If you feel inexplicably exhausted during or after your period, iron might be the reason. Not "might" in the vague wellness sense — might in the statistically-probable sense. The World Health Organisation estimates that 30% of menstruating women globally are iron deficient, and a 2022 Lancet study found that figure rises to 40% in women with heavy periods.
The average menstrual blood loss is 30–40ml per cycle. Each millilitre of blood contains approximately 0.5mg of iron. That is 15–20mg of iron lost per period — nearly the entire recommended daily intake for premenopausal women (18mg/day in the UK). If your periods are heavier than average, you are likely losing more iron than you are replacing.
How to know if you are low
Iron deficiency does not always announce itself dramatically. It creeps in. The symptoms overlap with general fatigue, stress, and poor sleep, which is why so many women dismiss them.
Common signs of iron deficiency
- Fatigue that is not relieved by sleep — the hallmark symptom
- Breathlessness during exercise you normally handle easily
- Difficulty concentrating or brain fog, especially mid-afternoon
- Pale inner eyelids and nail beds
- Restless legs, particularly at night
- Unusually heavy or prolonged periods (iron deficiency can worsen bleeding, creating a vicious cycle)
- Craving ice, dirt, or starch (pica) — a surprisingly specific diagnostic clue
A serum ferritin test is the gold standard. Ferritin measures your iron stores, not just circulating iron. The NHS considers ferritin below 15 µg/L as deficient, but many researchers argue that symptoms begin when ferritin drops below 30 µg/L. Ask your GP for the actual number, not just whether it is "normal."
Iron-rich foods that actually work
There are two types of dietary iron: haem iron (from animal sources) and non-haem iron (from plants). Haem iron is absorbed at roughly 15–35% efficiency. Non-haem iron is absorbed at 2–20%. This does not mean plant-based diets cannot meet iron needs — it means strategy matters.
Top haem iron sources (per 100g)
- Chicken liver — 11mg (also extremely rich in folate and B12)
- Beef — 3.5mg
- Sardines — 2.9mg
- Dark turkey meat — 2.3mg
- Mussels — 6.7mg (one of the highest food sources available)
Top non-haem iron sources (per 100g)
- Pumpkin seeds — 8.8mg
- Firm tofu — 5.4mg
- Cooked lentils — 3.3mg
- Cooked spinach — 3.6mg (but high in oxalates — see below)
- Dark chocolate (70%+) — 11.9mg per 100g (roughly 3.4mg per 28g serving)
The absorption game
Getting iron into your food is only half the equation. Getting it into your bloodstream is the other half. Absorption enhancers and inhibitors make an enormous practical difference.
Absorption Boost
Pair iron-rich foods with vitamin C at the same meal. A 1989 study in the American Journal of Clinical Nutrition showed that adding 100mg of vitamin C (one medium capsicum or a glass of orange juice) increased non-haem iron absorption by up to 6-fold. This single change can transform a plant-based diet's iron delivery.
Absorption inhibitors to time carefully
- Tea and coffee — tannins reduce absorption by 60–70%. Wait 30 minutes after an iron-rich meal.
- Calcium — dairy and calcium supplements compete directly with iron for absorption. Separate them by at least 2 hours.
- Phytates — found in whole grains and legumes. Soaking, sprouting, or fermenting reduces phytate content significantly.
- Oxalates — spinach is iron-rich but oxalate-heavy. Cooking reduces oxalates by 30–90%. Kale is a better bet for absorbable iron.
A week of iron-smart eating during your period
You do not need to overhaul your diet. Small, strategic additions during your menstrual phase can meaningfully shift your iron balance.
Practical meal ideas
- Breakfast: Porridge with pumpkin seeds and strawberries (iron + vitamin C pairing)
- Lunch: Lentil soup with a squeeze of lemon and crusty bread
- Snack: Dark chocolate (70%+) and an orange
- Dinner: Stir-fried tofu with capsicum, broccoli, and brown rice
- Alternative dinner: Mussels in tomato-based sauce with sourdough
Phase Tip
Cast-iron cookware leaches small amounts of iron into food during cooking — particularly acidic foods like tomato-based sauces. A 2003 study in the Journal of the American Dietetic Association found it can increase a dish's iron content by 1–5mg. It is not a supplement, but it helps.
When to consider supplementation
Dietary changes alone may not be enough if your ferritin is already low (below 30 µg/L) or your periods are consistently heavy. In those cases, supplementation under medical guidance is reasonable.
Standard iron supplements (ferrous sulphate, 200mg tablets containing 65mg elemental iron) are effective but notoriously hard on the stomach. A 2015 Lancet Haematology trial found that taking iron every other day — rather than daily — actually improved absorption by 40% while halving gastrointestinal side effects. The body upregulates hepcidin (an iron-regulating hormone) after each dose, so alternate-day dosing works with your physiology rather than against it.
Iron deficiency is the most prevalent nutritional deficiency in the world, yet it remains under-recognised and undertreated in menstruating women.
— World Health Organisation, Global Anaemia Report 2023
Iron deficiency is common, consequential, and largely correctable. You do not have to accept post-period exhaustion as inevitable. Track your energy across your cycle, ask for a ferritin test at your next appointment, and start pairing your iron with vitamin C. The difference can be remarkable.