This post is the second in a series of my Walk with a Doc Talks. Click here for my talk on The Other Benefits of Exercise.
There are two basic forms of diabetes mellitus: type 1 and type 2.
In the past Type 1 Diabetes (DM1) was known as Juvenile Diabetes, or Insulin-Dependent Diabetes. It is caused by an injury (often auto-immune) to the pancreas, which is a long, thin glandular organ that senses blood sugar and produces insulin and glucagon appropriately. Insulin is the hormone that opens cells to allow blood sugar in, which all cells, regardless of type, use for energy. Glucagon is the hormone that raises a low blood sugar. You will recognize glucagon by the nauseous, cranky, headachy feeling it gives you right before lunch, or in the middle of the afternoon.
Type 2 Diabetes (DM2), formerly known as NIDDM, is the type we see most often in adults, and now even in obese teenagers and children. In DM2 the body still makes both insulin and glucagon, but the body’s cells are resistant to it. It’s like a key trying to fit into a lock. The lock sticks, so you try more and more keys until finally, you can slide the key into the lock. The key (insulin) never changed, but the lock won’t work. Similarly, as your blood sugar goes up, your body produces more and more insulin, but the cells won’t open to let the sugar in. The level of sugar in the blood rises and rises, while the cells are starving. These effects are why DM causes the triad of hunger, increased urination, and thirst (from needing more water to make more urine). For the sake of the rest of this discussion, I am going to talk exclusively about preventing DM2.
So how do I prevent diabetes?
Our risk of DM2 goes up with age. Likewise, genetics plays a part: Native Americans, Pacific Islanders, African Americans and Hispanics have the highest risk. We cannot change either our heritage or our age. But the strongest predictor of DM2 risk is weight. 90% of those with DM2 are overweight (BMI 25.0-29.9) or obese (BMI >=30). We all know how easy it is for the pounds to creep on, but taking them off is harder.
A landmark study that followed more than fifty thousand women for more than 6 years found a remarkable correlation between watching TV and the risk of obesity and DM2. In 1997, the average American woman watched 34 hours of TV per week, or almost 5 hours a day. Women who watched two hours of TV a day were 23% more likely to become obese, and 14% of the TV watchers developed DM2.
Interestingly, it seems that the sitting wasn’t the only harmful effect of the TV. Sitting for a similar time span at work increases DM risk by only 7% (and obesity risk by 5%). Contrast that with those women who were moderately active around the house for two hours during the day. Their risk of diabetes decreased over those six years by 12%, and their risk of obesity decreased by 9%.
Okay, TV bad. Walking around at home, good. But what happens if we add in walking for exercise?
A brisk 1 hour walk each day decreased obesity risk by 24% and decreased diabetes risk by 34%. The study authors estimated that if Americans decreased TV watching to <10hrs/week and began walking 30 minutes/day, we could prevent 30% of new DM cases. We could also decrease the incidence of obesity in this country by 43%.
Other studies have also tried to prevent the development of DM2 in at-risk adults by giving medicine. The Diabetes Prevention Project recruited men and women with pre-diabetes (45% of whom were in high-risk ethnic groups) and gave them medication or help with weight loss and exercise. Medication had a small effect in preventing diabetes but was less effective than diet and exercise that led to weight loss. At the end of the study, those who made lifestyle changes (including improved eating and 150 minutes of brisk walking each week), decreased their 5-year risk of developing diabetes by 58%. They didn’t have to hit their ideal weight to decrease their risk, either. The lifestyle changes resulted in a very modest weight loss (5-7 % over 16 weeks).
That’s right: medication was less effective than exercise. That 150 minutes of brisk walking a week is 30 minutes a day for 5 days. Or 25 minutes 6 days a week. At a weight of 160lbs, a 5% weight loss is 8 pounds. At 200 lbs, a 5% loss is 10 lbs. We’re not talking about the Biggest Loser here, just a gradual, sensible change in habits, including TV, exercise and food that can cut your risk of diabetes in half.
For more information, the CDC has a state-by-state list of organizations offering the Diabetes Prevention Program curriculum.
Television Watching and Other Sedentary Behaviors in Relation to Risk of Obesity and Type 2 Diabetes Mellitus in Women. Frank B. Hu, MD, PhD; Tricia Y. Li, MD; Graham A. Colditz, MD, DrPH; Walter C. Willett, MD, DePH; JoAnn E. Manson, MD, DrPH. JAMA. 2003; 289(14):1785-1791.
Diabetes Prevention Program (DPP) Research Group. The Diabetes Prevention Program (FPP): description of lifestyle intervention. Diabetes Care. 2002; 25(12):2165-2171.
This was a transcript of my Walk with a Doc talk from April. Here is my talk on the other benefits of exercise. Next month I’ll post my talk on how much exercise is “enough”.