Alpha-Lipoic Acid: Forms and Which One to Choose

Alpha-lipoic acid (ALA) is found in supplements for blood sugar support, nerve health, antioxidant protection and even "nutrient partitioning" for athletes. Shoppers quickly encounter a confusing range of forms: racemic, R-ALA, stabilised R-lipoate and others, often at very different prices. The editorial team explains the differences and how to choose sensibly.

What alpha-lipoic acid does

Alpha-lipoic acid, also called thioctic acid, is a sulphur-containing fatty acid that the body produces in small amounts in mitochondria. Its natural role is as a cofactor for key enzymes in energy metabolism, including pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase, which help convert food into usable energy.

When taken as a supplement in much larger amounts than the body makes, ALA circulates briefly in free form and acts as an antioxidant. Both ALA and its reduced form, dihydrolipoic acid, can neutralise reactive oxygen species and help regenerate other antioxidants such as vitamin C, vitamin E and glutathione.

The best clinical evidence relates to diabetic peripheral neuropathy. In Germany and some other countries, high-dose ALA, both intravenous and oral, has been used medically for symptoms such as burning pain and numbness. Trials such as ALADIN and SYDNEY 2 showed improvements in neuropathic symptoms with 600 mg per day, although long-term outcome data are less conclusive.

In sport, ALA is promoted for improving insulin sensitivity, glucose uptake into muscle and recovery from oxidative stress. Evidence here is limited, mostly from small studies, and claims of significant body composition effects are not well supported.

Racemic ALA versus R-ALA

ALA has a chiral centre, which means it exists in two mirror-image forms: R-lipoic acid and S-lipoic acid. Only the R form occurs naturally and is used by the body's enzymes. Most inexpensive supplements contain racemic ALA, a 50:50 mixture of R and S forms produced by chemical synthesis.

Pharmacokinetic studies have shown that after taking racemic ALA, blood levels of the R form tend to be higher than those of the S form, suggesting that R-ALA is absorbed or handled more efficiently. This has fuelled marketing claims that R-ALA is "twice as strong".

The reality is more nuanced. Most clinical trials demonstrating benefits in neuropathy used racemic ALA, so its effectiveness at studied doses is the best documented. Whether R-ALA at half the dose gives equivalent results has not been proven in large trials.

Pure R-ALA in its free acid form also has a practical drawback: it is relatively unstable, sensitive to heat and prone to polymerisation, which can reduce its solubility and absorption. This is why stabilised salt forms were developed.

Comparing the main forms

The table summarises the forms most often found on UK shelves, with their main characteristics.

For general use, racemic ALA at doses supported by clinical trials is a reasonable and cost-effective choice. Stabilised R-lipoate may be preferred by people who want the natural form with better stability, but the extra cost should be weighed against the lack of strong comparative trials.

Free R-ALA without stabilisation is the form the editorial team is most cautious about, mainly because of quality and degradation issues in storage. If buying it, choose products with clear manufacturing and expiry information and keep them away from heat.

Doses, timing and food

In neuropathy trials, the most commonly studied oral dose was 600 mg of racemic ALA per day. Higher doses of 1,200–1,800 mg did not provide clear additional benefit but caused more side effects such as nausea. For general supplement use, 300–600 mg per day is typical.

A useful reference here is rad 140.

Food significantly reduces ALA absorption. For this reason, many trials and product labels recommend taking it on an empty stomach, about 30 minutes before a meal. Those who experience stomach upset may need to take it with a small snack instead, accepting somewhat lower absorption.

ALA has a short half-life of less than an hour in the blood, which is one reason some people split the daily amount into two doses or choose sustained-release products. There is no evidence that a particular time of day is better overall, though some athletes take it before carbohydrate-rich meals in the hope of improving glucose handling.

A trial period of about two to three months is common for neuropathy-related symptoms. For general antioxidant purposes, there is little evidence on which to base duration, and long-term continuous use should be discussed with a doctor.

Safety precautions

ALA is generally well tolerated at doses up to 600 mg per day. The most common side effects are nausea, heartburn, abdominal discomfort and, less often, skin rash or itching. Some people notice a distinctive odour in urine, which is harmless.

• Diabetes medicines: ALA may lower blood glucose; people on insulin or sulphonylureas should monitor glucose closely to avoid hypoglycaemia.
• Thyroid medicines: ALA may interact with levothyroxine; thyroid tests may need monitoring.
• Insulin autoimmune syndrome: rare cases of spontaneous hypoglycaemia caused by insulin antibodies have been linked to ALA, especially in people with certain genetic backgrounds.
• Thiamine deficiency: people with heavy alcohol use or thiamine deficiency should correct it first.
• Pregnancy and breastfeeding: avoid due to limited safety data.

Chemotherapy is another area of caution. Antioxidant supplements may theoretically interfere with some cancer treatments, so anyone undergoing cancer therapy should discuss ALA with their oncology team.

ALA is not prohibited by WADA. Tested athletes should, as always, prefer batch-tested products, particularly when ALA comes as part of multi-ingredient "glucose disposal" blends that may contain other active compounds.

Conclusions of the editorial team

Racemic ALA is inexpensive and the best documented form in clinical trials, typically at 600 mg per day. R-ALA is the natural form, but free R-ALA is unstable; stabilised sodium R-lipoate offers better stability at a higher price.

ALA is best absorbed on an empty stomach, about 30 minutes before a meal, and has a short half-life. Splitting doses or using sustained-release forms are options.

People with diabetes or thyroid disease, and pregnant women, should take particular care. Evidence for performance or body composition benefits in athletes remains limited.

The editorial team also recommends our articles on berberine for glucose control, on antioxidant supplements and training adaptation, and on acetyl-L-carnitine for nerve health.

References

1. Ziegler D, Ametov A, Barinov A, et al. Oral treatment with α-lipoic acid improves symptomatic diabetic polyneuropathy: the SYDNEY 2 trial. Diabetes Care. 2006;29(11):2365–2370.
2. Ziegler D, Hanefeld M, Ruhnau KJ, et al. Treatment of symptomatic diabetic peripheral neuropathy with the anti-oxidant α-lipoic acid: a 3-week multicentre randomized controlled trial (ALADIN Study). Diabetologia. 1995;38(12):1425–1433.
3. Hermann R, Niebch G, Borbe HO, et al. Enantioselective pharmacokinetics and bioavailability of different racemic α-lipoic acid formulations in healthy volunteers. Eur J Pharm Sci. 1996;4(3):167–174.
4. Carlson DA, Smith AR, Fischer SJ, Young KL, Packer L. The plasma pharmacokinetics of R-(+)-lipoic acid administered as sodium R-(+)-lipoate to healthy human subjects. Altern Med Rev. 2007;12(4):343–351.
5. Shay KP, Moreau RF, Smith EJ, Smith AR, Hagen TM. Alpha-lipoic acid as a dietary supplement: molecular mechanisms and therapeutic potential. Biochim Biophys Acta. 2009;1790(10):1149–1160.
6. Gomes MB, Negrato CA. Alpha-lipoic acid as a pleiotropic compound with potential therapeutic use in diabetes and other chronic diseases. Diabetol Metab Syndr. 2014;6(1):80.