[Science of Diabetes]
One of the most common questions asked by people with diabetes is: “What are normal blood sugar levels?” Unfortunately, there’s no simple answer to this question, because it depends on how you define normal.
It’s like deciding when someone is rich or poor, tall or short, thin or fat, or young or old. Most people would agree that a very skinny person was thin and a very fat person was fat. But how about the sizes in between? When does underweight become normal and when does normal become overweight? It’s all a matter of definitions and cutoff points set by one group or another.
The definitions of normal, prediabetes, and diabetes are usually made by august committees of diabetes experts, and they change from time to time. For example, not too long ago, it was decided that you’re diabetic if your fasting BG level is 126 mg/dL [to convert to mMol/L, divide by 18] or higher, instead of the previous cutoff of 140.
There are some guidelines about “nondiabetic” BG levels, for instance, “Nondiabetics never go over 140 mg/dL, no matter what they eat, and return to premeal levels in 2 or 3 hours” or “Nondiabetic fasting levels are 70 to 100 mg/dL.”
Textbooks that plot BG levels during the day in diabetic and nondiabetic individuals often show the nondiabetic levels as ranging from about 80 mg/dL before meals to close to 100 after some meals and about 120 after the largest meal of the day.
However, real life doesn’t always correspond to the textbooks. Some nondiabetic people, especially young, fit persons, keep their BG levels much more stable than that.
Many people with diabetes have used their home meters to measure their nondiabetic spouses and friends. Some find that the nondiabetic family members stay in the 80s no matter what they eat. Others find that some go up to well over 140 after carby meals. Were the ones who stayed in the 80s all day the true normals and the ones who went up to 120 or 160 really prediabetic or diabetic?
And how do nondiabetic BG levels fluctuate during the day when people are eating “normally” rather than in an institutional study setting or taking a glucose tolerance test?
European researchers have tried to answer this last question by studying 24 young (19 to 35 years) subjects they considered nondiabetic (fasting BG levels close to 80 mg/dL; body mass index from 19 to 25; A1c levels from 4.6 to 5.4; oral glucose tolerance tests well within normal limits, although at 1 hour some went up to only 110 and others went slightly over 160). They fitted them up with two different continuous glucose monitors and plotted their BG levels throughout the day on both an in-hospital fixed meal schedule and a “freeliving” meal schedule with fixed meal times but regular home food.
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