Arabinogalactins, substances found in many plants, are long molecules made of the sugars galactose and arabinose linked together in a chain. Arabinogalactan extracted from the Western larch tree (larch arabinogalactan, or LA) has been proposed as an immune stimulant.

Test-tube and animal studiessuggest that LA has several potentially positive effects on the immune system. It appears to activate a type of white blood cell called a “natural killer” or NK cell, and perhaps other white blood cells as well, and also possibly alter levels of immune-related substances such as interleukins, interferon, and properdin.1-5

On the basis of these findings, LA has been advocated as a supplement for general immune support. However, this recommendation is premature. It is a very, very long way from basic science of this type to evidence that a treatment has real effectiveness. Many plant substances appear to activate the immune system; this may be merely because the immune system regards them as “the enemy,” and mobilizes to fight them. It takesdouble-blind, placebo-controlled trials to determine whether theoretical effects translate into real life benefits, and thus far only one such study has been performed on LA as an immune stimulant. Unfortunately, this single meaningful trial was not designed to determine the actual medical benefits (if any) of LA. Rather, it primarily continued the theoretical investigation of LA’s effects on components of the immune system.

In this trial, 48 healthy women were assigned to receive one of four treatments: LA, echinacea, LA plus echinacea, or placebo.6 Researchers evaluated various laboratory measurements of immune function. The results failed to show that LA by itself had any effect on immunity.

Other extremely preliminary research hints that LA might enhance the effectiveness of drugs used in cancer treatment,7,10 help antibiotics fight ear infections and other infections, and enhance the immune system in people with conditions such as chronic viral hepatitis, HIV, and chronic fatigue syndrome.5 However, all these suggestions are highly speculative and lack reliable supporting evidence.

There no doubt, however, that LA is a good dietary fiber source. Like less expensive forms of fiber, it appears to have beneficial effects in the colon.11

A 6-month study failed to find LA helpful for improving cholesterol profile.12