Irregular Menstrual Cycles
Definition and Clinical Presentation
The menstrual cycle is defined as the cyclic events that occur rhythmically during the reproductive period of a woman's life. Normal menstruation lasts 2 to 7 days and occurs every 21–35 days. Women are considered to have an irregular menstrual cycle if their cycle length is less than 21 days or more than 35 days, accompanied by less or very severe blood flow.
Between 14 and 25% of women experience irregular menstrual cycles, meaning their periods are heavier or lighter than usual, last longer than 35 days or shorter than 21 days, or they face other issues such as abdominal cramps. Menstrual irregularities also include bleeding or spotting between periods, bleeding or spotting after sex, menstrual cycle length varying by more than 7–9 days, and/or not having a period for 3–6 months. The prevalence of menstrual cycle irregularities among women ranges from 5% to 35.6%, depending on age, country of residence, and occupation.
Clinicians distinguish several subtypes of cycle disruption:
- Primary amenorrhea: A person has not started their period by age 16.
- Secondary amenorrhea: A person who has previously had periods stops having a period for more than three to six months.
- Oligomenorrhea: Infrequent cycles occurring at intervals greater than 35 days.
- Dysmenorrhea: A medical term for painful periods and severe menstrual cramps.
- Abnormal uterine bleeding: Bleeding between monthly periods, prolonged bleeding, or an extremely heavy period.
Body Systems Involved
The Hypothalamic–Pituitary–Ovarian (HPO) Axis
Menstrual cycle length and its rhythm are hormonally controlled by the functioning of the HPO axis. In the hypothalamus, the Kisspeptin–Neurokinin–Dynorphin (KNDy) neurons stimulate gonadotropin-releasing hormone (GnRH) secretion by GnRH neurons, which stimulate the anterior pituitary to secrete gonadotrophins — follicle-stimulating hormone (FSH) and luteinizing hormone (LH). In a normal menstrual cycle, the release of GnRH by the hypothalamus triggers the pituitary gland to release FSH and LH. Irregular periods can occur due to changes in the body's levels of estrogen and progesterone hormones, which disrupt the normal pattern of the period.
The Hypothalamic–Pituitary–Adrenal (HPA) Axis and Stress Response
Under stressful conditions, corticotrophin-releasing hormone (CRH) is released from the hypothalamus and stimulates adrenocorticotropic hormone (ACTH) from the pituitary gland; cortisol is then secreted from the adrenal gland. Cortisol inhibits the release of LH by the pituitary gland and estrogen by the ovaries, leading to interruption of the menstruation cycle. The underlying mechanism connecting stress to menstrual irregularities involves the HPG axis. Chronic stress can lead to the deactivation of the HPG axis, resulting in conditions like oligomenorrhea and secondary amenorrhea.
Thyroid System
Both hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) can impact the functioning of the reproductive system and lead to menstrual irregularities. The thyroid hormones thyroxine (T4) and triiodothyronine (T3) play an important role in regulating the menstrual cycle, and irregularities in their levels might result in irregular periods. Problems with other hormones located in the pituitary gland, such as TSH and prolactin, can cause menstrual irregularities.
Metabolic and Endocrine Systems
Insulin resistance and metabolic dysregulation can directly affect ovarian steroidogenesis by stimulating androgen production and impairing follicular development. Hyperinsulinemia may also reduce hepatic production of sex hormone-binding globulin, increasing circulating free androgens and contributing to ovulatory dysfunction. Chronic low-grade inflammation and oxidative stress associated with unhealthy dietary patterns may influence hypothalamic signalling and gonadotropin secretion, further disrupting menstrual cyclicity.
Contributing and Associated Factors
Polycystic Ovary Syndrome (PCOS)
Irregular periods can occur due to changes in the levels of the hormones progesterone and estrogen. Common causes include polycystic ovary syndrome (PCOS), birth control pills, breastfeeding, excessive exercise, intrauterine devices, hyperthyroidism, or hypothyroidism. One of the diagnostic criteria of PCOS is irregular or absent menstrual cycles. This makes fertility more challenging for some. High levels of androgens (hormones like testosterone) can also disrupt menstrual cycles in women with PCOS.
Body Weight and Composition
Dysmenorrhea, abnormal bleeding, irregular menstruation, and PMS were worsened by obesity (BMI >24.9) significantly. Excess calorie intake can influence menstrual disorders. Women affected by irregular menstrual cycles were found to be overweight or obese. Leptin (which is released from adipose tissue) has a role in the regulation of gonadotropins during puberty, pregnancy, and lactation and is considered an explanation for menstrual abnormality in obese women.
Energy Availability and Functional Hypothalamic Amenorrhea
Functional hypothalamic amenorrhea (FHA) is the absence of menstruation that results from low weight, excessive exercise, and/or stress. It is a diagnosis of exclusion and most commonly presents as a loss of menstruation. Exercise alone does not cause FHA; rather, it is the imbalance between energy intake and expenditure that leads to hypothalamic suppression, estrogen deficiency, and menstrual irregularities. FHA accounts for approximately 25% to 35% of all secondary amenorrhea and only 3% of primary amenorrhea.
Physicians recommend an energy availability threshold of 30 kcal/kg fat-free mass (FFM)/day to prevent FHA. Energy availability below this threshold can inhibit LH pulsation and cause menstrual disorders. To achieve menarche, there is a minimum fat storage requirement of 17%, whereas regular menses requires 22%. Runners, dancers, gymnasts, and figure skaters have a higher incidence of FHA due to the importance of leanness associated with success in these sports.
Psychological Stress
Chronic stress and anxiety are shown to alter hormone levels, leading to menstrual irregularities, including shortened or prolonged cycles and dysmenorrhea. Modifiable risk factors contributing to irregular menstruation include obesity, stress, and smoking.
Eating Disorders
Disorders like anorexia nervosa or bulimia can affect the reproductive system, ultimately leading to irregular periods. As eating disorders impact the body's nutritional status and hormonal balance, they might cause irregularities in the menstrual cycle. According to the American College of Obstetricians and Gynecologists, 16% to 47% of slender female athletes have disordered eating, which makes them at risk for functional hypothalamic amenorrhea.
Smoking
The increased use of hormone replacement therapy among smokers compared to non-smokers indicated that smoking induces a hypoestrogenic state. One mechanism through which smoking induces this state involves the increase in the level of HPA axis hormones, including adrenocorticotropic hormone, cortisol, and dehydroepiandrosterone, such as during stress.
Endometriosis and Structural Conditions
Endometriosis occurs when endometrial tissue grows outside of the uterus. The tissue often attaches itself to the ovaries or fallopian tubes. Endometriosis may cause abnormal bleeding, cramps, or severe pain before and during the period.
Associated Health Consequences
Menstrual irregularity has been found to be associated with various diseases and medical conditions, such as metabolic syndrome, coronary heart disease, type 2 diabetes mellitus, and rheumatoid arthritis. Anemia, osteoporosis, psychological problems, impaired quality of life, and infertility have also been recorded. Moreover, a significant correlation between irregular periods and the risk of developing pregnancy-related hypertensive disorders, as well as an increased risk of adverse obstetric and neonatal outcomes, has been demonstrated.
Nutrients Studied in Relation to Irregular Cycles
Vitamin D
Scientific Evidence: Vitamin D insufficiency correlates with irregular menstruation and PCOS risk. A randomized, placebo-controlled clinical trial investigated vitamin D and calcium as adjuvant therapy to metformin in PCOS patients. Forty PCOS women with 25-OH-vitamin D below 30 ng/mL were randomly assigned to take either metformin (1500 mg/daily) plus placebo or metformin (1500 mg/daily) plus calcium (1000 mg/daily) and vitamin D₃ (6000 IU/daily) orally for 8 weeks. An improvement in menstrual cycle irregularity was detected in 38.5% and 58.8% of patients in the metformin–placebo group and metformin–calcium–vitamin D group, respectively; the change was statistically significant only in the supplementation group (p = 0.002). Supplementation with natural molecules like inositol, vitamin E, vitamin D, and omega-3 may help alleviate pathological symptoms of PCOS, such as oocyte immaturity, insulin resistance, hyperandrogenism, oxidative stress, and inflammation. Evidence quality is moderate; existing trials are often small and involve vitamin D as one component of co-supplementation.
Inositol (Myo-Inositol and D-Chiro-Inositol)
Scientific Evidence: Natural molecules derived from herbal medicines and nutritional supplements, such as vitamin D, curcumin, CoQ10, N-acetylcysteine, and inositol, have been shown to play a therapeutic role in ameliorating inflammation and insulin sensitivity, restoring ovarian function, maintaining regular hormonal balance, and normalizing the menstrual cycle. Myo-inositol significantly improves insulin sensitivity (HOMA-IR SMD = −0.81) and SHBG levels (SMD = 9.65) by enhancing glucose transporter activity, according to an umbrella meta-analysis. Research shows inositol may help with some metabolic measures and potentially improve ovulation rates, but the evidence for significant clinical benefits remains limited. The 2023 International Evidence-Based PCOS Guidelines state that inositol can be considered based on individual preference. It appears to have limited harm but there is also limited strong evidence of meaningful improvements in ovulation, hirsutism, or weight loss.
Omega-3 Fatty Acids
Scientific Evidence: Omega-3 fatty acids ameliorate dyslipidemia (LDL-C SMD = −9.57; HDL-C SMD = 2.31) through anti-inflammatory mechanisms, according to umbrella meta-analysis data in PCOS populations. Considering the limited efficacy of omega-3 PUFAs in modulating hormone levels alone, the combination of vitamin E with omega-3 PUFAs or magnesium had an optimal effect on hormonal profiles, glycemic indices, HDL-C levels, and other biomarkers. Omega-3s might help lower insulin resistance, reduce triglycerides, and possibly decrease testosterone levels. The evidence quality seems moderate for metabolic benefits. Direct evidence for omega-3s normalizing cycle length per se remains limited.
Magnesium
Scientific Evidence: Nutrients considered especially important for menstrual disorders include iron, vitamin A, vitamin B complex, vitamin C, vitamin D, vitamin E, bioflavonoids, calcium, magnesium, fibre, and omega-3 fatty acids. Physical symptoms of PMS were significantly improved compared to placebo when women aged 15–45 diagnosed with PMS took 250 mg of magnesium or magnesium with 40 mg of vitamin B6 for 2 months. Co-supplementation of magnesium, zinc, calcium, and vitamins D or E can improve insulin sensitivity and CRP levels, lipid profiles, and glucose metabolism in women with PCOS. Evidence relates primarily to symptom severity in PMS and metabolic parameters in PCOS rather than direct restoration of cycle regularity.
Zinc
Scientific Evidence: Zinc deficiency can reduce zinc serum concentrations and consequently may cause glucocorticoid production to be irregular and lead to some neuropsychological symptoms such as irritability, depression, and emotional instability, along with being associated with dysmenorrhea. Consistent evidence from a systematic review suggests women with PMS-related emotional symptoms may benefit from zinc (≥30 mg/day) supplementation. Evidence for zinc's direct role in restoring cycle regularity as distinct from symptom relief is preliminary.
Iron
Scientific Evidence: Essential nutrients such as iron, magnesium, calcium, vitamin D, and omega-3 fatty acids are closely associated with menstrual health. Iron replenishes menstrual blood loss. A diet high in fiber can help regulate estrogen levels by promoting healthy digestion and excretion of excess hormones. Evidence linking iron supplementation directly to the restoration of cycle regularity is sparse; iron is most clearly indicated where heavy menstrual bleeding leads to deficiency.
B Vitamins (B6 and B12)
Scientific Evidence: Consistent evidence from a systematic review of randomized controlled trials suggests that women with PMS-related emotional symptoms may benefit from vitamin B6 (≥50 mg/day) supplementation. Long-term consumption of vitamin B6 supplements in high doses (>100 mg/day) has been associated with adverse side effects such as peripheral neuropathy; therefore intake for premenstrual symptom relief should be balanced with consideration of potential toxicity. Specific nutrients including vitamins B-12, inositol, vitamin D, E, and K, minerals such as calcium and selenium, and other compounds such as omega-3 fatty acids and probiotics have been highlighted for PCOS management.
Calcium
Scientific Evidence: Consistent evidence from a systematic review suggests women with PMS-related emotional symptoms may benefit from calcium (≥1000 mg/day) supplementation. There is only limited or no evidence to support the use of vitamin D, whole-grain carbohydrates, soy isoflavones, dietary fatty acids, or magnesium supplementation in isolation for PMS-specific diets. Evidence is stronger for PMS symptom reduction than for cycle length normalization.
N-Acetylcysteine (NAC)
Scientific Evidence: N-acetylcysteine has been shown to play a therapeutic role in ameliorating inflammation and insulin sensitivity, restoring ovarian function, maintaining regular hormonal balance, and normalizing the menstrual cycle in PCOS, with fewer side effects with clinical significance. Evidence in humans is preliminary and largely confined to PCOS populations.
Herbs Traditionally Used and Scientifically Studied
Vitex agnus-castus (Chasteberry)
Traditional Use: Vitex agnus-castus (VAC), the fruit of the sacred Vitex, also called chasteberry, chaste berry, or monk's pepper, has a long tradition in the treatment of menstrual cycle disorders.
Proposed Mechanism: The clinical pharmacological effects of VAC extract are not entirely clear, but are supposed to be due to a dopaminergic activity in the hypothalamic-pituitary–gonadal axis, leading to reduced prolactin secretion and potentially alleviating symptoms of PMS and associated mastalgia/mastodynia.
Scientific Evidence: Data from 1700 women with a mean age of 30.2 years were analyzed in a retrospective cohort study. The most common menstrual cycle disorders were dysmenorrhea (43.8%) and mastodynia/mastalgia (21.1%). Three-month treatment with VAC extract substantially decreased the percentage of patients with irregular cycle (from 9.1% to 0.1%). However, this was a retrospective observational cohort without a placebo control, which limits the conclusions that can be drawn. A meta-analysis of randomized controlled trials found that the consumption of Vitex did not have a significant effect on the amount of menstrual bleeding compared to the placebo group in trials assessing bleeding volume. A multicentric, open (non-placebo-controlled) study in 1634 PMS patients found that after a treatment period of three menstrual cycles, 93% of patients reported a decrease in the number of symptoms or even cessation of PMS complaints. Overall evidence for VAC in cycle regulation is promising but remains limited by the absence of large, rigorously blinded RCTs specifically targeting cycle length irregularity.
Cinnamon (Cinnamomum cassia / Cinnamomum verum)
Traditional Use: As one of the Chinese herbal medicines, cinnamon has the functions of tonifying fire, helping Yang, dispersing cold and relieving pain, and activating blood. As a common edible spice, it is considered to have anti-PCOS and anti-diabetes characteristics.
Scientific Evidence: Cinnamon can prevent insulin resistance caused by high-fructose diet, and many clinical trials have shown that cinnamon can improve metabolism by improving insulin resistance. A placebo-controlled, double-blind, randomized trial in 45 women evaluated cinnamon replacement therapy. The results showed that the menstrual cycle of the patients taking Cinnamomum cassia was more frequent than those taking placebo, and the improvement of the menstrual cycle was more obvious during the study period. It was proved that Cinnamomum cassia can significantly reduce fasting insulin and insulin resistance in PCOS patients. Evidence is preliminary; trials are small, and effects may be mediated primarily through insulin sensitization rather than direct hormonal action.
Dong Quai (Angelica sinensis)
Traditional Use: Also known as dang-gui in Traditional Chinese Medicine (TCM), dong quai is sometimes referred to as the female ginseng. In TCM, dong quai is often included in herbal combinations for abnormal menstruation, suppressed menstrual flow, dysmenorrhea, and uterine bleeding. Traditionally, dong quai is believed to have a balancing or "adaptogenic" effect on the female hormonal system.
Scientific Evidence: Contrary to the opinion of some authors, dong quai does not qualify as a phytoestrogen and does not appear to have any hormone-like actions in the body. The Natural Medicines Comprehensive Database concluded that dong quai is "possibly ineffective" for menopausal symptoms and that there is insufficient evidence to determine that it is effective for menstrual problems or PMS. Dong quai is one of the most commonly prescribed Chinese herbs for problems unique to women; despite the fact that it is known as a "female tonic" and is used by herbalists across the world for a variety of menstrual problems, little research has been done to show the safety and efficacy of dong quai. Overall, clinical evidence in humans for dong quai as a standalone intervention for irregular cycles is insufficient.
Shatavari (Asparagus racemosus)
Traditional Use: Shatavari is a traditional Ayurvedic herb widely used to support women's reproductive health. It is regarded as an adaptogenic and hormonal-modulating botanical, containing bioactive constituents such as steroidal saponins (shatavarins) that may help regulate hormonal balance and stress response. These botanical agents have been traditionally employed to address an array of reproductive health concerns, ranging from dysmenorrhea, PCOS, and infertility to the management of symptoms associated with pregnancy.
Scientific Evidence: Traditional use and emerging scientific evidence suggest that Shatavari may be beneficial in alleviating mood disturbances, fatigue, sleep problems, and stress-related symptoms commonly associated with PMS. Robust clinical evidence specifically demonstrating restoration of menstrual cycle regularity from Shatavari supplementation remains very limited, and large RCTs are lacking.
Ashwagandha (Withania somnifera)
Traditional Use: Ashwagandha has been traditionally employed in Ayurveda to address an array of reproductive health concerns, ranging from dysmenorrhea and PCOS to the management of menstrual irregularities.
Scientific Evidence: Ashwagandha's potential relevance to menstrual health is attributed largely to its adaptogenic, cortisol-lowering properties. Given that cortisol inhibits the release of LH by the pituitary gland and estrogen by the ovaries, leading to interruption of the menstruation cycle, interventions that moderate the stress response are biologically plausible. However, direct clinical evidence in humans linking ashwagandha supplementation to restoration of cycle regularity is currently limited and inconclusive.
Dietary and Lifestyle Factors
Overall Dietary Pattern
Lifestyle and nutritional factors can modulate hormonal processes and may contribute to inter-individual variability in menstrual patterns. Diets like the Mediterranean pattern, which emphasize fruits, vegetables, whole grains, and healthy fats, support menstrual balance, while high-glycemic diets and severe calorie restriction may disrupt cycles and trigger amenorrhea.
The whole grains present in the Mediterranean diet may play a role in reproductive health via their high content of dietary fiber, which can help regulate blood sugar levels, reduce inflammation, and promote the growth of desirable gut microbiota that are relevant to conditions such as PMS, menstrual irregularities, and PCOS. However, available evidence is very limited; there is some suggestion that higher adherence to the Mediterranean diet may be positively associated with a lower risk of early menarche and shorter menstrual cycles, but is unrelated to dysmenorrhea in one study.
Irregular menstruation, painful menstruation, and PMS were significantly associated with high intake of calories, proteins, carbohydrates, and total fat in a cross-sectional study, underscoring that dietary excess as well as restriction can be problematic.
Energy Availability
An energy deficit (which can occur independent of changes in body weight) appears to be the critical factor in both the weight loss and exercise-induced forms of FHA. Loucks and Thuma (2003) set the threshold for energy availability at 30 kcal/kg (in an acute setting), below which LH pulsatility is disrupted. The risk of menstrual disorders increases with a decrease in the caloric content of the diet and the duration of the energy deficit, and women with FHA have significantly lower energy availability.
Dietary Fiber
A diet high in fiber can help regulate estrogen levels by promoting healthy digestion and excretion of excess hormones. Dietary fiber also supports glycemic control and gut microbiota diversity, which are relevant to the metabolic features of PCOS-related cycle disruption.
Exercise
Exercise alone does not cause FHA; rather, it is the imbalance between energy intake and expenditure that leads to hypothalamic suppression, estrogen deficiency, and menstrual irregularities. Low energy availability resulting from high training volumes or intensities without adequate caloric intake plays a central role in disrupting the HPO axis. Moderate physical activity, in contrast, is associated with favorable metabolic outcomes in PCOS and does not carry the same risk profile.
Stress Management
Lifestyle factors like diet, sleep, and exercise mediate the relationship between mental health and menstrual irregularities, underscoring the need for holistic healthcare approaches. Following a healthy diet and managing stress have been reported as important factors in naturally preventing and managing menstrual-related symptoms, specifically through consumption of fresh, unprocessed foods and avoiding foods rich in refined carbohydrates.
Body Weight Maintenance
Insulin resistance and metabolic dysregulation can directly affect ovarian steroidogenesis by stimulating androgen production and impairing follicular development. Hyperinsulinemia may also reduce hepatic production of sex hormone-binding globulin, increasing circulating free androgens and contributing to ovulatory dysfunction. Both underweight and overweight states are associated with menstrual disruption through distinct but related mechanisms involving leptin, adiponectin, and sex hormone regulation.
Smoking and Alcohol
Modifiable risk factors contributing to irregular menstruation include obesity, stress, and smoking. As described above, smoking is associated with a hypoestrogenic state that can contribute to cycle disruption, and the BMC Women's Health literature indicates that the association between alcohol consumption and menstrual cycle irregularity has also been a subject of investigation, though evidence requires further elucidation.
References
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