How Cod Saved the Vikings

When I was in the Lofoten Islands in northern Norway, I came across one of the strangest sights I have ever seen: cod. [♫ ominous low tone fades in ♪] Hundreds of thousands of them, strung up on racks, [♫ ominous low tone fades in ♪] their stench blanketing entire villages. This annual massacre has been going on for over a thousand years, and it may be the very reason the Vikings existed.

♫ The poles of our planet are hostile to life, especially human life. In the time before modern comforts, not only are the winters long and cold, they are also dark. And that is important. As humans migrated north across Europe, a strange illness emerged. It especially affected children: their bones grew soft and deformed; some died, others were painfully disfigured for life.

The condition became known as "rickets" in children and "osteomalacia" in adults. From studies of bones, we know it was prevalent as early as the Roman Empire, but likely much earlier. And doctors were powerless to cure the disease because no one knew what caused it. Scientific evidence only came to light in the early 1920s during an experiment in Vienna. It was discovered that children with rickets recovered miraculously after they were regularly allowed to play outside on a balcony.

Scientists realized, without fully understanding why, that sunlight is essential for the development of healthy human bones. Today, we understand what's happening: ultraviolet light from the Sun strikes cholesterol molecules just under the surface of our skin. And it activates them to become vitamin D. This vitamin D is essential for absorbing the calcium necessary to form strong, healthy bones.

But north of 42 degrees latitude, there isn't enough sun in the winter months to form 𝘢𝘯𝘺 vitamin D; hence the epidemic of rickets. The notable exception here is the Vikings. They occupied what is now Denmark, Norway, and Sweden, well north of the 42nd parallel, and yet they had a reputation for being an imposing fighting force. Over 1,200 years ago, they raided towns all along the coasts of Europe. They laid siege to Paris!

The Vikings were intrepid sailors, voyaging out across the seas, establishing colonies in Iceland and Greenland. They even reached North America, the first Europeans to do so, 500 years before Christopher Columbus. So why weren't they overcome by the debilitating illness of rickets? Well, because although Scandinavia is cursed with a lack of sunlight, the cure is swimming just offshore. That's right — cod.

♫ Ungh! That is one big fish! This fish was an essential food source, but even more than that, it was a source of vitamin D. In the oily flesh and particularly in the fish's liver. That is a big cod liver. Just one meal of cod with liver and eggs supplies enough vitamin D to last you a month. And your body can store it because vitamin D is fat-soluble.

To survive the dark winter months and to build strong, healthy bones in children, cod was essential. So were the Vikings just lucky? I mean, they lived in a part of the world that is virtually uninhabitable due to its lack of sunlight, if not for the cod. Without cod, there likely never would have been a large, thriving population of warriors in northern Europe. So is cod the only reason we still know about the Vikings? Did cod, in a sense, create the Vikings?

Well, I think it's more complicated than that. The Vikings figured out how to use the cod to promote better health. One practice they passed down from generation to generation was extracting oil from the cod's livers—the part of the cod that is richest in vitamin D. So, was this science? I mean, I think it's tempting to think the Vikings figured out something that remained a mystery to modern medicine for over a millennium, but I think it probably went something like this: maybe some people noticed that cod liver oil drinkers were healthier, or their children taller, sturdier than those living further inland.

And so, the cultural practice of drinking cod liver oil spread, like evolution, but for ideas. Humans living together, observing one another, and emulating what works is a kind of proto-science. It's like running numerous uncontrolled experiments, but carried out over a whole population for generations. Some of what comes out of that is likely to have a basis in truth.

And the culture served as the memory of the population of people. This is essential because life is complicated; there are so many different things in nature and so many interactions that to have to encounter each one anew would be chaotic and overwhelming. We are able to function in the world because of the knowledge handed down to us, both explicitly, but also implicitly, by way of our culture.

Tradition can be a way of encoding knowledge—a way for us to build on those who came before, especially in a time before systematic teaching or books. The Vikings clearly understood that cod and cod liver oil were beneficial, but not exactly how beneficial or why. In the Greenland Viking settlement, that cultural knowledge was apparently forgotten. There, the Viking settlers turned to farming as their main source of subsistence, and without as much cod in their diets, the lack of vitamin D was crippling—literally.

Exhumed bones revealed that among genetic deformities, there are the tell-tale signs of rickets: spine curvature, deformation of arms and legs, and narrowed pelvis, and overall bone deformation and fractures. The Greenland colony vanished about 500 years ago, and vitamin D deficiency was one of the likely causes. If the Vikings had a scientific understanding of how important cod and cod liver oil were to their survival, they never would have stopped taking it.

In the absence of science, traditional knowledge is often the best place to start. In fact, cod liver oil was actually the substance in which the first vitamin was scientifically identified: vitamin A. And later the fourth, vitamin D. But cultural knowledge is also 𝘯𝘰𝘵 science. There are harmful practices like bloodletting mixed in with the helpful ones.

And without knowledge of clear cause-and-effect, the importance of some practices, like taking the cod liver oil, can be forgotten. It was the British who realized, through the first known randomized control trial, that citrus fruits cure scurvy. And as a result, it was their fleet, rather than say the Vikings, that came to dominate the seas.

♫ I would argue that the scientific method is the greatest technology humans have ever developed. It allows us to understand not only what works but why it works. And with that knowledge, our future is determined not by luck, but by our ability to manipulate reality to our advantage.

This video was made with excerpts from my feature-length documentary, Vitamania. So if you want to watch it for a couple of bucks, click this link to find out how. I want to say a huge thank-you to our funding partners and to Gene Pool Productions, with whom I made this film. Vitamania, it's all about the sense and nonsense of vitamins.