Iron deficiency is the most common nutritional deficiency in the world. According to the Global Burden of Disease Study 2021, published in The Lancet Haematology, approximately 1.92 billion people worldwide suffer from anaemia — and dietary iron deficiency accounts for 66.2% of those cases.
If you've ever taken an iron supplement and experienced bloating, constipation, or nausea, you're not alone. Those side effects are one of the main reasons people stop taking iron, even when they need it. But the issue usually isn't the amount of iron — it's the form.
Two Forms of Dietary Iron
Iron exists in two distinct chemical forms, and understanding the difference can save you months of trial and error with supplements that don't work.
Haem iron is the form found naturally bound within a haemoglobin molecule — the protein in red blood cells that carries oxygen throughout your body. You consume haem iron when you eat red meat, poultry, or fish.
Non-haem iron is found in plants, fortified foods, and most over-the-counter iron supplements (ferrous sulphate, ferrous gluconate). It's not bound within haemoglobin and must undergo a more complex conversion before your body can use it.
The Absorption Gap: What the Research Shows
The difference in bioavailability between these two forms is significant and well-established in nutrition science.
In a landmark study published in the Journal of the American Dietetic Association, Monsen (1988) established that 15% to 35% of haem iron is absorbed from a meal, depending on the individual's existing iron stores (PubMed: 3290310).
Non-haem iron absorption is dramatically lower. The NIH Office of Dietary Supplements reports that iron bioavailability ranges from 14-18% on mixed diets containing meat and Vitamin C, dropping to just 5-12% on vegetarian diets — and as low as 2-5% from meals without absorption enhancers.
Hallberg and Hulthén (2000) quantified this further in the American Journal of Clinical Nutrition: haem iron contributes only about one-third of dietary iron intake, but can account for more than 40% of total absorbed iron due to its superior bioavailability (AJCN, 71(5):1147-1160).
Why Haem Iron Bypasses Common Absorption Blockers
One of haem iron's most important advantages is that it uses a completely separate absorption pathway in the gut.
As described by West and Oates (2008) in the World Journal of Gastroenterology, haem iron is absorbed intact — still bound within its protoporphyrin ring — through specific membrane receptors on intestinal cells. Once inside the cell, the enzyme haem oxygenase releases the iron for use. This separate pathway means that the dietary compounds which block non-haem iron simply don't affect haem iron absorption (WJG, 14(26):4101-4110).
A comprehensive 2020 review by Milman in the Journal of Nutrition and Metabolism confirmed that haem iron remains "relatively independent of the effects of various promoters and inhibitors of iron absorption in the food matrix." The review found that polyphenols (found in tea and coffee) reduce non-haem iron absorption by 60-90% at typical serving amounts, and phytates (found in grains and legumes) inhibit absorption in a dose-dependent manner. Haem iron bypasses both (DOI: 10.1155/2020/7373498).
The one exception: calcium is the only dietary inhibitor shown to reduce absorption of both haem and non-haem iron. If you take an iron supplement, spacing it away from dairy products or calcium supplements is good practice regardless of the form.
Fewer Side Effects: The Clinical Evidence
Most iron supplement side effects — constipation, nausea, stomach cramps — come from unabsorbed iron irritating the digestive tract. Because non-haem iron has lower absorption, a larger portion of each dose passes through undigested.
A 2024 systematic review and meta-analysis by Gallo Ruelas et al., published in the European Journal of Nutrition, analysed 13 randomised controlled trials with 910 participants. The findings: participants receiving haem iron had a 38% relative risk reduction in total side effects compared to those taking non-haem iron (RR 0.62; 95% CI 0.40–0.96). In children with anaemia or depleted iron stores, haem iron also showed superior haemoglobin increases (DOI: 10.1007/s00394-024-03564-y).
If you've previously given up on iron supplements because of digestive discomfort, a haem-based formula may be worth considering.
Who May Benefit From Iron Supplementation?
You may benefit from additional iron support if you:
- Feel persistently tired, even after adequate sleep
- Experience brain fog or difficulty concentrating
- Are a woman with heavy menstrual periods
- Follow a vegetarian or vegan diet (plant-based iron is exclusively non-haem)
- Exercise regularly — athletes lose iron through sweat and increased red blood cell turnover
- Are recovering from illness or surgery
- Have been told by your doctor that your ferritin or haemoglobin levels are low
If you suspect iron deficiency, a blood test measuring ferritin (stored iron) and haemoglobin levels is the most reliable way to confirm. Talk to your doctor before starting supplementation, especially if you are pregnant, breastfeeding, or taking prescription medication.
Deer Blood: A Traditional Source of Natural Haem Iron
In New Zealand, deer blood has been valued as a natural source of haem iron for decades. It provides iron in its natural biological matrix — alongside bioavailable protein and amino acids — rather than as an isolated mineral salt.
A 2020 study by Liu et al. published in Animal Production Science (CSIRO) investigated deer blood supplementation in an iron-deficiency anaemia model. The results showed that deer blood significantly increased iron concentrations in liver, spleen, and kidney tissue compared to control groups (DOI: 10.1071/AN19510). While this was an animal study and further human clinical trials would strengthen the evidence, the findings are consistent with the broader haem iron research base.
Deep Blue Health Haem Iron capsules combine 200mg of NZ Deer Blood Powder with 20mg of Ferrous Fumarate, creating a dual-source formula providing both haem and non-haem iron. The deer blood is sourced from premium farms on New Zealand's South Island.
Try It For Yourself
Deep Blue Health Haem Iron
200mg NZ Deer Blood Powder + 20mg Ferrous Fumarate per capsule. Dual-source formula, 90 capsules, NZ laboratory tested.
Shop Haem Iron →Practical Tips for Better Iron Absorption
Whichever iron supplement you take, these evidence-based habits support absorption:
- Take with Vitamin C — ascorbic acid is the most potent enhancer of non-haem iron absorption and supports overall iron utilisation
- Avoid tea and coffee within one hour — polyphenols and tannins can reduce non-haem iron absorption by 60-90% (Milman, 2020)
- Space away from calcium — the one inhibitor that affects both forms of iron
- Be consistent — iron stores rebuild gradually over 4-8 weeks of daily supplementation
- Get tested — if fatigue persists after a month, ask your doctor to check ferritin levels
Frequently Asked Questions
What is the difference between haem and non-haem iron?
Haem iron is the form of iron found in red meat, fish, poultry, and blood — it's already bound inside a haemoglobin or myoglobin molecule. Non-haem iron is the form found in plants, fortified foods, and most supplements (ferrous sulfate, ferrous gluconate, ferrous fumarate). The two are absorbed by different pathways, which is why haem iron has 2–4× higher bioavailability.
How much haem iron should I take per day?
There is no official recommended daily allowance specifically for haem iron — the RDA for total iron is 8 mg/day for men and post-menopausal women, and 18 mg/day for menstruating women (NIH ODS). Supplement doses typically provide 15–30 mg of elemental iron daily. Always follow the label and consult your doctor if unsure.
Can I take haem iron with food?
Yes — and it's usually recommended. Taking iron with a meal reduces the risk of stomach discomfort, and vitamin C from food or juice further supports absorption. Avoid taking iron within one hour of tea, coffee, or calcium-rich foods, which can reduce absorption (particularly for the non-haem portion).
How long does it take to correct iron deficiency?
Haemoglobin levels typically begin rising within 2–4 weeks of consistent supplementation. Full restoration of iron stores (ferritin) usually takes 2–6 months, depending on the severity of the deficiency. Most people notice improvements in energy and fatigue within the first month.
Is deer blood safe to take as a supplement?
Yes. Deer blood powder used in supplements is processed under food-grade manufacturing standards and has been used as a natural iron source in traditional Chinese medicine and New Zealand wellness products for decades. Deep Blue Health Haem Iron is NZ laboratory tested and produced under HACCP and GMP principles. Always check with your doctor if you are pregnant, breastfeeding, or taking prescription medication.
The Bottom Line
Not all iron supplements are equal. Over three decades of research consistently shows that haem iron absorbs at 15-35% compared to 2-12% for non-haem iron, bypasses most dietary absorption inhibitors, and causes significantly fewer digestive side effects. If you're supplementing iron, the form matters as much as the dose.
References
- GBD 2021 Anaemia Collaborators. (2023). Prevalence, years lived with disability, and trends in anaemia burden by severity and cause, 1990–2021. The Lancet Haematology. DOI: 10.1016/S2352-3026(23)00160-6
- Monsen ER. (1988). Iron nutrition and absorption: dietary factors which impact iron bioavailability. Journal of the American Dietetic Association, 88(7):786-790. PubMed: 3290310
- Hallberg L, Hulthén L. (2000). Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron. American Journal of Clinical Nutrition, 71(5):1147-1160. AJCN
- NIH Office of Dietary Supplements. (2025). Iron — Health Professional Fact Sheet. NIH ODS
- West AR, Oates PS. (2008). Mechanisms of heme iron absorption. World Journal of Gastroenterology, 14(26):4101-4110. DOI: 10.3748/wjg.14.4101
- Milman NT. (2020). A review of nutrients and compounds which promote or inhibit intestinal iron absorption. Journal of Nutrition and Metabolism. DOI: 10.1155/2020/7373498
- Gallo Ruelas M, et al. (2024). Effectiveness and side effects of heme iron versus non-heme iron: a systematic review and meta-analysis. European Journal of Nutrition. DOI: 10.1007/s00394-024-03564-y
- Liu R, et al. (2020). Effects of deer blood on iron-deficiency anaemia. Animal Production Science (CSIRO). DOI: 10.1071/AN19510
Deep Blue Health Haem Iron is available in 60 and 90 capsule bottles. NZ laboratory quality tested. Made under internationally recognised HACCP Principles and Good Manufacturing Practices. No artificial flavours, colours, or preservatives.
This article is for educational purposes only and does not constitute medical advice. If you suspect iron deficiency, consult your healthcare professional for diagnosis and personalised treatment.
