What causes irregular periods?

Irregular periods — cycles that vary significantly in length, frequency, or heaviness — can be driven by hormonal imbalance (including thyroid dysfunction, hyperprolactinaemia, and elevated androgens), polycystic ovary syndrome (PCOS), perimenopause, significant weight changes (too high or too low), intense exercise, chronic stress, eating disorders, and certain medications. In adolescence, irregular cycles are common as the HPA axis matures. Persistent irregularity, very heavy bleeding, or cycles shorter than 21 or longer than 35 days warrant medical assessment.

How does stress affect the menstrual cycle?

Chronic stress activates the HPA axis, elevating cortisol and suppressing GnRH (gonadotropin-releasing hormone) production from the hypothalamus. GnRH is essential for triggering LH and FSH release from the pituitary, which drive ovulation. When stress is prolonged or severe, this suppression can cause anovulatory cycles (cycles without ovulation), irregular timing, or in extreme cases, amenorrhoea (cessation of periods). This is a physiological protective mechanism — the body downregulates reproductive function when resources are insufficient for pregnancy.

What nutritional factors support menstrual regularity?

Iron — depleted by heavy periods — needs to be replenished to support energy and healthy menstrual function. Adequate dietary fat and caloric sufficiency are essential (very low fat diets and undereating suppress ovarian function). Zinc supports progesterone production. Vitamin B6 supports hormone metabolism. Magnesium regulates prostaglandins that influence cramping. Omega-3 fatty acids have anti-inflammatory effects on the endometrium. Seed cycling (consuming specific seeds in different menstrual phases) is popular but lacks robust clinical evidence — though it promotes fibre, zinc, and lignin intake.

When should irregular periods be investigated by a doctor?

Medical assessment is recommended for: periods that are absent for three or more months (amenorrhoea) in someone not pregnant or menopausal; very heavy periods (soaking through a pad or tampon every hour for two or more hours, or passing clots larger than a 50p coin); cycles consistently shorter than 21 or longer than 45 days; significant pain; periods that were regular and have become irregular without obvious cause; or irregular periods alongside other symptoms suggesting thyroid dysfunction, PCOS, or other hormonal conditions.

Hormonalmoderate Risk

Menstrual Irregularities and PMS

Menstrual irregularities and PMS are common conditions affecting hormonal balance and daily life

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Reviewed by Dr. Ian Henderson · Microbiobial Health & Medicine26 March 2026Emerging evidence

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Menstrual irregularities and PMS are common conditions affecting hormonal balance and daily life

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People with menstrual irregularities and PMS may experience irregular cycles, mood swings, and physical discomfort

What is Menstrual Irregularities and PMS?

Menstrual irregularities and PMS are common conditions that can impact daily life and overall well-being. A holistic approach considers the interconnectedness of body, mind, and spirit to manage symptoms and promote hormonal balance.

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Overview

Symptoms & Affected Systems

Contributing Factors

Supporting Lifestyle Strategies

Evidence Context

When to Seek Professional Help

Related Conditions

Hormonal Imbalance

Thyroid Imbalance

Reactive Hypoglycaemia

Type 2 Diabetes

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