How Your Period Can Affect Your Blood Sugar
Many of the premenstrual symptoms you associate with your period, such as depression, irritability, bloating, and cravings, are caused by hormonal fluctuations. It’s helpful to understand how your period affects your blood sugar and devise strategies to avoid blood sugar spikes and drops.
Do Periods Raise Blood Sugar or Lower It?
Whether periods raise or lower blood sugar (glucose) depends on the menstrual cycle phase. Hormone levels and insulin sensitivity change daily and sometimes throughout the day. While there may be trends in insulin sensitivity and blood glucose levels, there are no hard and fast guidelines.
A typical menstrual cycle lasts 28 days, starting with the first day of your period, with ovulation at approximately day 14 and menstruation (period) at days 1–5, unless conception occurs. Menstrual cycles vary from 21 to 35 days from month to month. Most variations in length occur in the follicular phase of the menstrual cycle.
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Four key hormones regulate the menstrual cycle:
- Luteinizing hormone (LH) surges trigger an egg’s release from the ovary.
- Follicle stimulating hormone (FSH) matures the ovarian follicle that releases the egg.
- Estrogen thickens the uterine lining.
- Progesterone prepares the uterus for a fertilized egg and supports early pregnancy.
The menstrual cycle can be divided into phases, depending on which hormone is dominant. In each phase, your hormone levels and blood sugar may trend up or down.
Key phases of the menstrual cycle:
- Menses phase, days 1–5: Menses is when the inner lining of the uterus is shed. This phase typically lasts five days but can last 2 to 7 days. Progesterone and estrogen levels are low.
- Follicular phase, days 6-14: After the uterine lining is shed, specialized cells in the ovary, called the granulosa and theca cells, release estrogen. Rising estrogen levels stimulate the uterus to begin rebuilding to prepare for a potentially fertilized egg implanting in the uterus. Estrogen levels are rising, and progesterone levels remain low.
- Ovulation days 11-14: A burst of LH in response to increasing estrogen causes the egg to be released from the dominant follicle, travel down the fallopian tube, and, if fertilized, implant in the uterus. Estrogen levels are high, and progesterone levels remain low. FSH and LH peak right before ovulation. Higher FSH seems to improve insulin sensitivity.1,2 Higher LH reduces insulin sensitivity. You may notice higher blood sugars around ovulation from decreased insulin sensitivity due to spiking LH.
- Luteal phase days 15-28: Once ovulation occurs, the dominant follicle becomes an endocrine organ called a corpus luteum and begins producing progesterone. Initially, there is a decline in estrogen followed by a second peak just before menses. When the corpus luteum breaks down, progesterone levels decline. This decline triggers the shedding of the uterine lining and menses.3 Many women notice their blood sugar increasing right before their period starts. This is because of higher progesterone levels, relative to estrogen.
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