Several hormones from the hypothalamus and pituitary glands in the brain and the ovaries regulate the menstrual cycle. This regulatory system is called the HPO axis. The hypothalamus secretes gonadotropin-releasing hormone (GnRH) that causes the pituitary to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH and FSH stimulate ovarian production of the female sex hormones estradiol and progesterone, and the development and release of a mature egg, or ovulation. Many things can affect coordination of the HPO axis and cause menstrual irregularities, such as an early period or mid-cycle bleeding. Intense exercise might be a factor in early periods, although this is not typical.
Exercise and Menstrual Irregularity
Exercise benefits the body in many ways, and moderate physical activity is unlikely to cause menstrual irregularity. Intense exercise, however, might affect the menstrual cycle regulation by suppressing hormones in the HPO axis. This can develop during vigorous exercise combined with low energy availability, or burning more calories than are consumed. When this occurs, the body conserves energy by inhibiting nonessential functions, such as the menstrual cycle. For example, female athletes with menstrual irregularities often exhibit reduced release of LH. Disruption of the HPO axis often begins with irregular menstrual cycles, including early periods, and may progress to infrequent periods or complete cessation of menstruation. Exercise-related menstrual irregularities occur primarily in women involved in long-term, intense physical training.
Other Causes of an Early Period
An occasional early period is quite common and considered normal. Menstrual irregularity, including early periods, occurs commonly in teenagers and women over 40 due to hormone imbalances during these menstrual transition years. Certain medical conditions, including hypothyroidism or a high level of the hormone prolactin, might also result in early periods. This pituitary hormone is normally present in low levels in both men and women. Levels normally increase during pregnancy and breastfeeding. Abnormally elevated prolactin levels can occur as a side effect of certain medications and with medical conditions, such as a pituitary tumor, or severe liver or kidney disease.
In some cases, what seems to be an early period might actually represent mid-cycle bleeding. Mid-cycle bleeding can be caused by use of oral contraceptives, uterine fibroids, cervical polyps, or cancer or infection of the reproductive tract. During the first weeks of pregnancy, some women mistake implantation bleeding -- when an embryo implants into the lining of the uterus -- for an early period.
Additional Ways Exercise Affects Your Period
Intense exercise, such as that typically done by competitive or elite recreational female athletes, is more likely to cause less frequent periods and absence of periods than early periods. Menstrual abnormalities associated with intense exercise commonly occur as part of the female athlete triad, a set of three conditions found in some elite female athletes. These conditions include low energy availability, menstrual cycle abnormalities, and decreased bone mineral density or osteoporosis. A review article published in the September 2013 issue of the "Mayo Clinic Proceedings" reported that 23.5 percent of high school and collegiate female athletes experience menstrual abnormalities. The authors also noted that as a runner's training mileage increases from less than 8 to more than 70 miles per week, the incidence of absent periods for more than 3 months increased from 3 percent to 60 percent.
When to Seek Medical Care
Consult with your doctor before beginning any new exercise program. An occasional early or irregular period is common and typically doesn't indicate a significant medical problem. However, if your periods are frequently irregular -- including being early or late, or not occurring for several months -- see your doctor to determine the cause. If exercise is a factor in your menstrual irregularity, your doctor might suggest moderating your exercise program, increasing your caloric intake, or both.
See your doctor as soon as possible if you suspect you might be pregnant, or you experience irregular periods accompanied by potential warning signs, including: -- Abdominal or pelvic pain. -- Nausea or vomiting. -- Copious, malodorous or unusual vaginal discharge. -- Heavy or prolonged bleeding.
Reviewed by: Tina M. St. John, M.D.