Contrary to popular belief, the tryptophan in turkey is not to blame for your sleepiness, and sudden need for a nap, after you eat a bountiful Thanksgiving dinner. It’s time for you and Uncle Charlie and Aunt Sally to stop attributing your desire to go supine on the couch, post-holiday feast, to this dietary amino acid, which is present in all poultry and many other foods. The perpetuation of the tryptophan-in turkey-makes-you-sleepy myth must end!
If tryptophan in food were the sedative that people think it is, you would be falling asleep any time you consumed chicken, a dinner staple that contains more tryptophan than turkey does, and no one would be awake in the evening. Other foods high in tryptophan include some cheeses, nuts, and seeds; milk; eggs; tofu; red meats; fish; oats; beans and lentils.
Tryptophan does have hypnotic properties, but very little of what you ingest in foods travels from your bloodstream to your brain because of the blood-brain barrier, which is comprised of special cells that collectively act as a brain gatekeeper, determining which substances get in. The ability of a substance (e.g., a drug) to cross this barrier was perhaps most famously relevant in studies in the 1960s of dopamine and L-DOPA as possible treatment for Parkinson’s disease. Dopamine does not cross the blood-brain barrier, but its amino-acid precursor, L-DOPA, does. Once in the brain, L-DOPA converts to dopamine.
The actual soporifics of Thanksgiving Day are overeating, which rachets up your digestive process, requiring your body to expend more energy than usual; drinking alcohol, which is a depressant; and taking time off from work and other responsibilities to enjoy family and friends, which puts you in a mental state of relaxation. Sorry. Your turkey’s tryptophan is not a culprit, just an innocent bystander.
Amino acids, such as tryptophan, are important components of protein synthesis in the human body, and proteins make our bodies functional at the cellular level. Tryptophan is one of the 20 so-called essential amino acids. It is also one of the nine essential amino acids that our bodies don’t manufacture, so all of the tryptophan that we consume and store must come from the foods we eat.
Tryptophan is the sole amino-acid precursor to the body’s synthesis of the important hormone-neurotransmitter, serotonin, which, in turn, is a precursor in the synthesis of the hormone melatonin, which regulates the sleep-wakefulness cycles (circadian rhythms) that I discussed in my last blog, “The Sleep-Wakefulness Cycle and REM Sleep: Remembering a Historic Duo, as Daylight Saving Time Ends” (11/3/17).
In pioneering research at the National Heart Institute of the National Institutes of Health in the 1950s, my father and his young team identified serotonin in bananas and other foods and determined, fortunately, that it has no physiologic effect on the person who eats these foods because it does not cross the blood-brain barrier. (Among their many findings in food research, they also measured dopamine and norepinephrine in bananas.)
In a post-Thanksgiving blog, I will recount the story of Dad’s discovery with Dr. John A. Oates III, who became a preeminent clinical pharmacologist and enjoyed an illustrious career at Vanderbilt medical school, of what they called tryptophan “intoxication.” They were the first to demonstrate a pharmacologic effect of tryptophan—which they gave in oral supplements—in human beings. But they never received credit for it.
I was remiss in not telling you what became of the “historic duo” that I featured in my last blog, as well as the third participant in the breakthrough REM sleep studies, Dr. William C. Dement. People live on after they break through, and I always find it interesting to see how they fared. (In part, I wonder if what goes around truly comes around.)
The following is material that I largely excerpted from my book, “Starting With Serotonin: How a High-Rolling Father of Drug Discovery Repeatedly Beat the Odds”:
Dr. Nathaniel Kleitman (Ph.D., physiology), considered the U.S. father of modern sleep research, retired in 1960 from the University of Chicago, but continued working well into his 80s. In 1982, he proposed the existence of a basic rest-activity cycle (BRAC) in adults that operates around the clock and lasts about 90 minutes. In wakefulness, he said, the activity phase of the BRAC coincides with a call for nourishment, which people, busy with work, school, or recreation, usually ignore. Kleitman died in his sleep in 1999 at age 104.
Beset by personal problems, including his wife’s suicide and his own persistent depression, Dr. Eugene Aserinsky (Ph.D., physiology), Kleitman’s disdainful and mercurial student-associate, produced no science for 10 years after the REM sleep discovery. Eventually, he engaged in undistinguished sleep studies involving rapid-eye movement and respiration and published about 20 papers. Aserinsky taught at the Jefferson Medical College in Philadelphia for 22 years, but resigned after being passed over for the physiology chairmanship. In 1976, he became chairman of physiology and pharmacology at Marshall University in West Virginia. He retired in 1987.
In July 1998, the 77-year-old Aserinsky fell asleep at the wheel and was killed instantly in a one-car accident in Carlsbad, Calif.
As I mentioned in my previous blog, Bill Dement opened the nation’s first clinical sleep center at Stanford University. Seven years later, the psychiatry professor, who had an M.D. and a Ph.D. in physiology, established the Stanford University Sleep Disorders Clinic.
Dement specialized in narcolepsy and sleep apnea. Among his many achievements, he co-developed the Multiple Sleep Latency Test, which measures levels of daytime alertness. Although the test grew out of the professor’s desire to monitor his narcoleptic patients, he used it effectively in a 10-year longitudinal study of adolescents’ sleep and daytime alertness, exposing a new understanding about circadian rhythms in this age group. (For example, they aren’t very alert during early morning hours, when school may already be in session.) Dement retired from teaching in 2003.
Considered the U.S. father of sleep medicine—the king of sleep research and disorders, as Dad called him—Dement published a brief statement about the REM sleep discovery in 1974, suggesting it was a team effort. See William C. Dement, Some Must Watch While Some Must Sleep (San Francisco: W.H. Freeman & Co., 1974), pp. 24-25.
Now 89 years old, Dement is an emeritus professor in the department of psychiatry and behavioral sciences at the Stanford Center for Sleep Sciences and Medicine.
Happy Thanksgiving, everyone. Enjoy your naps.