Rambam on the Importance of Sound Sleep

How Long Should One Sleep?

Everyone knows that the body needs sound sleep in order to recover. Some studies indicate that 7 hours is the optimal amount of sleep, and that people who sleep more or less have shorter life expectancies. Only recently, researchers at Harvard University, led by Professor Robert Stickgold, concluded that a person requires exactly 8 hours of sound sleep for effective rest. They explain that nighttime sleep is divided into two stages, during which physiological and biochemical changes take place in the brain: the first part of the night and the second, pre-dawn stage—the final 2 hours of sleep. Together, these two stages of sleep strengthen memory and make it clearer. 1. During the first stage, information from the part of the brain responsible for memory—the hippocampus—moves to the cerebral cortex. Then, for approximately 4 hours, a slow process takes place in which the information absorbed during the previous day is divided up and transferred into the neural network of the brain’s nerve cells. This process somewhat resembles slowly rising “yeast dough,” explains Professor Stickgold. 2. During the second and final stage of sleep, known as “active sleep,” rapid biochemical changes once again take place in the brain. The hippocampus “disconnects” from the cerebral cortex, and the brain once again “replays” the information that has already been processed and archived in the nerve cells. At the same time, the connections between cells in all areas of memory are strengthened.   It is astonishing that the great Jewish physician—Rambam—Rabbi Moshe ben Maimon—Maimonides—already in the 12th century, long before all the various studies of sleep, left the Jewish people teachings about sound sleep. Rambam asserts that a person derives the maximum benefit from 8 hours of sleep and requires no more. In the Mishneh Torah, he writes: “Day and night together comprise 24 hours. A person needs only one-third of a day for sleep—that is, 8 hours. An allusion to this is found in Tanakh, in the Book of Job: כִּי עַתָּה שָׁכַבְתִּי וְאֶשְׁקוֹט יָשַׁנְתִּי אָז יָנוּחַ לִי “Ki-atah shakavti ve’eshkot yashanti az yanuach li”—(Now I would lie down and be quiet; I would sleep, and then I would rest.) (Job 3:13) Rambam explains that the gematria of the word “az”—אָז (then)—equals 8 (א = 1, and ז = 7). The verse seems to say: “If I had slept אָז (for just 8 hours), then I would have rested.” From this, Rambam concludes that the Almighty hints at the amount of time a person needs for sound sleep—exactly 8 hours. P.S. We know from Chazal that the Book of Job was written by Moshe Rabbeinu himself, the greatest of the prophets, who received all his information from the Almighty.   (Based on the book The Revolution by Zamir Cohen—translated by D. Levitan)