Inhaling Insulin May Improve Memory of Alzheimer's Patients

Could daily sniffs of insulin boost your memory? Even more crucial, could they improve the memories of Alzheimer's patients? Preliminary, yet building, evidence suggests so.

A small study in the November Psychoneuroendocrinology found that healthy young persons' memories can profit from inhaling insulin. The lead investigator was Christian Benedict, M.D., a nutrition scientist at the University of Lübeck in Germany.

In this trial, 38 healthy individuals aged 18 to 34 years sniffed either 40 I.U. of insulin four times a day during an eight-week period or saline (a placebo) four times a day during the same period. Both at the start of the study and seven weeks into it, the researchers had the subjects learn words, then try to recall them a week later. Neither group's delayed word recall was as good at the end of the study as it had been at the start—apparently because of false recall of words from previous word lists. Nonetheless, the group getting insulin performed significantly better at delayed word recall at the end of the study than did the placebo group.

“Results indicate a direct action of prolonged intranasal administration of insulin on brain functions, improving memory... in the absence of systemic side effects,” Benedict and his colleagues concluded. “These findings could be of relevance for the treatment of patients with memory disorders like Alzheimer's disease.”

Intravenous insulin was known to improve memory before Benedict and his team found that intranasal insulin can also do so, and it was that discovery that spurred Benedict and his coworkers to undertake their study. The advantage of using intranasal rather than intravenous insulin, however, is that it does not cause systemic side effects like hypoglycemia.

At the 2003 annual meeting of the Society for Neuroscience, Suzanne Craft, Ph.D., a professor of psychiatry at the University of Washington, and colleagues reported the results from a small trial indicating that insulin sniffs can boost memory in both healthy older adults and persons with Alzheimer's, but especially the latter. The study included 20 healthy older adults and 10 Alzheimer's patients. On three separate visits, the subjects received intranasal administration of saline or one of two insulin doses (20 I.U. or 40 I.U.).

Shortly after administration, subjects were tested on story recall. Both the healthy subjects and the Alzheimer's subjects performed significantly better after getting insulin than getting a placebo, and the effect was even greater in the latter.

Another pilot trial by Craft and coworkers, in fact, suggests that giving a medication that boosts insulin's activity may be a way of halting memory loss in Alzheimer's patients. The medication is rosiglitazone, which is used to treat insulin resistance linked with type 2 diabetes. Results of this trial were reported at the Ninth International Conference on Alzheimer's Disease and Related Disorders in July.

GlaxoSmithKline, rosiglitazone's manufacturer, is conducting a larger trial to explore further the medication's seemingly salutary effect on memory in Alzheimer's.

How insulin might improve memory remains to be determined. Intranasally administered insulin is known to enter the cerebrospinal fluid, and insulin receptors have been detected in the hippocampus, a prime memory center in the brain.

And while the means by which rosiglitazone might stop memory loss in Alzheimer's patients is unknown, scientists suspect that it may not only alter brain levels of insulin, but also change brain levels of beta-amyloid protein—purportedly a major culprit in the Alzheimer's disease process.

An abstract of the study, “Intranasal Insulin Improves Memory in Humans,” can be accessed online at<www.sciencedirect.com> by clicking on “Browse Journals,” “P,” and then“ Psychoneuroendocrinology.” The two studies reported by Craft and coworkers at scientific meetings are under review by scientific journals. Information about the GlaxoSmithKline rosiglitazone memory trial can be obtained by e-mail at [email protected].▪