Preventing Alzheimer's with Herbs

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In medieval Europe, rosemary was much beloved, signifying friendship and remembrance. Modern science shows that this reputation has some substance—this flavorful culinary herb contains phytochemicals that have potential for treating and preventing Alzheimer’s disease and related dementias.

The mechanics of memory

Research shows that rosemary affects a neurotransmitter in the brain called acetylcholine that transmits nerve impulse signals from one neuron to another. Acetylcholine is crucial in the areas of the brain where memories are ­created and stored. If nerves and neurons are a sort of living wiring ­system, acetylcholine and other ­neurotransmitters are “switches” that turn on to make a connection between two nerve “wires,” then turn off after the connection is made and the information has been correctly transmitted.

After acetylcholine transmits a nerve signal, it’s broken down rapidly by an enzyme called acetylcholinesterase. This cycle of breaking down and rebuilding acetylcholine prevents the neuron from “shorting out” after receiving a signal. If the acetylcholine switch stays on, the brain can’t tell where one signal ends and the next begins.

In the case of Alzheimer’s, it’s thought that acetylcholine levels are either too low or that acetylcholine is broken down too fast, so some nerve impulses carrying memory or learning information can’t be fully transmitted. In either case, slowing or inhibiting the action of acetylcholinesterase may help improve memory, and researchers are on the lookout for compounds that do this ­safely. Drugs with this action are among the few that have proven successful in Alzheimer’s treatment. Rosemary was one of the first plants identified as having the same inhibiting power.

Rosemary’s cousins

Rosemary is not the only herb with this talent. In fact, most of rosemary’s cousins also inhibit acetylcholinesterase. Rosemary (Rosmarinus officinalis) belongs to the mint family and is related to peppermint, spear­mint, and pennyroyal, although these mints are from the genus Mentha. A 1998 Japanese study tested essential oils from thirty-one Mentha species and varieties and found that most inhibited acetylcholinesterase, with the most effective being water mint (M. aquatica). Although various phytochemicals in the mints’ oils were tested individually, the whole essential oils were more effective, indicating that components in the oils act synergistically.

Maybe this follows the common sense of our senses: Doesn’t smelling or tasting these herbs pick you up? The appeal of mints and rosemary may be deeper than emotional or food-oriented attachments—it may extend all the way down to the level of brain chemistry.

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