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Body notes · Note No. 8

What our food lost, and what your cycle needs

Test, don't guess. A blood test costs less than a month of pills you might not need.

September 22, 2026

Something I've been reading into, and it turned into more than a note: the vegetables and fruit we buy today carry less of some minerals and vitamins than the same crops 50 to 80 years ago — the studies put it between roughly 6 and 38 percent depending on the nutrient. That matters more for women than for most people, because iron, magnesium, B6 and vitamin D all move with the cycle. So here is the long version: what the studies actually show, where women stand today, what a period costs in iron, and what to do about it. Every number has a source at the bottom.

A note on how this came about: a friend pointed me to the nutrition score printed on many German products, A to E. We stood in the shop and most of what we picked up was a D or an E. The first A we found was a mix of nuts and seeds that looked like bird food. Since then I read that little label, and I read the studies below. Otherwise we just get full, fat and tired, when we could eat less and feel energised because the body got what it needs.

lentils, oats, pumpkin seeds, kale, spinach, pomegranate and a glass of water with lemon

what changed in our food

the most cited study compared US nutrition tables for 43 garden crops, 1950 versus 19991. six of thirteen nutrients showed a reliable drop in the median: protein −6 %, phosphorus −9 %, iron −15 %, vitamin C −15 %, calcium −16 %, riboflavin (B2) −38 %. the other seven did not change reliably. a UK comparison of 1940 versus 2019 found iron −50 %, copper −49 % and magnesium −10 % across 20 vegetables and 20 fruits2,3.

bar chart: median change in 43 garden crops, USA 1950 to 1999: protein −6 %, phosphorus −9 %, iron −15 %, vitamin C −15 %, calcium −16 %, riboflavin −38 %

only 6 of 13 nutrients showed a reliable change; 7 did not. source: Davis, Epp & Riordan, J Am Coll Nutr 2004.

the honest caveat. a 2017 review4 warns that comparing tables decades apart is shaky: varieties, origin, ripeness and lab methods all changed. the "30 % less" headline you may have seen is a simplification. what holds up: some nutrients in some crops are lower, most plausibly because of high-yield varieties (the "dilution effect"), and this is best documented in wheat. the variety you buy and how fresh it is matter more than the decade.

where women actually stand

the food tables are the small story. the big one is what is measured in women's blood and diets today5–10:

bar chart: anaemia in women 15–49: world 30.7 %, EU 17 %; iron deficiency in menstruating women 22 %; vitamin D below 50 nmol/L in Germany 61.6 %; folate intake below reference in German women 86 %

sources: WHO / World Bank 2023 · Blood 2025 meta-analysis of 71 studies (270,907 women) · RKI DEGS1 (6,995 adults) · Nationale Verzehrsstudie II.

what this has to do with your cycle

every period costs iron. about 0.4–0.5 mg per millilitre of blood; the median bleed is 20–30 ml, so roughly 10–15 mg per cycle14–16. with heavy periods (over 80 ml, fewer than 1 in 10 women) it is 32–40 mg. that is why heavy bleeding is a named risk group for iron deficiency, and why a ferritin test is the first thing gynaecologists recommend when bleeding is heavy14,15.

animation: a 28-day cycle ring, the first five days marked, counting up to about 12.5 mg of iron lost with the bleed; daily reference 16 mg

reference intake for women 19–50: 16 mg iron per day from food (DGE 2024). the body absorbs only a fraction, which is why the daily number is higher than the monthly loss.

and the supplements everyone talks about for PMS and cramps? here is what the trials actually show, sorted by how solid the evidence is:

nutrientwhat was foundevidence
ironmeasured deficiency is common and the fix is well established: eat iron-rich food, test ferritin if periods are heavy or you are often tired7,14,15strong
calcium1,200 mg/day for 3 cycles cut PMS symptom scores by 48 % vs 30 % on placebo in 466 women. one large trial, 199822moderate
vitamin B69 trials, 940 women: about twice the odds of PMS improvement. but the trials were of mixed quality, and the EU safety limit is now 12 mg/day because of nerve damage at high doses20,21moderate, dose caution
omega-38 small studies: clearly less period pain at 300–1,800 mg/day over 2–3 months. promising, not proven26,27moderate
magnesium"promising" for cramps in 2001, "no high-quality evidence" in the 2016 update; for PMS "insufficient evidence" in 202417–19weak / mixed
vitamin Dless period pain in two meta-analyses, but mostly high-dose trials that disagree with each other; PMS: inconclusive23–25weak / mixed
"detox"no trial base at all. megadoses have documented harm: B6 above 12 mg, iron above 40 mg, supplemental magnesium above 250 mg21,28,29none

what to actually do

food first. these are the german reference values for women 19–50 and where the nutrients sit30–35:

nutrientper daybest from
iron16 mg (11 mg if you don't menstruate)lentils, beans, oats, pumpkin seeds, red meat. add vitamin C (peppers, citrus), keep coffee and tea an hour away
magnesium300 mgwhole grains, nuts, seeds, legumes, dark greens
vitamin D20 µg when there is no sunoily fish, eggs; sun on skin april–september
folate300 µg (+400 µg folic acid if pregnancy is possible)greens, legumes, whole grain
iodine150 µgiodised salt, sea fish, dairy
B124 µganimal foods; vegans: supplement, no way around it

test, don't guess. ferritin (plus CRP) if your periods are heavy, tiredness won't go, or you eat mostly plants. 25(OH)-vitamin D in winter. B12 if you are vegan. then supplement only the measured gap, within the safety limits, with your doctor. a blood test costs less than a month of pills you might not need.

Sources
  1. Davis DR, Epp MD, Riordan HD. Changes in USDA food composition data for 43 garden crops, 1950 to 1999. J Am Coll Nutr 2004;23:669–82. pubmed
  2. Mayer AM. Historical changes in the mineral content of fruits and vegetables. Br Food J 1997;99:207–11.
  3. Mayer AM, Trenchard L, Rayns F. Historical changes in the mineral content of fruit and vegetables in the UK from 1940 to 2019. Int J Food Sci Nutr 2022;73:315–26. link
  4. Marles RJ. Mineral nutrient composition of vegetables, fruits and grains: the context of reports of apparent historical declines. J Food Compos Anal 2017;56:93–103. link
  5. Stevens GA et al. National, regional, and global estimates of anaemia by severity in women and children, 2000–19. Lancet Glob Health 2022. link
  6. WHO estimates via World Bank, indicator SH.ANM.NPRG.ZS, 2023. link
  7. Global prevalence of iron deficiency in menstruating women, meta-analysis of 71 studies. Blood 2025. link
  8. Swiss cross-sectional study on iron status in young women. link
  9. Nationale Verzehrsstudie II, Ergebnisbericht Teil 2, Max Rubner-Institut 2008, pp. 133–170. pdf
  10. Rabenberg M et al. Vitamin D status among adults in Germany (DEGS1). BMC Public Health 2015. link
  11. Pawlak R et al. Prevalence of cobalamin deficiency among vegetarians. Eur J Clin Nutr 2014. link
  12. Micronutrient status of omnivores, vegetarians and vegans in Germany. Ann Med 2023. link
  13. BMLEH / RKI, Jodversorgung in Deutschland (DEGS). link
  14. ACOG Committee Opinion 785, Screening and management of bleeding disorders in adolescents with heavy menstrual bleeding, 2019. link
  15. NIH Office of Dietary Supplements, Iron fact sheet for health professionals. link
  16. Institute of Medicine, Dietary Reference Intakes: Iron (menstrual blood-loss medians). link
  17. Proctor ML, Murphy PA. Herbal and dietary therapies for primary and secondary dysmenorrhoea. Cochrane 2001. link
  18. Pattanittum P et al. Dietary supplements for dysmenorrhoea. Cochrane 2016. link
  19. Magnesium and premenstrual syndrome, systematic review of RCTs. Nutrition Reviews 2025;83:280. link
  20. Wyatt KM et al. Efficacy of vitamin B6 in the treatment of premenstrual syndrome: systematic review. BMJ 1999. link
  21. EFSA, Scientific opinion on the tolerable upper intake level for vitamin B6, 2023. link
  22. Thys-Jacobs S et al. Calcium carbonate and the premenstrual syndrome. Am J Obstet Gynecol 1998. link
  23. Vitamin D supplementation for primary dysmenorrhoea, meta-analysis 2023. link
  24. Vitamin D and dysmenorrhoea, meta-analysis with trial sequential analysis 2024. link
  25. Arab A et al. Vitamin D and premenstrual syndrome. J Am Coll Nutr 2019. link
  26. Snipe RMJ et al. Omega-3 and dysmenorrhoea, systematic review. Nutr Diet 2024. link
  27. Omega-3 fatty acids for primary dysmenorrhoea, meta-analysis. Eur J Clin Pharmacol 2022. link
  28. EFSA, Safe level of intake for iron, 2024. link
  29. BfR, Maximum daily level for magnesium in food supplements. link
  30. DGE, Referenzwerte Eisen (2024). link
  31. DGE, Referenzwerte Magnesium. link
  32. DGE, Referenzwerte Vitamin D. link
  33. DGE, Referenzwerte Folat. link
  34. DGE, Referenzwerte Jod (2025). link
  35. DGE, Referenzwerte Vitamin B12. link

this is general information, not medical advice. if something feels off, talk to your doctor.

— Christian

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