Experts in women's health now refer to a "window of opportunity" in regards to when to start menopausal hormone therapy (MHT). The consensus is that hormones are best started around the time of entering menopause. For some women, this may mean they are in the late stages of perimenopause when cycles become more infrequent. Estrogen has a protective effect on blood vessels and the heart. When estrogen falls after menopause, this protection declines. Restoring estrogen needs to happen before changes to the blood vessels occur. Once ten years has passed since the last menstrual period, it is not recommended to initiate hormone therapy. If estrogen is added to blood vessels that have signs of damage, it can produce more harm then benefit and increase the risk of heart attacks and stroke.
Once hormone therapy is started, there is some evidence to suggest that stopping it prematurely before the age of 60 can increase heart disease risk, reiterating that there is no need to stop MHT after five years of therapy as was thought in the early 2000's.