The crew was suffering from scurvy, a disease that was then both bitterly familiar and deeply mysterious. No one knew why it struck sailors or how to cure it. But on that 1602 voyage, Ascensión witnessed what he considered a miracle. While the crew was ashore burying the dead, one sick sailor picked up a cactus fruit to eat. He started to feel better, and his crewmates followed his example.
“They all began to eat them and bring them back on board so that, after another two weeks, they were all healed,” the priest wrote.
Over the next two centuries, it gradually became clear that scurvy was caused by a lack of fruits and vegetables on long-distance voyages. In the late 1700s, the British Navy started supplying its ships with millions of gallons of lemon juice, eradicating scurvy. But it wasn’t until 1928 that the Hungarian biochemist Albert Szent-Gyorgyi discovered the ingredient that cured scurvy: vitamin C.
Szent-Gyorgyi’s experiments were part of a wave of early-20th-century research that pulled back the curtain on vitamins. Scientists discovered that the human body required minuscule amounts of 13 organic molecules. A deficiency of any of the vitamins led to different diseases — a lack of vitamin A to blindness, vitamin B12 to severe anemia, vitamin D to rickets.
Today, a huge amount of research goes into understanding vitamins, but most of it is focused on how much of them people need to stay healthy. This work does not address a basic question, though: How did we end up so dependent on these peculiar little molecules?
Recent research is providing new answers. It appears that vitamins were essential to life from its earliest stages some four billion years ago. Early life-forms could make their own vitamins, but some species — including ours — later lost that ability. Species began to depend on each other for vitamins, creating a complex flow of molecules that scientists have named “vitamin traffic.”
Every vitamin is made by living cells — either our own, or in other species. Vitamin D is produced in our skin, for example, when sunlight strikes a precursor of cholesterol. A lemon tree makes vitamin C out of glucose. Making a vitamin is often an enormously baroque process. In some species, it takes 22 different proteins to craft a vitamin B12 molecule.
While a protein may be made up of thousands of atoms, a vitamin may be made up of just a few dozen. And yet, despite their small size, vitamins expand our chemical versatility. A vitamin cooperates with proteins to help them carry out reactions they couldn’t manage on their own. Vitamin B1, for example, helps proteins pull carbon dioxide from molecules.
Vitamins carry out these chemical reactions not just in our own bodies but in all living things. “If you talk about bacteria, fungi, plants, humans — everybody needs them,” said Harold B. White III, a biochemist at the University of Delaware.
This universal chemistry is likely the result of evolution. Scientists generally agree that life on earth today evolved from a chemically simpler form perhaps four billion years ago. Those primordial organisms relied on a single-stranded variant of DNA, called RNA. Back then, RNA did double duty, carrying genes, the way DNA does today, and catalyzing chemical reactions, as proteins do now.
Dr. White was one of the first scientists to think seriously about this primordial “RNA world.” In 1975, he proposed that vitamins helped RNA molecules carry out their chemical reactions. While proteins took over those reactions, they still rely on the same vitamins. “There’s no way we’re going to get rid of them now,” he said.
When Dr. White offered up his theory, other scientists were skeptical. “People were saying, ‘How are you going to test it?’ ” he recalled. “I said, ‘I can’t.’ I didn’t see any way to do that work at the time.”
It took nearly four decades for technology to catch up. Dipankar Sen, a biochemist at Simon Fraser University in British Columbia, set out in 2007 to test Dr. White’s idea.
After six years of tinkering and testing, Dr. Sen and a graduate student, Paul Cernak, found an RNA molecule that could use vitamin B1 to pull carbon dioxide from another molecule. That is what proteins use B1 for today, just as Dr. White had predicted. Dr. Cernak and Dr. Sen described their experiment in Nature Chemistry.
Once the ability to make vitamins evolved, some species became especially good at making them. Plants, for example, evolved into vitamin C factories, packing their leaves and fruits with the molecule. At first, vitamin C probably defended plants against stress — a function it carries out in other species, including us. But over time, the vitamin took on new jobs in plants, like helping control the development of fruit.
It took hundreds of millions of years for plants to become such proficient vitamin C manufacturers, but vitamin production can change in far less time. Our own ancestors needed just thousands of years to alter their production of vitamin D. When humans left equatorial Africa and spread to higher latitudes, the sun was lower in the sky and supplied less ultraviolet light. By evolving lighter skin, Europeans and Asians were able to continue making a healthy supply of vitamin D.
Aside from vitamins D and K, we humans can’t make any of the vitamins we need to stay healthy. In some cases, our ancestors could make them, but lost that ability. Our mammalian ancestors 100 million years ago never got scurvy, for example, because they could make their own vitamin C.
Many vertebrates can make vitamin C, and use an identical set of genes to do so. “We should be able to make it, too, since we have all the genes,” said Rebecca Stevens of the French National Institute for Agricultural Research.
Unlike a frog or a kangaroo, however, we have crippling mutations in one of those genes, known as GULO. Unable to make the GULO protein, we cannot produce vitamin C.