The ovaries contain a finite number of follicles, which are established before birth. Over a woman's reproductive lifetime, this follicular reserve progressively declines. By the time a woman reaches her late 40s, the remaining follicles become increasingly resistant to follicle-stimulating hormone (FSH), leading to irregular ovulation and fluctuating estrogen levels that characterize perimenopause. The North American Menopause Society provides extensive clinical resources on managing this transition.
As estrogen production diminishes, the body's thermoregulatory center in the hypothalamus becomes more sensitive to temperature changes, narrowing the thermoneutral zone. This is why even slight body temperature increases can trigger vasomotor symptoms like hot flashes and night sweats, which affect up to 80% of women during the menopausal transition.
The decline in estrogen also disrupts the balance of neurotransmitters including serotonin and norepinephrine, which regulate mood, sleep, and cognitive function. This neurochemical shift explains why menopause affects far more than reproductive health, influencing everything from bone density to cardiovascular protection. Many women also experience weight gain during this transition due to shifting metabolic and hormonal dynamics.
