The Twin Epidemics of Obesity and Type 2 Diabetes: Definitions and Such
Over the next few entries I will discuss, in some detail (as promised) what have been widely-described in the lay press as “epidemics” of both childhood obesity and diabetes. I will try to answer 3 basic questions: first, how do we define obesity and diabetes, and are these conditions really epidemic?; second, assuming the answer to the first question is “yes,” why are we having these problems?; and third, what can we do about it?
Definitions
First, obesity as a medical condition, is generally defined based on “body mass index,” or BMI. This is a rough measure of one’s weight relative to height and has been widely used to relate weight to health outcomes. It is far from perfect (for example, muscular teens may have high BMIs but look reasonably lean and mean) but is a simple way to get an idea of one’s health risks related to their weight. In adults, BMI can be calculated by dividing the weight in kilograms (weight in pounds divided by 2.2) by the height in meters squared (height in inches X 0.0254). It’s easy with a calculator, but even easier if you understand the metric system, which is very nice. The height should be without shoes and the weight, with only light clothing. For example, a person who is 5 foot 9 inches tall and weighs 180 pounds has a BMI of about 27. Another person who is 5 foot 5 inches tall and weighs 150 pounds has a BMI of about 25. By definition, a BMI in the range 18.5-24.9 is considered healthy; <18.5 is considered underweight; 25-29.9 is considered overweight; and anything higher is considered obesity (levels 35 and higher have even more scary terms to describe them). It is important to know that these BMI definitions are not used in children since BMIs change with linear growth and age. Most experts use special charts constructed by the Centers for Disease Control (CDC) and define overweight as BMI greater than the 80 or 85th percentile for age; greater than 95th percentile roughly corresponds to an adult BMI of 30 or greater. Most experts advise against using the term "obesity" when referring to children who are overweight, I guess, to avoid hurting someone's feelings?- go ahead and call the grown-ups obese if you want to. The Ugly Statistics
Based on BMI data, many many children in the U.Ss and their parents are overweight. Recent data suggest that more than 60% of adults are overweight or obese, and roughly 40% of children are above the 85th percentile and 25% above the 95th percentile (of course, based on statistics, only 5% of children should have BMIs above the 95th percentile). No matter how we look at the data, the majority of adults in the U.S. are overweight, and many children are too. Of course, it can be tricky using normative data to define a disorder, such as overweight or obesity. One could argue that we should define new norms based on current population BMIs. That argument is not a very good one though because the current definitions of overweight and obesity are based (mostly) on health care outcomes. For example, what are the long-term health risks associated with a BMI of 32 vs. 23? Answer: greater.
Trends
Whatever BMI cutoffs one uses, there has been a dramatic increase in overweight/obesity in adults and in children. The increase has been relentless over the past 30 years, but dramatically greater over the past 10-20 years. It is unclear if things have leveled off over the past 2-3 years (The CDC would not like that as it might have a negative impact on their funding to fight obesity-that’s maybe not a very fair comment by me?). As we will discuss later, the consequences of obesity (from now on I’ll use that term as a general one, to include all degrees of overweight, from pleasantly plump to who knows what) are very serious, both to the health of the individual, and the health of our economy.
What Does This Have To Do With Diabetes?
I haven’t really said a word about diabetes yet. Type 2 diabetes is a medical condition characterized by high blood sugar (glucose) levels and risks for serious complications of the eyes, kidneys, nerves, heart, and blood vessels. This condition is typically genetically-based but does not generally occur unless the individual is overweight. So, what would you guess has happened to the prevalence (frequency) of diabetes during our obesity epidemic? You guessed it- more and more diabetes, paralleling the increase in obesity. Recent data suggest the prevalence of diabetes in the U.S is just under 10% with much higher levels in certain ethnic groups (Blacks, Hispanics, Pacific Islanders, Native Americans, etc.). In people over 60, the prevalence is more than 20%. This is all quite extraordinary. We are even seeing quite a bit of type 2 diabetes in children now; this disorder used to be almost exclusively an adult disorder. Now, some pediatric diabetes centers are reporting that 20% or more of their children with newly-diagnosed diabetes have the type 2 variety (they are all quite a bit overweight, as you would expect). I agree that we are seeing more type 2 diabetes in children in association with more overweight, but I believe the condition is being way overdiagnosed- I don’t doubt that it’s diabetes, but in many cases it’s typical type 1 diabetes (what children usually get) and overweight, not type 2 diabetes and overweight. In my experience, cases of type 2 diabetes in childhood rarely occur before the teen years, even in the face of considerable overweight. It happens, but not a often as news report would suggest. We’ll come back to this issue later- it’s not so important for our current discussion.