with your doc getting your blood TMAO levels measured and monitored to be sure you keep an eye on them.

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As for red flags, there aren’t a ton of them, but those who are pregnant or breast feeding are likely better off avoiding use, as there’s just not enough information on safety, so always err on the side of caution. Same holds true for children. Those with bipolar disorder should also give ALC a pass as it may worsen symptoms.