The menstrual cycle is a carefully regulated sequence of events that prepares the female body for a potential pregnancy. It starts with the follicular phase, which includes menstruation and the maturation of the ovarian follicle. This is followed by ovulation (mature follicle releases egg) and then by the luteal phase (during which the egg moves through fallopian tubes); if pregnancy doesn’t occur, then the cycle re-starts again with the follicular phase and menstruation.^[1]

These events are primarily driven by hormonal communication between the brain (specifically, the hypothalamus and pituitary gland) and the female reproductive system, collectively called the hypothalamic-pituitary-ovarian (HPO) axis.^[2] The first menstruation (menarche) occurs around age 12 (median; range of 10-16), and reoccurs regularly every 24 to 38 days,^[3] stopping at menopause (near age 50), which signifies the end of reproductive fertility. The menstrual cycle also stops during pregnancy and often during lactation.^[4]

The menstrual cycle is an important component of overall health. As such, the menstrual cycle is considered a vital sign by some clinicians.^[5] There are a variety of ways to measure menstrual cycle health, ranging from simple, at-home tracking methods to bloodwork and ultrasound imaging. A basic assessment of the menstrual cycle starts with measurements of frequency (menstruation or bleeding occurs every 24 to 38 days), regularity (the number of days between menstruation is similar each month), duration (bleeding does not last longer than eight days), and volume (loss of no more than 80 mL of menstrual blood per cycle).^[6] The phases of the menstrual cycle are sometimes measured via basal body temperature and hormone levels in saliva, urine, or blood.^[1] If there are abnormalities, like infrequent menstruation (oligomenorrhea), too frequent menstruation (polymenorrhea), the total absence of menstruation (amenorrhea), or very heavy bleeding (menorrhagia), a clinician can perform additional assessments to better understand the underlying cause of the abnormality.

These additional assessments may include bloodwork and imaging. Blood tests can detect the levels of different hormones that affect the menstrual cycle (e.g., progesterone, estrogen, thyroid hormone, androgens, prolactin). They can also measure iron levels, which are sometimes affected by menstrual bleeding, and may aid in the diagnosis of underlying bleeding disorders or infections. In some cases, imaging of the reproductive system is also necessary, usually beginning with an ultrasound. Serial transvaginal ultrasounds can visualize the changes that occur in the ovaries and endometrial lining throughout the menstrual cycle.^[7]

Regular exercise may alleviate pain and other negative symptoms before and during menstruation.^[8][9][10] Regular exercise can also shorten the length of menses.^[11]

Conversely, too much exercise can be detrimental to menstrual cycle health, causing menstrual irregularities or even the total absence of menstruation.^[12][13] This is not a normal response to exercise and should be evaluated by a clinician. It may be a sign of relative energy deficiency in sport (RED-S), a condition indicating that the body does not have enough energy to meet its demands.^[14] The consequences of RED-S are far-reaching, serious, and potentially irreparable.^[15][16]

Supplements for the menstrual cycle are often studied in the context of correcting deficiencies and/or reducing the symptoms of conditions like premenstrual syndrome, endometriosis, dysmenorrhea, and polycystic ovary syndrome. For example, vitamin D deficiency is associated with dysmenorrhea and abnormal menstrual bleeding patterns, in which case supplementing with vitamin D to correct the deficiency could be beneficial.^[17][18] Additional supplements that might improve menstrual-related symptoms (with varying levels of efficacy) include chaste tree, magnesium, vitamin B6 and B₁, ginger, calcium, selenium, omega-3 fatty acids, curcumin, and inositol.^{[19][20][21][22][23][24][18]}

Another supplement that is often studied in menstruating people is iron because blood loss via menstruation can reduce iron levels in the body, especially if the bleeding is heavy.^[17] Iron may also be lost during exercise.^[25] Because iron is used to make red blood cells, a deficiency in iron can lead to anemia, which means that the blood cannot carry enough oxygen throughout the body. Iron supplementation is an effective treatment for iron deficiency.^[26][27]

Before beginning any supplements, it is important for menstrual-related symptoms to be evaluated by a clinician. Some supplements, like iron, can cause damage if excessive amounts accumulate in the body. Such accumulation is rarely the result of excessive oral intake and is instead secondary to other underlying medical problems, both congenital and acquired. ^[28]

Eating a nutritious diet with an appropriate amount of kilocalories is integral to menstrual cycle health. Dietary patterns that include a diversity of fruits and vegetables, dairy products, fish, green tea, and plant-derived compounds and avoid excessive intakes of alcohol, red and processed meats, and caffeine are correlated with fewer menstrual-related disorders.^[29][30][31] There are also associations (but no robust data) between a more “proinflammatory” dietary pattern and reduced levels of sex hormone binding globulin, which might affect menstrual-related symptoms in some people.^[32]

Diet is also implicated in the timing of menarche (or the first menses). Menstruation requires energy, so malnourishment and low body weight can result in a later onset of menarche, whereas overnutrition and obesity are associated with an earlier age at menarche.^[33][34][35]

The menstrual cycle is affected by numerous internal and external factors, all of which can alter the cycle’s length, regularity, and symptoms. Some of these factors are not modifiable, such as race/ethnicity, age, intrauterine exposures, family history, adverse childhood events, and genetics.^[36][37] Other factors are related to the environment, like exposure to air pollution, endocrine-disrupting chemicals, and certain viruses and bacteria, as well as the geographic climate.^[36][38] There are also important personal and lifestyle factors to consider, including mental health,^[39][40], sleep health,^[41][42] body mass index,^[43][44][45] use of tobacco and cannabis,^[46][43] lactation,^[47][48] use of contraceptives (oral medications, intrauterine devices, ect.),^[49][50] shift work,^[37] and possibly even a history of concussions.^[51]

Of these factors, psychological stress is a common target for interventions aimed at restoring normal menses, reducing menstrual-related symptoms, and improving fertility. For example, acupuncture and acupressure may help some people with premenstrual syndrome or menstrual irregularity.^[52][53] Psychosocial interventions, particularly cognitive behavioral therapy and mindfulness-based therapies, may increase pregnancy rates in people with infertility^[54] and improve mood in people with premenstrual syndrome.^[55][56]