Studies in humans have found that 30-40 percent of alpha lipoic acid
taken by humans is absorbed by the body (1,2). This is a high rate
compared to many drugs. In fact, it can be said that alpha lipoic acid
is "readily and nearly completely absorbed" (2) by the body.
Commercially available alpha-lipoic acid is called racemic, consisting
of two forms, the R+ and S- optical isomers in equal amounts. It is a
synthetic product, attempting to mimic the body's natural forms of
alpha lipoic acid. Natural ALO consists only of the R isomers, making
RLA much more effective at being accepted into the body than the SLA
forms. RLA is reduced to R-DHLA, the body's potent antioxidant, 28
times faster than SLA. Studies have therefore not surprisingly found
that RLA is more bioavailable than SLA when taken orally. RLA was
found in one study to prevent cataracts in rats better than SLA.
Even though alpha lipoic acid supplements include 50% of the unnatural
and not-as-effective S form, the other half of the supplements
provides the benefits of the alpha lipoic acid supplement and has
great bioavailability, as mentioned above. There is no evidence that
the S form actually interferes with the R form. In addition, the RLA
form is better absorbed than the SLA form-- in a study, peak
concentrations of SLA were 40-50 percent less than peak concentrations
of RLA (and they are each 50% of the dosage).
Oral supplements of alpha lipoic acid are better absorbed on an empty
stomach than paired with food. Taking them with food decreases overall
plasma concentrations of the drug by 20% and peak concentrations by
1. Hermann R, Niebch G, Borbe HO, et al. Enantioselective
pharmacokinetics and bioavailability of different racemic alpha-lipoic
acid formulations in healthy volunteers. Eur J Pharm Sci.
2. Teichert J, Hermann R, Ruus P, Preiss R. Plasma kinetics,
metabolism, and urinary excretion of alpha-lipoic acid following oral
administration in healthy volunteers. J Clin Pharmacol.
"bioavailability alpha lipoic acid"
"s-la alpha lipoic acid"
If you need any other clarification or assistance, I'd be happy to help.