The menstrual phase: what is actually happening in your body and how to support it

The menstrual phase is the part of your cycle most women know best by feel and least well by biology. You bleed for three to seven days. What is rarely explained is what is happening underneath. The menstrual phase is a specific hormonal state with specific effects on your nervous system, immune system and nutrient needs. Understanding those mechanics turns the period from something to push through into something to support. This guide covers the biology, the evidence on period pain and endometriosis, plus the iron story.

What is the menstrual phase?

The menstrual phase is the first phase of the menstrual cycle. Day 1 of bleeding is Day 1 of the cycle. Bleeding usually lasts three to seven days. The cycle as a whole runs roughly 24 to 35 days from one Day 1 to the next.^[1]

One of the most common misunderstandings is treating the period as a separate event. The cycle is not the period. The period is the opening phase of the cycle. The follicular phase rises out of it. Ovulation happens in the middle. The luteal phase brings things back down. Then the next period begins.

The bleeding itself is the body shedding the uterine lining that was built up during the previous cycle to support a possible pregnancy. When pregnancy did not occur, hormone levels fall. The lining is no longer supported. It releases.

A cycle that is regular for you within the 24 to 35 day window, with bleeding under seven days that does not soak through a pad or tampon every one to two hours, is generally considered healthy. Very short, very long or absent cycles are signals worth investigating with a doctor.^[2]

Which hormones are at play during your period?

Four hormones drive the menstrual cycle: estrogen, progesterone, follicle-stimulating hormone (FSH) and luteinising hormone (LH). Estrogen and progesterone are made by the ovaries. FSH and LH are brain signals that tell the ovaries what to do.

During the menstrual phase, estrogen and progesterone are at their lowest point in the entire cycle. This is the hormonal floor. The high progesterone of the previous luteal phase has dropped. Estrogen has not yet started to climb again. The body reads this drop as the signal to release the unused uterine lining.

The mechanism behind the bleeding is prostaglandins. These signalling molecules are produced in larger quantities by the endometrium when estrogen and progesterone fall. Prostaglandins make the uterine muscle contract so the lining can shed. They also restrict blood flow to the uterine wall. That combination of contraction and reduced blood flow drives cramping. It is the physiological basis of primary dysmenorrhea, the medical name for period pain in the absence of underlying disease.^[3]

FSH starts to rise toward the end of menstruation as the brain signals the ovaries to begin maturing the next batch of follicles. The hormonal floor is already tilting upward by the time bleeding stops.

Why does the menstrual phase often feel hard?

The cultural shorthand says women are emotional because their hormones are high. The biology says the opposite during menstruation. Estrogen and progesterone are at their lowest. Pain perception, mood stability, sleep and the inflammatory response are all operating without the usual estrogen cushion.

What that often looks like in practice:

• Lower energy. Especially on days one and two when bleeding is heaviest.
• Higher pain sensitivity. Low estrogen means a smaller buffer against prostaglandin-driven cramps and headaches.
• Emotional openness. The same nervous system that feels cramps more sharply also processes emotion more sharply.
• Brain fog. Sleep is often less restorative. Iron stores may be lower. Both feed cognitive sluggishness.
• A pull toward rest. The body is doing real physiological work. Wanting to slow down is biology, not weakness.

None of these signals are pathological on their own. Recognising the pattern is the first step toward working with it instead of against it.

Period pain: common, but not normal

Up to nine in ten women of reproductive age experience some menstrual pain. Roughly one in five describe it as severe enough to interfere with daily life or schooling. Period pain is the most common gynaecological complaint in young women. It is also one of the most underdiagnosed, often dismissed as something to live with.^[3][4]

Common does not mean normal. Mild discomfort that responds to a hot water bottle and an ibuprofen is one thing. Pain that makes you call in sick. Pain that makes you nauseous or faint. Pain that does not respond to over-the-counter painkillers. These are signals the system is out of balance or that something underlying needs investigating.

The biology of primary dysmenorrhea is well understood. Excess prostaglandins drive uterine hypercontractility. Blood flow is restricted. Tissue becomes briefly hypoxic. Pain receptors fire. NSAIDs work because they block prostaglandin production. They are first-line treatment. Hormonal contraception is second-line because it suppresses the cycling that drives the prostaglandin surge.^[5]

Nutrition matters too. Magnesium has been studied across small randomised trials in primary dysmenorrhea with most reporting reduced pain scores compared to placebo.^[6] A 2020 meta-analysis also found women with dysmenorrhea were two and a half times more likely to develop chronic pain conditions later. Period pain may be a marker of broader pain processing patterns worth taking seriously.^[4]

If your period pain is severe, recurrent or worsening, the right move is a medical workup.

When is it more than period pain? Endometriosis

Endometriosis is a chronic inflammatory disease in which tissue similar to the uterine lining grows outside the uterus. It can settle on the ovaries, the fallopian tubes, the bowel and other pelvic structures. This tissue still responds to cyclical hormones. It thickens. It bleeds. It cannot exit the body. The result is inflammation, scar tissue and often severe pain.^[7]

Endometriosis affects roughly one in ten women of reproductive age. Diagnostic delay averages four to eleven years from symptom onset. Symptoms include severe period pain that does not respond to standard treatment, pain during sex, pain on urination during menstruation, chronic pelvic pain outside the period, fatigue and infertility.^[7][8]

The 2022 European Society of Human Reproduction and Embryology (ESHRE) guideline updated the diagnostic pathway. Imaging through transvaginal ultrasound or MRI by an experienced operator is now sufficient for many suspected cases. Laparoscopy is no longer required before treatment can begin. Earlier symptom investigation matters more than ever.^[9]

A clear note on what nutrition can and cannot do. No supplement and no diet heals endometriosis. Hormonal therapies are often essential to slow disease progression and protect fertility. Surgery may be necessary. Nutrition supports the body. It does not replace medical care. If you have symptoms of endometriosis or persistent severe period pain, speak with a doctor. Earlier diagnosis changes outcomes.

Iron loss during menstruation: the standout nutrient story

Iron is the most consequential nutrient story of the menstrual phase. Each period involves average blood loss of 30 to 60 ml. That carries roughly 0.5 to 1 mg of iron out on top of the 1 mg lost daily through sweat and stool. Across a decade of cycles without sufficient replacement, this is the leading cause of iron deficiency in women.^[11]

Iron deficiency is the most common nutrient deficiency worldwide. Women of reproductive age are affected at roughly ten times the rate of men. Up to two-thirds of women with heavy bleeding develop iron deficiency. Many go undiagnosed for years.^[11][12]

Iron deficiency vs iron deficiency anaemia

Iron deficiency comes first. Iron deficiency anaemia comes later. The body draws on stored iron, measured as ferritin, before haemoglobin starts to fall. By the time haemoglobin shows up as low, iron stores have often been depleted for months. Symptoms of iron deficiency without anaemia include fatigue, brain fog, breathlessness on stairs, hair thinning, restless legs, brittle nails and headaches. These often get attributed to stress or workload long before iron is investigated.^[12]

Ferritin: the marker that matters

Iron stores are best assessed through serum ferritin. The standard laboratory cutoff is often listed as below 15 micrograms per litre, set by the World Health Organization based on older data. A 2021 NHANES analysis in The Lancet Haematology found that iron-deficient erythropoiesis actually begins around a ferritin of 25 micrograms per litre in non-pregnant women.^[13] A Cochrane review confirmed that 30 micrograms per litre is more clinically informative for identifying iron deficiency in people with symptoms.^[14] A ferritin of 16 might be flagged as normal on a lab report. It is not. Many clinicians in women's health now aim for ferritin in the 30 to 50 microgram per litre range as a functional target.

Iron forms and absorption

Not all iron supplements are equal. Ferrous sulfate is the most commonly prescribed form. It is cheap and poorly tolerated, with high rates of nausea, constipation and reflux that lead many women to stop supplementing.^[15]

Iron bisglycinate is iron bound to two glycine molecules. The chelated form is absorbed differently from inorganic iron salts and is consistently better tolerated. A 2025 comparative study found ferrous bisglycinate raised haemoglobin without increasing colonic inflammatory markers. Ferrous sulfate did. Human data on bisglycinate similarly show good repletion at lower doses with fewer gut side effects.^[15]

Iron benefits from being paired with vitamin C. Ascorbic acid converts non-heme iron to its more absorbable form. Recent research also suggests taking iron every other day may improve fractional absorption by giving the iron-blocking hormone hepcidin time to fall between doses.^[16]

How to support the menstrual phase

Supporting the menstrual phase is not about doing more. It is about doing the right things at the right intensity. The body is asking for replacement of what is being lost and a slightly gentler pace while it does the work.

Nutrition

Your plate during menstruation needs to cover four bases. Protein supports hormone production and stable blood sugar. Complex carbohydrates support energy and serotonin synthesis. Healthy fats support absorption of fat-soluble vitamins. Micronutrient density matters more than usual, with particular attention to iron, vitamin C, B vitamins and magnesium.

Iron-rich foods to prioritise include red meat, organ meats, oysters, lentils, beans, tofu, pumpkin seeds and dark leafy greens. Pair plant iron sources with vitamin C from peppers, citrus or berries. Coffee and tea inhibit iron absorption when consumed with meals. A thirty-minute gap fixes that.

Movement

Current evidence does not support the idea that women must avoid exercise during menstruation. Strength and endurance are not significantly impaired by the menstrual phase in well-designed studies. What does change is perceived effort. Many women feel best with reduced intensity on heavy days. Some feel fine training as usual. Both are valid.

Recovery

Sleep is often less efficient around menstruation. Cortisol can be more reactive. Prioritising the sleep environment and reducing low-value stress matters more than usual. The nervous system is already operating with less hormonal cushioning.

Targeted nutrients to consider

• Iron as bisglycinate. 15 to 20 mg during bleeding days is a reasonable replacement target. Higher doses for diagnosed deficiency belong with a clinician.
• Vitamin C. Pair with iron to improve absorption.
• Magnesium. Useful for cramp tolerance and sleep. Bisglycinate or citrate forms are best tolerated.
• Vitamin B6. Supports neurotransmitter and hormone metabolism.
• Folate with vitamin B12. Essential for healthy red blood cell production. Often low alongside iron in women with heavy periods.
• Alpha-lipoic acid. An antioxidant studied for mitochondrial function and inflammation balance.

What this means for nōuxx Bloody Berry

nōuxx Bloody Berry is the menstrual phase formula in the nōuxx Cycle Routine. It is built around the priorities above. Iron as bisglycinate at a replacement dose. Vitamin C for absorption. B vitamins including B6, folate and B12 for red blood cell production. Magnesium in a bioavailable form. nōuxx Bloody Berry does not replace medical care or food. It removes the friction of figuring out what to take during the days your body needs the most support.

Common questions

Is period pain normal?

Mild pain that responds to a hot water bottle or a single dose of ibuprofen is common. Severe pain that interferes with daily life or does not respond to over-the-counter treatment is not normal. It is worth investigating with a doctor.

How much iron do I lose during my period?

Most women lose 30 to 60 ml of blood per period, which represents roughly 0.5 to 1 mg of iron on top of the 1 mg lost through daily routes. Women with heavy bleeding can lose substantially more.

What is ferritin and what level should I aim for?

Ferritin is your iron storage protein measured through a blood test. Many labs flag deficiency only below 15 micrograms per litre. Recent evidence suggests iron-deficient erythropoiesis begins around 25 micrograms per litre in women. A practical functional target many clinicians work toward is 30 to 50, especially when symptoms are present.

Can I exercise during my period?

Yes. Studies do not show meaningful impairment of strength or endurance during the menstrual phase. Many women prefer lower-intensity training on the heaviest days. Listen to how your body responds.

What helps period cramps?

NSAIDs like ibuprofen are first-line because they block prostaglandin production. Heat helps. Magnesium has reasonable supporting evidence at modest doses. Hormonal contraception is used for severe cases. If pain persists, see a doctor.

Should I take iron every day?

Iron is stored in the body and can be overdosed. Daily preventative supplementation without a blood test is not advised for most women. A common evidence-based approach is replacement-dose iron during the bleeding days only. For diagnosed deficiency, your doctor may recommend a higher dose given every other day for better absorption.

When should I see a doctor about my period?

If you soak through a pad or tampon every one to two hours. If your period lasts longer than seven days. If cycles are absent or wildly irregular. If pain is severe or worsening. If you bleed between periods. Suspected symptoms of endometriosis or persistent iron deficiency also belong with a doctor.

References

[1] National Institute of Child Health and Human Development. Menstruation and Menstrual Problems. NIH. nichd.nih.gov/health/topics/menstruation

[2] American College of Obstetricians and Gynecologists. Menstruation in Girls and Adolescents: Using the Menstrual Cycle as a Vital Sign. Committee Opinion 651. acog.org

[3] Ferries-Rowe E, Corey E, Archer JS. Primary dysmenorrhea: diagnosis and therapy. Obstetrics and Gynecology 2020;136(5):1047-1058. doi.org/10.1097/AOG.0000000000004096

[4] Li R, Li B, Kreher DA, et al. Association between dysmenorrhea and chronic pain: a systematic review and meta-analysis of population-based studies. American Journal of Obstetrics and Gynecology 2020;223(3):350-371. doi.org/10.1016/j.ajog.2020.03.002

[5] Guimarães I, Póvoa AM. Primary dysmenorrhea: assessment and treatment. Revista Brasileira de Ginecologia e Obstetrícia 2020;42(8):501-507. doi.org/10.1055/s-0040-1712131

[6] Nuha K, Rusmil K, Ganiem AR, et al. Single-blind randomized controlled trial: comparative efficacy of dark chocolate, coconut water, and ibuprofen in managing primary dysmenorrhea. International Journal of Environmental Research and Public Health 2023;20(16):6619. doi.org/10.3390/ijerph20166619

[7] World Health Organization. Endometriosis fact sheet. WHO. who.int/news-room/fact-sheets/detail/endometriosis

[8] Giudice LC, Horne AW, Missmer SA. Time for global health policy and research leaders to prioritize endometriosis. Nature Communications 2023;14(1):8028. doi.org/10.1038/s41467-023-43913-9

[9] Yu EH, Joo JK. Commentary on the new 2022 European Society of Human Reproduction and Embryology (ESHRE) endometriosis guidelines. Clinical and Experimental Reproductive Medicine 2022;49(4):219-224. doi.org/10.5653/cerm.2022.05603

[10] Brandes I, Kleine-Budde K, Heinze N, et al. Cross-sectional study for derivation of a cut-off value for identification of an early versus delayed diagnosis of endometriosis. BMC Women's Health 2022;22(1):521. doi.org/10.1186/s12905-022-02044-x

[11] National Institutes of Health, Office of Dietary Supplements. Iron Fact Sheet for Health Professionals. NIH ODS. ods.od.nih.gov/factsheets/Iron-HealthProfessional

[12] Munro MG, Mast AE, Powers JM, et al. The relationship between heavy menstrual bleeding, iron deficiency, and iron deficiency anemia. American Journal of Obstetrics and Gynecology 2023;229(1):1-9. doi.org/10.1016/j.ajog.2023.01.017

[13] Mei Z, Addo OY, Jefferds ME, et al. Physiologically based serum ferritin thresholds for iron deficiency in children and non-pregnant women: a US National Health and Nutrition Examination Surveys (NHANES) serial cross-sectional study. The Lancet Haematology 2021;8(8):e572-e582. doi.org/10.1016/S2352-3026(21)00168-X

[14] Garcia-Casal MN, Pasricha SR, Martinez RX, et al. Serum or plasma ferritin concentration as an index of iron deficiency and overload. Cochrane Database of Systematic Reviews 2021;5(5):CD011817. doi.org/10.1002/14651858.CD011817.pub2

[15] Mariné-Casadó R, Tobajas Y, Antolín A, et al. Comparative study of the effects of different iron sources on bioavailability and gastrointestinal tolerability in iron-deficient rats. Scientific Reports 2025;15(1):21033. doi.org/10.1038/s41598-025-07202-3

[16] Cappellini MD, Santini V, Braxs C, Shander A. Iron metabolism and iron deficiency anemia in women. Fertility and Sterility 2022;118(4):607-614. doi.org/10.1016/j.fertnstert.2022.08.014