Infertility or reduced fertility is a common problem in the United States. According to the Centers for Disease Control and Prevention, nearly 1 out of 5 women are unable to get pregnant after a year of trying − the standard definition for infertility. 

Other common reproductive disorders that affect women include menstrual problems like irregular or heavy bleeding and a number of conditions such as uterine fibroids, endometriosis and sexually transmitted diseases.

When it comes to improving one's reproductive health, few things matter more than estrogen. 

What is estrogen?

Along with progesterone, "estrogen is one of two hormones secreted by the ovaries," says Andrew Greenberg, MD, director of the obesity and metabolism lab at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University. Hormones are chemical messengers that travel through the bloodstream to trigger specific functions or feelings throughout the body. 

Sometimes also called ovarian estrogen, the secretion of estrogen "begins around the time of puberty" and continues throughout reproductive life − "puberty to menopause," says Cynthia Stuenkel, MD, a clinical professor of medicine at UC San Diego School of Medicine. She explains that most women experience monthly cycling of estrogen and progesterone, "which matures the lining of the uterus in preparation for pregnancy should fertilization of the egg by a sperm occur." This ebb and tide of hormonal secretion by the ovary and monthly bleeding "becomes a familiar rhythm to most women," she adds. 

What is perimenopause?Experts explain the typical age and symptoms to expect.

Along with being secreted by the ovaries, the hormone is "produced in a female's adrenal glands and fat tissue," says Disha Narang, MD, an endocrinologist at Northwestern Medicine Lake Forest Hospital. And though significantly higher amounts of estrogen are produced and present in women, men also have the hormone as well. In males, estrogen is produced in the testes and, similar to women, in fat cells and adrenal glands. 

What does estrogen do?

In addition to its fundamental roles in reproductive health and menstrual cycle regulation, estrogen also affects the female urinary tract, reproductive tract, bones, breasts, skin, hair, mucous membranes, pelvic muscles and the brain, per Johns Hopkins Medicine.

Other important functions or benefits of estrogen include a reduced risk of cardiovascular disease before menopause, a reduced risk of developing abdominal obesity, and reduced vasomotor symptoms and genitourinary symptoms during perimenopause −"a period of time before women fully enter menopause," explains Greenberg.

In men, estrogen helps with sexual development, improved bone strength and muscle mass, and contributes to a healthy metabolism. 

What happens when estrogen levels are low?

Because estrogen plays so many vital roles in the body, it's important to maintain healthy levels of the hormone. In both males and females, low estrogen levels can affect "libido, cholesterol, metabolism, brain function, bone health and skin health," says Narang.

More:Have we been thinking about 'sex drive' all wrong?

To prevent low levels of estrogen production, good eating habits are a wise place to start since dietary choices significantly affect hormone balance. Reduced consumption of sugar-filled foods and getting plenty of foods high in fiber can help in this regard. Reducing one's stress through practices like mindfulness meditation and exercise can also be beneficial since high stress levels are associated with hormone imbalances. Quality and quantity of sleep is also important. 

If estrogen levels drop too low, one's physician may recommend estrogen supplementation or a form of estrogen therapy.