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 Dr. 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, Dr. 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, Dr. 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, Dr. 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,” Dr. 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 Dr. 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.