Exercise of Any Type Boosts Type 1 Diabetes Time in Range

Heidi Splete

June 16, 2022

Adults with type 1 diabetes had significantly better glycemic control on days they exercised, regardless of exercise type, compared to days when they were inactive, according to a prospective study in nearly 500 individuals.

Different types of exercise, such as aerobic workouts, interval training, or resistance training, may have different immediate glycemic effects in adults with type 1 diabetes (T1D), but the impact of exercise type on the percentage of time diabetes patients maintain glucose in the 70-180 mg/dL range on days when they are active vs. inactive has not been well studied, Zoey Li said in a presentation at the annual scientific sessions of the American Diabetes Association.

In the Type 1 Diabetes Exercise Initiative (T1DEXI) study, Ms. Li and colleagues examined continuous glucose monitoring (CGM) data from 497 adults with T1D. The observational study included self-referred adults aged 18 years and older who had been living with T1D for at least 2 years. Participants were assigned to programs of aerobic exercise (defined as a target heart rate of 70%-80% of age-predicted maximum), interval exercise (defined as an interval heart rate of 80%-90% of age-predicted maximum), or resistance exercise (defined as muscle group fatigue after three sets of eight repetitions).

Participants completed the workouts at home via 30-minute videos at least six times over the 4-week study period. The study design involved an activity goal of at least 150 minutes per week, including the videos and self-reported usual activity, such as walking. The data were collected through an app designed for the study, a heart rate monitor, and a CGM.

The researchers compared glucose levels on days when the participants reported being active compared to days when they were sedentary. The goal of the study was to assess the effect of exercise type on time spent with glucose in the range of 70-180 mg/dL, defined as time in range (TIR).

The mean age of the participants was 37 years; 89% were White. The mean duration of diabetes was 18 years, and the mean hemoglobin A1c was 6.6%. "An astounding 95% were current continuous glucose monitoring [CGM] users," said Ms. Li, a statistician at the Jaeb Center for Health Research in Tampa, Fla.

A total of 398 participants reported at least one exercise day and one sedentary day, for a total of 1,302 exercise days and 2,470 sedentary days.

Overall, the mean TIR was significantly higher on exercise days compared to sedentary days (75% vs. 70%, P < .001). The median time above 180 mg/dL also was significantly lower on exercise days compared to sedentary days (17% vs. 23%, P < .001), and mean glucose levels were 10 mg/dL lower on exercise days (145 mg/dL vs. 155 mg/dL)

"This all came with a slight hit to their time below range," Ms. Li noted. The median time below 70 mg/dL was 1.1% on exercise days compared to 0.4% on sedentary days (P < .001). The percentage of days with hypoglycemic events was higher on exercise days compared to sedentary days (47% vs. 40%, P < .001), as they are related to time below 70 mg/dL, she added.

The differences for mean glucose level and TIR between exercise days and sedentary days were significant for each of the three exercise types, Ms. Li said.

"After establishing these glycemic trends, we looked at whether there were any factors that influenced the glycemic differences on exercise vs. sedentary days," Ms. Li said.

Regardless of exercise type, age, sex, baseline A1c, diabetes duration, body mass index, insulin modality, CGM use, and percentage of time below range in the past 24 hours, there was higher TIR and higher hypoglycemia on exercise days compared to sedentary days.

Although the study was limited in part by the observational design, "with these data, we can better understand the glycemic benefits and disadvantages of exercise in adults with type 1 diabetes," Ms. Li said.

Don't Forget the Negative Effects of Exercise

"It is well known that the three types of exercise can modulate glucose levels. This can be very useful when attempting to reduce excessively high glucose levels, and when encouraging people to engage in frequent, regular, and consistent physical activity and exercise for general cardiovascular pulmonary and musculoskeletal health," Helena W. Rodbard, MD, an endocrinologist in private practice in Rockville, Md., said in an interview.

"However, it was not known what effects various types of exercise would have on time in range (70-180 mg/dL) and time below range (< 70 mg/dL) measured over a full 24-hour period in people with type 1 diabetes," said Rodbard, who was not involved with the study.

"I was surprised to see that the effect of the three different types of exercise were so similar," Rodbard noted. "There had been previous reports suggesting that the time course of glucose could be different for these three types of exercise."

The current study confirms prior knowledge that exercise can help reduce blood glucose, and increase TIR, said Rodbard. The study shows that TIR increases by roughly 5-7 percentage points (about 1 hour per day) and reduces mean glucose by 9-13 mg/dL irrespective of the three types of exercise," she said. "There was a suggestion that the risk of increasing hypoglycemia below 70 mg/dL was less likely for resistance exercise than for the interval or aerobic types of exercise," she noted.

As for additional research, "This study did not address the various ways in which one can mitigate the potentially deleterious effects of exercise, specifically with reference to rates of hypoglycemia, even mild symptomatic biochemical hypoglycemia," said Rodbard. "Since the actual amount of time below 70 mg/dL is usually so small (0.3%-0.7% of the 1,440 minutes in the day, or about 5-10 minutes per day on average), it is difficult to measure and there is considerable variability between different people," she emphasized. "Finding optimal and robust ways to achieve consistency in the reduction of glucose, between days within subjects, and between subjects, will need further examination of various types of protocols for diet, exercise and insulin administration, and of various methods for education of the patient," she said.

The study was supported in part by the Leona M. and Harry B. Helmsley Charitable Trust. Ms. Li and Rodbard had no financial conflicts to disclose. Rodbard serves on the editorial advisory board of Clinical Endocrinology News.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.


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