Many women notice that their glucose levels change throughout the month, and that these changes are related to their periods. Understanding what happens during the menstrual cycle can help explain these changes.
At the beginning of a cycle, a small gland in the brain called the pituitary gland makes a hormone. This tells the ovaries to make estrogen, and to prepare an egg in the ovary for possible pregnancy. About halfway through the cycle at about day 14, the pituitary gland makes a different hormone. This one tells the ovary to release one of the mature eggs for possible fertilization. After release of an egg (called ovulation), the ovaries start tomake another hormone called progesterone.
The estrogen makes the lining of the uterus become thicker. The progesterone matures this thickened lining. If a sperm fertilizes the egg, the fertilized egg can attach to the lining of the uterus and grow into an embryo. If there is no fertilized egg, the ovary stops making progesterone after fourteen days. Without progesterone the lining of the uterus dies and is expelled during the period. Then the process starts again.
So, what does this have to with blood sugar? It turns out that progesterone, and to a lesser extent, estrogen, can affect blood sugar levels. Progesterone increases the amount of insulin that is needed to lower blood sugar levels. For people taking insulin, it means they have to take more insulin to keep the sugars under control. On top of that, progesterone can cause breast tenderness, bloating, cravings and mood changes that are common features of PMS (premenstrual syndrome). Those cravings can alter food choices that can further affect blood sugars. Once progesterone levels fall and the period starts, blood sugar levels improve and insulin doses can be reduced.
The message for people taking insulin is be prepared to take more insulin in the latter half of the cycle. Once the period starts, be prepared to take less to avoid a low blood sugar. Knowing what is happening and being able to predict what will come, will take the mystery out of blood sugar cycles that accompany menstrual cycles.
About the author
Alice Cheng
Alice Cheng is an endocrinologist at Trillium Health Partners and Unity Health Toronto. She is an Associate Professor at the University of Toronto and co-host of the podcast series, Diabetes Care on Air.
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