Menstrual Phase Impacts Exercise Effects in Type 1 Diabetes

Heidi Splete

July 05, 2022

Women with type 1 diabetes may need additional glucose after exercise during the luteal phase of the menstrual cycle, compared with other times, according to a study in nine women.

"We know that exercise is very beneficial for people with type 1 diabetes; we also know that fear of hypoglycemia is a major barrier to exercise in this population," said Jane E. Yardley, PhD, in a presentation at the annual scientific sessions of the American Diabetes Association, New Orleans. Women with type 1 diabetes (T1D) perceive more barriers, compared with men, she added.

The menstrual cycle could be an additional barrier to exercise for women with T1D because it increases glucose fluctuations that have not been well documented in the literature to date, said Yardley, of the University of Alberta, Augustana.

The follicular phase of the menstrual cycle lasts from menses to the midcycle, about 14 days later. This is followed by the luteal phase, which lasts until approximately day 28, Yardley explained. Data on insulin sensitivity have shown that the late luteal phase is associated with "a little less insulin sensitivity" in women with T1D, she noted.

To assess the relationship between menstrual cycle, glucose control, and exercise, Yardley and colleagues compared the effects of a moderate aerobic exercise on glycemic responses between the early follicular and late luteal phases of the menstrual cycle in nine female participants with T1D.

The exercise involved 45 minutes of aerobic cycling at 50% of predetermined peak oxygen uptake (VO2peak) for 45 min. The mean age of the participants was 30.2 years, the mean hemoglobin A1C was 7.4%, and the mean VO2peak was 32.5 mL/kg per min. The women reported regular menstrual cycles, and none were using oral contraceptives.

Blood samples were collected before and immediately after exercise and after an hour of recovery. Participants wore continuous glucose monitors for at least 1 hour before and after exercise.

Menstrual cycle was confirmed via estrogen, estradiol, and progesterone.

Insulin levels varied greatly among the study participants, but the differences were not significant, Yardley said. Glucose levels consistently decreased during exercise and increased after exercise, she noted.

No significant difference in glucose was observed between the follicular and luteal phases.

However, "this needs to be interpreted in the context of the safety profiles that are in place in our lab," which include carbohydrate supplements for individuals whose blood glucose levels drop below 4.5 mmol/L, she said.

In the current study, 6 of 9 participants required additional carbohydrates during the luteal phase, but only 1 participant needed additional carbohydrates during the follicular phase, she noted. For this reason, no differences were noted. "We actually prevented changes," she said.

No significant differences were noted in mean glucose levels or number of hypoglycemic episodes at any of the time points between the two phases.

"One place where we did see a difference was in hyperglycemia 24 hours after exercise," Yardley said. Level 1 hyperglycemia 24 hours after exercise was significantly more frequent in the follicular phase, compared with the luteal phase (P = .028).

The study findings were limited by the small sample size and homogenous population, and more research is needed to interpret the data, said Yardley.

However, the need for more glucose supplementation to prevent hypoglycemia during the luteal phase suggests a higher hypoglycemic risk associated with aerobic exercise during this time, she said.

In addition, the results suggest that the menstrual cycle should be taken into consideration when female participants are involved in exercise studies, she noted.

Study Supports Personalized Exercise Plans

"It is important to evaluate effects of exercise in people with type 1 diabetes and evaluate whether there is a difference those effects in men and women," said Helena W. Rodbard, MD, an endocrinologist in private practice in Rockville, Md., in an interview. "There is also a need to evaluate to what extent the changes in blood glucose patterns in women in response to exercise differ depending on the phase of the ovarian cycle," said Rodbard, who was not involved in the study.

In the current study, "the researchers observed a decline in glucose during a 45-minute period of moderate aerobic exercise, cycling at 50% VO2peak followed by an increase during a 60-minute recovery period. There was a suggestive finding, in the nine subjects, that more carbohydrate supplementation was needed during the late luteal phase of the menstrual cycle than during the follicular phase," Rodbard noted. "In contrast, the authors reported a significantly increased degree of hyperglycemia during the recovery phase for subjects during the follicular phase. These findings are consistent with and extend several recent studies from Yardley and coworkers, who have been focused on this area of research," she said.

"This study provides provocative evidence that glucose responses to aerobic exercise in women may depend on the timing in relationship to their ovarian cycle," said Rodbard. "These findings are based on a small group of subjects and were present in some but not all subjects. Clinicians should encourage women to evaluate and record their experiences during and after exercise in terms of need for carbohydrate supplementation for documented or symptomatic hypoglycemia and in terms of glucose changes as recorded using continuous glucose monitoring (CGM), both in relation to type of exercise and in relation to time in the menstrual cycle," she said.

The findings also highlight the importance of individualized therapy that is "based on subjective inputs combined with analysis of CGM data during and following exercise," said Rodbard. "It is likely that use of Automated Insulin Delivery (AID) will be helpful in achieving this level of individualization in view of the wide range of types, intensity, and duration of physical activity and exercise in which people with T1D engage and the myriad factors that can influence the glycemic response," she said.

Looking ahead, "the authors and others should expand the present series of subjects using aerobic exercise and examine other types of exercise as well," Rodbard noted. "It will be important to evaluate the consistency of these changes in glucose patterns within individuals on multiple occasions, and it would be helpful to repeat the studies in women using oral contraceptives."

Yardley disclosed research support from Abbott, Dexcom, and LifeScan and disclosed serving on the speaker's bureau for Abbott Diabetes. Rodbard had no financial conflicts to disclose. She 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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