Caffeine is one of the most popular stimulants in the world and is most commonly consumed in coffee. People turn to caffeine to wake up in the morning and to stay energized throughout the day, but there’s a downside: Too much caffeine can keep you awake even when you’re ready to sleep.

The key to this unwanted aftereffect is a compound called adenosine, a byproduct of neuron activity in the brain. Receptors in our nervous systems constantly monitor adenosine levels, and, when they drop below a certain point in the brain and spinal column, the body readies itself for sleep. Caffeine seeks out specific adenosine receptors and mimics adenosine’s effects, in essence tricking the body into thinking sleep time is a long way off.

How long a dose of caffeine affects the body can vary according to a number of factors, including tolerance, genetics, and physical health. In most cases, however, the effects last about five or six hours. Longtime coffee drinkers may experience a tolerance to caffeine that requires them to consume increasing quantities to achieve the same stimulant effect. If they stop drinking coffee cold turkey, they may experience withdrawal symptoms such as headaches, irritability, and nausea.

To prevent caffeine-related sleep issues, it is recommended that caffeine consumption be limited to four cups of coffee per day and that the last cup be consumed no later than midafternoon. Switching to caffeine-free coffee or tea can also help. Children and adolescents should avoid heavy caffeine consumption, according to the American Academy of Pediatrics.

“Let them eat cake” is the most famous quote attributed to Marie-Antoinette, the queen of France during the French Revolution. As the story goes, it was the queen’s response upon being told that her starving peasant subjects had no bread. Because cake is more expensive than bread, the anecdote has been cited as an example of Marie-Antoinette’s obliviousness to the conditions and daily lives of ordinary people. But did she ever actually utter those words? Probably not.

For one thing, the original French phrase that Marie-Antoinette is supposed to have said—“Qu’ils mangent de la brioche”—doesn’t exactly translate as “Let them eat cake.” It translates as, well, “Let them eat brioche.” Of course, since brioche is a rich bread made with eggs and butter, almost as luxurious as cake, it doesn’t really change the point of the story. But the queen wouldn’t have been referring to the sort of dessert that English speakers often imagine.

More important, though, there is absolutely no historical evidence that Marie-Antoinette ever said “Qu’ils mangent de la brioche” or anything like it. So where did the quote come from, and how did it become associated with Marie-Antoinette?

As it happens, folklore scholars have found similar tales in other parts of the world, although the details differ from one version to another. In a tale collected in 16th-century Germany, for instance, a noblewoman wonders why the hungry poor don’t simply eat Krosem (a sweet bread). Essentially, stories of rulers or aristocrats oblivious to their privileges are popular and widespread legends.

The first person to put the specific phrase “Qu’ils mangent de la brioche” into print may have been the French philosopher Jean-Jacques Rousseau. In Book VI of Rousseau’s Confessions (written about 1767), he relates a version of the story, attributing the quote to “a great princess.” Although Marie-Antoinette was a princess at the time, she was still a child, so it is unlikely that she was the princess Rousseau had in mind.

Since Rousseau’s writings inspired the revolutionaries, it has sometimes been supposed that they picked up on this quote, falsely credited it to Marie-Antoinette, and spread it as propaganda, as a way to rouse opposition to the monarchy. However, contemporary researchers are skeptical of such claims, having found no evidence of the quote in newspapers, pamphlets, and other materials published by the revolutionaries.

Amazingly, the earliest known source connecting the quote with the queen was published more than 50 years after the French Revolution. In an 1843 issue of the journal Les Guêpes, the French writer Jean-Baptiste Alphonse Karr reported having found the quote in a “book dated 1760,” which he said proved that the rumor about Marie-Antoinette was false. Rumor? Like so many of us, he was probably just repeating something he had heard.