Final answer:
An increase in estrogen activity during pregnancy or post-menopausal replacement therapy raises levels of various substances which can affect bone density, the cardiovascular system, and risk of certain types of cancer. Hormone Therapy (HT) is used to mitigate some of these effects but carries associated risks.
Step-by-step explanation:
An increase in estrogen activity, such as during pregnancy or with post-menopausal replacement therapy, raises levels of several substances and presents various physiological changes. During pregnancy, estrogen levels climb markedly, supporting the fetal development and preparing the female body for childbirth. For post-menopausal women, hormone therapy (HT) can help alleviate symptoms of menopause such as hot flashes and vaginal dryness but also carries risks such as increased chances of certain types of cancer.
After menopause, lower amounts of estrogens can lead to conditions like osteoporosis due to decreased bone density and cardiovascular disease due to less cholesterol-managing effects of estrogen. To address these risks, HT is sometimes administered to increase estrogen levels, which can help maintain bone density and manage menopausal symptoms. Nonetheless, there is an ongoing debate regarding the benefits and risks of such therapies, especially after findings from the Women's Health Initiative.