By Aleisha Smith, Registered Nutritionist (NSNZ)
Around one in five women of reproductive age in the UK is iron deficient. Most have no idea.
Before pregnancy, five nutrients do most of the heavy lifting for fertility: iron, folate, iodine, zinc and vitamin D. Below: how much you need, where your blood levels should sit, when to supplement, and where to find each in food.
General information only, not personal medical advice. Chat to your GP before starting supplements.
How much you need each day
Needs rise in pregnancy for most of these, but iron drops while breastfeeding because periods usually pause, and vitamin D stays steady.
| Nutrient | Trying to conceive | Pregnant | Breastfeeding |
|---|---|---|---|
| Iron | 18 mg | 27 mg | 9 mg |
| Folate | 400 µg DFE | 600 µg DFE | 500 µg DFE |
| Iodine | 150 µg | 220 µg | 270 µg |
| Zinc | 8 mg | 11 mg | 12 mg |
| Vitamin D | 5 µg (200 IU) | 5 µg (200 IU) | 5 µg (200 IU) |
Source: NZ/Australian Nutrient Reference Values for women 19 to 50 (vitamin D is an Adequate Intake).
Where your blood markers should sit
Ask your GP for ferritin, haemoglobin and vitamin D tests; the others are usually checked when there is a reason, such as long-term pill use or a thyroid concern.
| Nutrient (test) | Trying to conceive | Pregnant | Breastfeeding |
|---|---|---|---|
| Iron (ferritin) | 30 µg/L or above | 30 µg/L or above | 30 µg/L or above |
| Iron (haemoglobin) | 120 g/L or above | 110 g/L or above | 120 g/L or above |
| Folate (red cell folate) | 906 nmol/L or above | 906 nmol/L or above | Above 340 nmol/L |
| Iodine (urinary iodine, median) | 100 to 199 µg/L | 150 to 249 µg/L | 100 µg/L or above |
| Zinc (serum) | About 10 to 18 µmol/L | Runs lower; your GP interprets | About 10 to 18 µmol/L |
| Vitamin D (25-hydroxyvitamin D) | 50 nmol/L or above | 50 nmol/L or above | 50 nmol/L or above |
Ferritin below 30 µg/L means depleted iron stores, and below 15 µg/L is clearly deficient. Urinary iodine is a population marker, so a single spot sample is only a rough guide for you. Lab ranges vary, so use the range printed on your own results.
Iron
Why it matters for fertility. Healthy iron supports regular ovulation and egg development, and demand surges once you are pregnant. Monthly blood loss is the leading cause of deficiency at this life stage.
Supplement? Only if a blood test shows low iron. Your GP will choose the dose, and more is not better (upper limit 45 mg per day).
Food sources. Haem iron, which is best absorbed: red meat, liver, poultry. Non-haem iron: lentils, tofu, nuts, seeds, fortified cereals. Eat these with vitamin C (capsicum, citrus) to lift absorption.
Folate
Why it matters for fertility. Folate supports cell division and egg quality, and the neural tube closes in the first weeks of pregnancy, often before you know you are pregnant. Stores need to be full beforehand.
Supplement? Yes, for anyone planning a pregnancy. NZ Ministry of Health advice is 800 µg folic acid daily from at least four weeks before conception until 12 weeks of pregnancy, and starting about three months ahead builds stores well (Australian guidance is around 500 µg). A higher prescribed dose may be needed with a history of neural tube defects, diabetes or certain medications.
Food sources. Leafy greens, legumes, asparagus, avocado, citrus, eggs, and fortified bread and cereals.
Iodine
Why it matters for fertility. Iodine builds the thyroid hormones that regulate ovulation and your cycle, and your baby's brain depends on them from early pregnancy. Too little and too much both disrupt the thyroid, so optimise it before conception rather than reactively.
Supplement? NZ Ministry of Health recommends 150 µg iodine daily throughout pregnancy and breastfeeding, and many clinicians suggest starting when trying to conceive. Check with your GP first if you have a thyroid condition (upper limit 1100 µg per day).
Food sources. Iodised salt, fortified bread, dairy, seafood, eggs and seaweed (keep portions modest, as kelp varies hugely).
Zinc
Why it matters for fertility. Zinc supports egg maturation, ovulation hormones and immunity, and it matters for male partners too, through sperm production and testosterone. Plant-based eaters (phytic acid binds zinc) and long-term pill users are at higher risk.
Supplement? Worth considering if you are at higher risk or your levels are low. Stay under 40 mg per day, as too much zinc can interfere with copper.
Food sources. Red meat, shellfish (especially oysters), dairy, legumes, nuts and seeds. Soaking, sprouting or fermenting legumes and grains improves absorption.
Vitamin D
Why it matters for fertility. Vitamin D is linked to hormone balance and implantation, and it helps you absorb calcium. Insufficiency is common, rising to roughly a third of adults over winter in the UK and Australia.
Supplement? Late winter to early spring is when it is most worth considering. About 1000 IU (25 µg) daily, taken consistently, is often effective, ideally after a blood test (upper limit 80 µg per day).
Food sources. Oily fish (salmon, mackerel, sardines), egg yolks, fortified milk and cereals, and UV-exposed mushrooms. Eat them with some fat, as vitamin D is fat soluble. Food gives only a little, and sun exposure helps but needs balancing against New Zealand's high UV.
The takeaway
Ask your GP for ferritin, haemoglobin and vitamin D tests before you start trying. Begin folate early, plan for iodine, and check your zinc risk factors. Start with food, and test before you guess.