Alpha lipoic acid (ALA) is a sulfur-containing compound your body produces naturally to help convert food into energy. It functions as a cofactor for key enzyme complexes inside mitochondria, the energy-producing structures in every cell. What makes it unusual among nutrients is that it also works as a potent antioxidant, capable of recycling other antioxidants like vitamin C and glutathione. This dual role has made it one of the more studied dietary supplements for conditions involving oxidative stress, nerve damage, and skin aging.
How It Works in Your Cells
Your body synthesizes small amounts of alpha lipoic acid using building blocks from fatty acid production and iron-sulfur clusters. Once made, it attaches to several critical enzyme complexes inside mitochondria. These include the enzyme that converts pyruvate (a breakdown product of glucose) into usable fuel, the enzyme that drives a key step in the citric acid cycle, and the enzyme that processes branched-chain amino acids from protein. Without lipoic acid, these complexes can’t function, which means cells can’t efficiently turn carbohydrates, fats, or proteins into energy.
Beyond its role in energy metabolism, ALA stabilizes and regulates these multienzyme complexes. It’s required for normal cell growth, mitochondrial activity, and the coordination of how your body switches between burning different fuels throughout the day.
A Unique Type of Antioxidant
Most antioxidants work in either water-based or fat-based environments, but alpha lipoic acid operates in both. This means it can protect cell membranes (which are fatty) and the watery interior of cells. Its reduced form, dihydrolipoic acid (DHLA), gives it an additional trick: it can regenerate other antioxidants after they’ve been “used up” neutralizing free radicals.
Specifically, cells pre-treated with ALA show an increased capacity to recycle the oxidized form of vitamin C back into its active, protective state. ALA also restores intracellular levels of glutathione, the body’s primary built-in antioxidant, which naturally declines with age. This recycling ability is why ALA is sometimes called a “universal antioxidant,” though that label oversimplifies a more nuanced picture.
Food Sources and Supplement Forms
Alpha lipoic acid is present in many foods, but only in tiny amounts. The richest animal sources are organ meats: kidney, heart, and liver contain roughly 1 to 3 micrograms per gram of dry weight. Among vegetables, spinach and broccoli top the list, with tomatoes, peas, and Brussels sprouts containing about half that concentration. To put that in perspective, you’d need to eat enormous quantities of these foods to reach the doses used in supplement studies, which typically range from 300 to 600 mg per day.
Supplements come in two main forms. Most products contain a 50/50 mix of R-lipoic acid (the form your body naturally produces) and S-lipoic acid (a mirror-image version created during manufacturing). Some products sell pure R-lipoic acid, marketed as more bioavailable since it’s the naturally occurring form. Both versions are absorbed from the gut, though taking ALA on an empty stomach generally improves absorption since food can reduce how much reaches your bloodstream.
Nerve Health and Diabetic Neuropathy
The most clinically studied use of ALA supplements is for diabetic peripheral neuropathy, the tingling, numbness, and burning pain that develops when chronically high blood sugar damages nerves. ALA has been used for this purpose in Germany for decades, and doses in clinical trials have ranged from 600 mg to 1,800 mg per day.
The evidence, however, is more modest than early enthusiasm suggested. A Cochrane systematic review, considered the gold standard for evaluating medical evidence, found that ALA compared with placebo probably has little or no meaningful effect on neuropathy symptoms after six months of oral use. The average improvement in symptom scores fell well below the threshold considered clinically meaningful. Some shorter-term studies using intravenous ALA have shown more promising results, but the everyday oral supplement form hasn’t delivered the same level of benefit in rigorous trials.
Skin Aging and Topical Use
Applied directly to skin rather than taken orally, ALA has shown more consistent results. A study published in the Aesthetic Surgery Journal tested a 5% alpha lipoic acid cream applied twice daily for 12 weeks. Participants saw near-complete resolution of fine lines around the eyes and upper lip, a 50% reduction in the depth of medium vertical lip lines, noticeably smaller pore size, and overall improvement in skin color and texture. No adverse side effects were reported.
These benefits likely stem from ALA’s antioxidant activity at the skin’s surface, where it can neutralize free radical damage from UV exposure and pollution. The cream used a lecithin base with a penetration enhancer to help ALA absorb into the skin, so not all topical products may deliver the same results depending on their formulation.
Weight Loss and Inflammation
ALA supplements are sometimes marketed for weight loss, but the clinical data doesn’t support this claim strongly. A meta-analysis of randomized controlled trials using 600 mg per day found no significant changes in body weight or BMI. Where ALA did show a measurable effect was in reducing markers of inflammation: blood levels of C-reactive protein (a marker of systemic inflammation), total cholesterol, and LDL cholesterol all dropped modestly. These anti-inflammatory effects may have value on their own, but they didn’t translate into meaningful weight changes in the studies reviewed.
Side Effects and Practical Considerations
At typical supplement doses of 300 to 600 mg per day, ALA is generally well tolerated. The most commonly reported side effects are nausea, stomach discomfort, and skin rash. Higher doses, particularly above 1,200 mg per day, increase the likelihood of gastrointestinal issues.
Because ALA can improve insulin sensitivity and lower blood sugar, people taking diabetes medications should be aware it could amplify their effects, potentially causing blood sugar to drop too low. ALA may also affect thyroid hormone levels, which is relevant for anyone on thyroid medication. Taking it on an empty stomach, about 30 minutes before a meal, improves absorption but can also increase the chance of stomach upset, so some people split their dose across the day to balance both concerns.