The causes of diabetes are complex and only partly understood. Complicating the picture even further is the fact that there are multiple types, each with its own risk factors. Type 1 and Type 2 diabetes are the most common, encompassing about 97% or more of cases in the U.S. Each results from a combination of environmental and genetic influences.
Of those, Type 2 is far and away the most common, about 90% of cases.
Obesity is thought to be a major contributor to Type 2 diabetes. Being overweight is a good prototype for a cause since it is itself a combination of genetic background and lifestyle choices. Though the diet opted for and the amount of exercise one chooses to undertake are lifestyle choices, it’s still true that some individuals gain or shed weight more easily than others.
But there are many other factors, as well.
A history of diabetes during pregnancy contributes to part of the total risk. Just shy of 40% of women who develop diabetes during pregnancy (a type known as gestational diabetes) will later develop Type 2 diabetes. That typically occurs within 5-10 years after giving birth. Those who give birth to larger babies have a greater risk.
Glucose intolerance is another genetically influenced factor. Since Type 2 diabetes results not from underproduction of insulin (as in Type 1) but from inadequate use of it, it shouldn’t be surprising that glucose intolerance is a contributing circumstance. That glucose intolerance should exist is puzzling enough, since it’s a major source of the body’s energy. But genetic anomalies produce some unusual situations.
Ethnicity plays a role in whether or not an individual will develop Type 2 diabetes, though the reasons are not fully understood. Even after adjusting for lifestyle, Aboriginals, Africans, Latin Americans and some Asian groups are at higher risk. The profile varies between 1.5-2 times the incidence among Caucasians, according to one broad Canadian study. Oddly, though, the risk of Type 1 diabetes is much higher among Caucasians than any other race.
Having high blood pressure raises the odds, too. That again is partly a lifestyle (chiefly, diet and exercise) choice but it has a strong genetic aspect as well. There’s a strong correlation between those with high blood pressure and those who will develop diabetes. Similarly, high cholesterol levels increase the risk. Over 40% of those with diabetes have higher than average levels of cholesterol in the blood.
But simple family medical circumstance is probably the largest genetic risk factor.
An individual with a parent or sibling who has Type 1 diabetes has him or herself a risk 10-20 times higher than average. For a newborn baby with a parent who has Type 1 diabetes the odds are 1 in 25, or 4% if the mother gives birth before age 25. Over age 25, the risk is 1%, about the same as the general population. The odds rise again to about 10% if either parent contracted diabetes before age 11.
The genetic risk factors of contracting diabetes are still an active area of research. Fortunately, while in generations past there was nothing one could do to influence them, modern genetic treatments hold out promise of altering even these odds.