Even the experts didn’t know. Until now.
Tomorrow, the American Medical Association’s professional journal, JAMA, will publish a systematic review and meta-analysis of previously published studies. Each of those studies was at least 12 weeks long and randomized and controlled clinical trials. Meeting these criteria were 47 trials that included 8,538 people.
Daniel Umpierre of the Hospital de Clinicas de Porto Alegre, Brazil, and eight colleagues call their meta-analysis “Physical Activity Advice Only or Structured Exercise Training and Association With HBA1c Levels in Type 2 Diabetes.” JAMA made the full-text of the meta-analysis available to me under embargo until this afternoon, and the abstract is online.
As the title of the meta-analysis indicates, the researchers compared structured exercise with a control group of people who were just told to get exercise. As you might expect, words were not enough.
But the researchers went further. They looked at the effects of structured aerobic exercise, structured resistance training, and both of them combined, comparing all three forms with the control group.
Each form of exercise reduced A1C levels. Now, some of the differences here surprised me.
Remember that the A1C measures how much glucose in percent is stuck to the blood circulating in our bodies. When we reduce our level from, say, 7.0 to 6.0, we have brought it down by 1.0 percent. If a diabetes medication can help us achieve that much reduction in a few months, medical professionals are pleased.
Overall, the 23 studies of structured exercise led to an A1C reduction of 0.67 percent. Structured aerobic exercise made the most difference, 0.73 percent, rather more than the 0.57 difference from structured resistance training. I still don’t understand why combining these two forms only reduced A1C by 0.51 percent, but that’s what the meta-analysis found.
Those studies included different amounts of exercise. The researchers found the biggest differences by comparing studies of more than 150 minutes per week with studies of less exercise. When people with diabetes exercised more than 150 minutes per week in the studies, they averaged a 0.89 percent drop in A1c. But those who exercised less than 150 minutes in their studies had only a 0.36 percent reduction.
The word “structured” that the meta-analysis researchers used bothered me. Personally, I am no great fan of structure of any sort. More than most people, I don’t like to be told what to do.
But the researchers have a good reason here to stress structure. They define it as “planned, individualized, and supervised.” In the context of the study, those elements are necessary to make sure that what they were measuring was real. In real life, we can do without the supervision. But we can’t do without pushing ourselves to get the exercise we need to control our diabetes.