Our story takes place in the northernmost county of Sweden, in a picturesque collection of villages beside the river Kalix. These days about 3,700 people live in Överkalix, descended from 15th century settlers.
It is a tough place to live. When I say north, I mean north – north of the Arctic Circle. For six months of the year, the sun barely rises. Historically, people survived by fishing for salmon, keeping livestock and depended on the annual harvest of barley and rye to get though the winter.
Looking back, you can see a clear boom and bust cycle of crop success. In 1799, 1801, 1813–15, 1822, 1825–26, 1841, 1853 and 1879, the long growing days of the far-northern summer resulted in huge surpluses of food and the people of Överkalix gorged themselves.
But equally unpredictably, years of total or near total crop failures followed especially harsh winters. People didn’t starve to death; they hunted small birds and made bread from the inner bark of fir trees. But it was certainly slim pickings – only a tiny fraction of the normal amount of food was available.
How do we know?
Clergymen and other officials in Överkalix have kept meticulous records of every harvest for three centuries now. By adding other information like food prices, scientists have been able to reconstruct the nutrition available to generations of Överkalix families.
Why do we care about the nutrition of 19th century Swedes?
Because the same clergymen kept detailed records of every birth, death, cause of death and family lineage during the same period. What this amounts to is an incredible natural experiment allowing us to ask the questions “What are the life-long health effects of starvation and over-eating?”
And this is where our story gets interesting.
Imagine you are a boy growing up in Överkalix and between the ages of nine and twelve you experience at least one season of famine. You go on to have sons and grandsons. It turns out that your grandsons receive a significant health boost from your suffering. They have only one-quarter the risk of developing heart disease, a lower chance of developing type 1 diabetes and on average, live 30 years longer than if their grandfather experienced a season of feasting at the same age. That’s not a typo — I really mean 30 years!
The reverse is also true. If your grandfather experienced at least one season of feast, the effects on your health are negative. For example, you have a 400% increased risk of dying as a result of type 1 diabetes. All because your grandfather experienced one season of starvation or gluttony just before puberty.
Think I’m making it up? Could these crazy results be true?
What’s going on just before puberty?
It turns out they are. The ages of nine to twelve are known as the “slow growth period” in boys. On the outside not much is happening other than the fact that boys suddenly stop growing taller. But on the inside lots is going on and we know that environmental factors can have a big effect on the body. In particular, boys at this age are putting aside the cells that will later become sperm cells. And the experience of famine or feast is chemically marking these cells and the marks are being carried down through generations.
It took a long time for these results to be accepted by the scientific world. The story had always been that you were born with your DNA (half from your Mum, half from your Dad) and your DNA was your blueprint.
The Överkalix story (and many others now) tells us that even if your DNA sequence essentially doesn’t change during your life, there can be changes in the activity of our genes and they can be passed down through generations.
This is the science of epigenetics – literally: above genes. Think of your DNA as the hardware and your epigenome the software.
Basically, there is a system of switches that can turn genes on or off controlled by environmental factors like nutrition.
So is it good or bad news for us? Probably both. It means lifestyle choices you make like smoking and over-eating aren’t just affecting you, they may also predispose your kids and grandkids to disease and early death before they are even born. No pressure…
But equally, our choices now could leave a pretty amazing legacy.