On the first days of your cycle, the loss of blood combined with lower levels of the hormone progesterone can lead to muscle fatigue. (8fit.com)
In fact, a 2008 study found that couples who reported any kind of marital intimacy — everything from holding hands to sex — exhibited lower levels of a hormone produced by stress. (health.com)
In one study, women with depressive symptoms in the first two weeks after delivery had lower levels of the hormone oxytocin in the third trimester than women without depression. (sciencenews.org)