People With Diabetes Felt Better the Day After Their Blood Sugar Wobbled

I always took it for granted that the flattest blood-sugar line was the best one. Peaks were bad, valleys were bad, and the gold star of diabetes care was a calm horizontal stripe across the app. So I read the result presented in Milan at this year’s European Association for the Study of Diabetes meeting twice before I believed it. In people with diabetes, a day when glucose bounced around more than usual was followed by a better next day, not a worse one.

Keep one condition in mind the whole way through. The bouncing happened while glucose stayed largely within a healthy range, and the study’s own summary says outright that this is no argument for poor control. What the researchers found is subtler than “let it rip,” and I think it says more about the daily work of diabetes than it does about glucose.

The data come from PRO-MENTAL, a study run by Dominic Ehrmann and colleagues at the Research Institute Diabetes Academy Mergentheim in Germany. They followed 400 adults with diabetes, 72 percent of them with type 1, for 14 consecutive days. Each day participants scored their wellbeing on a short five-item questionnaire built from the WHO-5, and a continuous glucose monitor logged their sugar around the clock. The team then lined up the two records and asked whether yesterday’s glucose predicted how someone felt today, after adjusting for age, sex, diabetes type and how good the previous day had felt. That last adjustment takes the edge off the lazy explanation that cheerful people simply stay cheerful.

Two glucose patterns predicted a better tomorrow. The first is the one you’d guess. More time in the normal range, which the study set at a tight 70 to 140 mg/dL, came with higher next-day wellbeing, a beta of 0.32 with P = .035, according to Healio’s report on the abstract. The second is the one I can’t stop poking at. Higher-than-usual variability, measured as the coefficient of variation (the statistic for how much the line jumps), also predicted a better next day, with a beta of 0.12 and P = .003, which made it the statistically firmer of the two signals. Time spent high or low the day before didn’t predict next-day wellbeing in either direction.

So wait, why would a jumpier line leave anyone feeling better? Biologically it sounds backwards. I sat with it for a while before it clicked for me that the glucose trace may be the wrong thing to stare at, because what it records, indirectly, is effort. The authors suggest that people who push hardest to iron out every fluctuation may be paying for it in burden and restriction, and that the cost shows up as a worse quality of life.

Think about what the flattest line takes. You pre-bolus and wait for the insulin to catch before you eat. You skip the dessert or the second helping or the drink with a friend, because your phone already shows you what it’ll do to the curve twenty minutes out. You chase a small rise with a correction, then chase the low that the correction caused. Nobody’s pancreas produces a line that flat by itself; a person builds it by overriding their own day, meal after meal. Ehrmann sees that person in clinic: “In our clinic, we see people with diabetes who are overly focused on avoiding any type of glucose fluctuation.” The warning that follows is blunt: “Too strict glucose management with the goal to avoid fluctuations has the potential to negatively affect quality of life.”

Ehrmann’s other line is one I found almost tender: “Glucose fluctuations, when within normal ranges, should be seen as a part of normal life.” Your body would agree. After a meal the gut pours glucose into your blood, the pancreas answers with insulin, muscle and liver pull the sugar out of circulation, and the line settles. On a walk, working muscle draws it down. Overnight the liver trickles glucose back out so your brain never runs dry. A healthy metabolism rises and falls all day, which makes a perfectly flat line on an app an engineering target, not the biological norm.

Look at where that engineering target is being sold now. In March 2024 the FDA cleared the first over-the-counter continuous glucose monitor, Dexcom’s Stelo, for adults who don’t use insulin. The agency explicitly included “those without diabetes who want to better understand how diet and exercise may impact blood sugar levels,” and said people could buy one “without the involvement of a health care provider.” The graph has jumped the fence from medical tool to consumer screen. My read is that a green, in-range, flat-as-a-ruler graph makes a beautiful product precisely because you can always fall a little short of it. Ehrmann names the same drift inside the field: “We tend to overly focus on the glucose side of diabetes and establish higher and higher goals.” To be fair, Ehrmann also notes that those goals can motivate people, especially on automated insulin delivery, and says the field needs to understand what targets and constant glucose visibility do to how patients feel. The question is coming from inside diabetes research. The only funder named for PRO-MENTAL is the German Center for Diabetes Research (DZD), and Ehrmann reports no relevant financial disclosures.

Now the brakes, quickly. This is an oral conference abstract (number 43), not a peer-reviewed paper, so the full methods could still shift. The effects are small and observational, and nobody has shown that the swings cause the good days. Sleep quality and energy also predicted next-day wellbeing, so glucose is one instrument in a bigger band. The study’s bar for “normal” was strict, too: its normal window topped out at 140 mg/dL, while its own above-range cutoff sat at 180 mg/dL, the line most time-in-range targets use. None of that flips the direction of the signal. Even under that tight definition, within-range wobble turned up on the good-day side of the ledger.

I came in sure that steadier was always kinder, and I’m leaving with that certainty dented. If I wore a sensor, I’d keep working on time in range, because that finding held up. I wouldn’t treat every bump as a failure to correct, though. I’d let a good dinner show up on the graph and leave the phone in my pocket.

Sources

1. ScienceDaily: Diabetes study finds keeping blood sugar too steady may come at a price
2. Healio: Greater glycemic variability linked to improved next-day quality of life in diabetes
3. News-Medical: Stricter glucose control may affect quality of life in people living with diabetes
4. FDA: FDA clears first over-the-counter continuous glucose monitor