A new theory holds that juvenile diabetes helped our ancestors not freeze to death
Sandra Blakeslee New York Times
When the temperatures outside drop, most people wrap themselves in thick sweaters, stay indoors, and eat. If an innovative theory published recently is correct, a few thousand years ago there was another way to keep warm: juvenile diabetes.
The patients with the disease, also known as type 1 diabetes, suffer from a high level of sugar (glucose) in the blood. According to the theory, juvenile diabetes developed in human ancestors who lived in northern Europe about 12 years ago, at a time when temperatures dropped by about 5.5 degrees Celsius in a few decades, and a new ice age began almost overnight.
Archaeological findings suggest that many simply froze to death, and that others fled south. Dr. Sharon Moalem, an evolutionary medicine expert at Mount Sinai Hospital School of Medicine in New York, believes that some have been able to adapt to the cold. According to him, a high level of blood sugar prevents the formation of ice crystals in cells and tissues. In other words, type 1 diabetes helped many of our ancestors not freeze to death. Moalem presented his theory about a month and a half ago, on the website of the magazine "Medical Hypotheses".
Dr. Clive Gamble of the University of London, a lecturer in geography and an expert on early human migration patterns, believes that the theory joins a growing body of evidence that Europeans were the descendants of hunters with endurance to cold climates, rather than farmers from warm regions. "As a Brit, it makes perfect sense to me," he says.
Moalem's thesis is met with great skepticism by most doctors who treat diabetes patients. "Well, really," said one of them. "Type 1 diabetes should end in ketoacidosis (a dangerous complication of diabetes) and death at a young age."
Not exactly, believes Moalem. In the past, the life expectancy of many was no more than 25 years. Those who suffered from high blood sugar did not live long enough to develop complications, but did manage to mature and reproduce, despite the extreme cold.
There are two types of diabetes. Type 1 appears when the immune system destroys cells that produce insulin, a hormone that helps transport glucose in the body. Type 2 occurs when cells in the body do not respond to normal amounts of insulin. Without insulin, sugar builds up in the blood. 90% of diabetes patients suffer from type 2 diabetes, mainly overweight adults. In contrast, says Moalem, type 1 diabetes, in which patients are mostly young people up to the age of 30, has characteristics that are difficult to explain. It is mainly common among the descendants of the inhabitants of Northern European countries. In Finland and Sweden the rate of patients with it is particularly high, but among African, Asian or Hispanic populations it is rare. The Indians in America and the native inhabitants of Alaska are almost never affected by the disease, unless they are of mixed race.
Moreover, type 1 diabetes is more common in winter than in summer. The blood sugar level of the patients increases in the cold months, regardless of their diet. In warmer climates, there is no seasonal change in sugar levels. When families with a genetic predisposition to the disease move to live in a warmer climate, the chance that one of them will develop diabetes decreases.
According to Moalem, many genes increase the chance of being affected by type 1 diabetes, and they are inherited from both parents. Beyond that, most experts believe that some environmental factor may cause the outbreak of the disease, such as a virus or cold air. Cold may activate a metabolic mechanism involved in the formation of type 1 diabetes, says Moalem. In fact, many of the metabolic changes seen in type 1 diabetics are the same as those seen in animals with cold tolerance.
Dr. Kenneth Storey, a biochemist from Carleton University in Ottawa, Canada, studies the meadow frog, which lives in high areas of the northern hemisphere, including the Pole. In winter, when the frog's fur begins to freeze, the liver releases sugars into the blood. This is how the freezing temperature of the body fluids decreases, and the proteins gain protective walls.
The frog produces such a large amount of sugars that eventually all its tissues are protected from the cold. She completely freezes. Her heart is not beating. The circulation is paralyzed, she is not breathing and her muscles are uncomfortable. In the spring the frog thaws and returns to its normal life. That is, the frog's diabetes is reversible.
Humans and animals exposed to the cold will shiver first, in order to warm up, says Moalem. However, afterwards they create heat by burning special fat - brown adipose tissue. The ability of this tissue to produce heat depends on large sugar reserves. No insulin is needed. Because of this, the diabetics can divert the sugars from the blood to the heating path of the brown adipose tissue.
Most of the cold adaptation mechanisms in bacteria, plants and animals have evolved gradually. However, findings from Greenland revealed a unique period in human history that could have forced humans in northern Europe to adapt more quickly to the cold, or die. About 14 years ago, temperatures in Europe began to drop rapidly. About 1,500 years later, the conditions changed. Every few decades the temperatures dropped. The freezing conditions lasted for about 1,300 years.
Although a similar ice age was recorded in North Asia at the same time, it does not seem to have happened with the same speed and intensity, says Moalem, in an attempt to explain why other populations living in cold climates did not develop similar protective responses to the cold. Instead - they developed defense mechanisms against hunger. In today's high-calorie world, they may actually be candidates for type 2 diabetes.
People who lived in the cold of Northern Europe could choose one of three ways - escape the cold, build good buildings and wear furs, or undergo biological adaptation. Moalem calls for using an evolutionary perspective to understand why the human body is not better designed, and why there are diseases in the first place. If we look at ancient living environments, he says, we can see if some diseases also function as defense mechanisms.
Courtesy of Walla
