What Causes PMS?

Experts say that the definitive cause of PMS is not yet known. However, the most likely explanation for PMS is that many women are sensitive to the hormonal shifts that occur in the second half of the menstrual cycle.

What Hormones Cause PMS?

PMS most often occurs in women with normal menstrual cycles. During the normal menstrual cycle, the ovaries make two main hormones, called estrogen and progesterone. Estrogen is made by the ovaries throughout the entire menstrual cycle. It reaches its highest levels during the second and third weeks and declines during the last week. During the last two weeks of the cycle the ovaries also make progesterone. The last two weeks of the menstrual cycle is called the luteal (secretory) phase.

Both estrogen and progesterone prepare the uterus (womb) to accept a fertilized egg. Both estrogen and progesterone also affect women's moods.

How Do Hormonal Changes Cause PMS?

The exact cause of PMS is still not known, but researchers believe that PMS symptoms occur because progesterone and estrogen cause changes in brain chemicals called neurotransmitters. The most likely neurotransmitters affected are:

• Serotonin: Women with PMS have fluctuations in serotonin levels. These changes may cause depression and carbohydrate cravings. Serotonin is made by the body from the amino acid tryptophan.

• GABA: GABA stands for gamma-aminobutyric acid. This neurotransmitter is important in feeling calm.

• Endorphins: Endorphins are important in the experience of pain and pleasure. Estrogen and progesterone change endorphin levels.

• Norepinephrine: Norepinephrine and epinephrine are also neurotransmitters that influence mood. In addition, these substances play a role in blood pressure and heart rate.

Could Calcium And Magnesium Imbalances Be Involved?

Some researchers think that certain imbalances in calcium and magnesium levels may trigger PMS symptoms. These two minerals affect nerve cell communication and blood vessel opening and closing. These functions may be involved in PMS symptoms.

Does Stress Cause PMS?

No. PMS is not caused by stress. Women may experience more stress prior to menstruation, and they may handle stress differently during this time, but it is not the cause of PMS. Excessive stress can, however, make PMS symptoms worse.