An evening milkshake spiked with the amino acid tryptophan may help clear the morning mental fog of the sleep-deprived, preliminary research suggests.

In a study of 28 healthy young adults, researchers found that accompanying an evening meal with a milkshake containing a protein powder called alpha-lactalbumin -- which delivers a high concentration of tryptophan -- seemed to improve morning alertness among participants who had mild sleep problems. "Good" sleepers, on the other hand, showed no such benefit.

The findings, published in the American Journal of Clinical Nutrition, suggest that the supplement sharpened certain participants' mental acuity by improving their sleep.

However, much more research is needed before tryptophan-laced milkshakes can be recommended as a sleep aid, according to lead study author Dr. C. Rob Markus of the University of Maastricht in the Netherlands.

Alpha-lactalbumin, or A-LAC, is a protein derived from the whey component of milk. It contains a high concentration of the essential amino acid tryptophan, a protein building-block best known for its sleep-inducing effects. In the body, tryptophan serves as a precursor for the brain chemical serotonin, which, among other things, is thought to help regulate sleep.

Tryptophan is found in foods such as beef, chicken, dairy products and, most famously, turkey -- which is often blamed for the near-coma that follows Thanksgiving dinner. In reality, however, the relatively low concentration of tryptophan in turkey and other foods is unlikely to affect the brain because it must compete with other amino acids and nutrients for absorption.

In their study, Markus and his colleagues examined whether an A-LAC protein powder, with its high concentration of tryptophan, could increase the ratio of tryptophan to other amino acids in participants' blood -- and whether there would be any difference in their mental alertness the next morning.

The protein powder, marketed as BioPure, was supplied by Eden Prairie, Minnesota-based Davisco Foods International.

Fourteen men and women with mild sleep problems, and 14 others without sleep complaints took part in two experiments on separate evenings -- one in which they consumed a tryptophan-fortified milkshake with dinner and later for a snack, and one in which they had "placebo" milkshakes that did not contain the A-LAC supplement.

The next morning, participants took a computerized test that measured their mental reaction times, while electrodes placed on their scalps recorded their brain activity.

Markus and his colleagues found that participants' blood levels of tryptophan were more than twice as high on the night they dined on the supplemented milkshakes compared with the placebo milkshakes.

More importantly, men and women who normally had sleep problems performed better on the mental-alertness test on the morning after having the tryptophan-containing milkshakes. On the other hand, tryptophan made no difference to the performance of the 14 participants with no sleep problems.

It's likely, according to Markus and his colleagues, that improved sleep explains the better test performance. They found that people who were normally "poor sleepers" reported less morning grogginess the day after having the tryptophan-fortified milkshakes.

However, it's too soon to start recommending the A-LAC supplement to the sleep-deprived, Markus told Reuters Health.

"A lot of research needs to be conducted before making any claims," he said.

Among the remaining questions is how the souped-up shakes might affect people with more-significant sleep problems. And in general, Markus noted, the precise role of tryptophan and serotonin in sleep is not fully understood. Though they appear to help regulate sleep-wake rhythms, he said, the magnitude of the influence is not clear.

SOURCE: American Journal of Clinical Nutrition, May 2005.