The Highs (and Lows) of Estrogen
It is probably more accurate to say that low levels of progesterone, combined with elevated levels of estrogen, appear to cause many PMS symptoms. The body functions well when estrogen and progesterone are in proper balance, but when that balance is compromised, as it can be during the luteal phase (the second half) of a typical menstrual cycle, a woman will experience side effects of the imbalance.
Studies have shown that if estrogen exceeds a normal estrogen/ progesterone ratio, PMS symptoms increase. For example, estrogen interferes with the body’s thyroid function, while progesterone enhances it.
Cells in the body depend on hormones secreted by the thyroid gland to regulate their metabolism, and poor thyroid function decreases the body's ability to use carbohydrates, fats, and proteins. So, high estrogen levels inhibit thyroid hormone levels, which, in turn, cause cravings and increased appetite because the body is not effectively using food. Low thyroid levels can also cause depression, weakness, and fatigue.
The thyroid, one of the larger endocrine glands in the body, regulates the body’s metabolism (or how fast it burns energy). The thyroid is connected to reproductive function, and that connection be tighter in women than in men. Women may be more vulnerable to thyroid impairment, predisposing them to rapid mood cycles.
Similarly, research has shown that estrogen intensifies the effect of aldosterone, a hormone that helps regulate levels of sodium and potassium in the body. In contrast, progesterone blocks the effects of aldosterone, so high estrogen levels, combined with low progesterone levels, lead to fluid retention or bloating.
Too much estrogen in the body also decreases endorphin levels in the brain, causing depression and anxiety. Endorphins are the feel-good chemicals in the brain that regulate or elevate mood. Studies have shown that women with PMS commonly have low endorphin levels.