Overview
While iron and vitamin D typically do not interact to cause negative effects, it is probably best to consume them separately. This is because iron is best absorbed when consumed on an empty stomach while vitamin D is best absorbed after a fat-containing meal.
As both iron and vitamin D are important nutrients involved in many metabolic and growth processes, knowing how and when to consume these nutrients will help the body absorb them optimally.
Role of iron
Iron has several important functions in the body, including red blood cell synthesis, oxygen transportation, and DNA synthesis and repair. Iron levels in the body need to be tightly regulated because low levels can cause iron-deficiency anaemia while high levels can lead to toxicity.1
There are 2 main forms of iron that we take in through food sources: heme iron and non-heme iron. Food sources that provide heme iron include:
- meats
- seafood
- poultry
The main food sources that provide non-heme iron are:
- fruits and vegetables
- iron-fortified foods
- nuts
- beans
Heme iron is readily absorbed by the body into the blood circulation (15%-35% absorption), while non-heme iron is less readily absorbed than heme iron (2%-20% absorption).1 The absorption of heme iron is not normally affected by the presence of other nutrients, with some exceptions such as calcium, which inhibits its absorption. On the other hand, non-heme iron’s absorption is strongly influenced by the presence of other nutrients.1
Iron is absorbed from food in the intestines, and is then transported to different regions in the body, for example, to the bone marrow for making red blood cells. The body regulates iron absorption such as when there is sufficient iron in the body, less iron will be taken up. Iron is also recycled from red blood cells that are broken down at the end of their lifespan.
Up to 70% of the iron in our body is located in haemoglobin, a component in red blood cells that makes blood appear red. Haemoglobin is made up of 4 protein chains, each chain consists of 1 iron-containing heme group which can bind to oxygen and facilitate oxygen transportation. Iron binds to oxygen and is oxidised from soluble ferrous ion (Fe2+) to insoluble ferric ion (Fe3+). Oxygen can then be transported around the body and dissociates from the haemoglobin to provide body tissues with oxygen.
Iron is also essential in several enzymes involved in DNA synthesis and repair. For example, iron is present in replicative DNA polymerases which replicate DNA, and in DNA helicases which help unwind the DNA double helix for replication and reparation.2
Symptoms of low iron levels
Normal serum iron levels for adults should be in the range of 60 to 170 μg/dL. An iron level <56 μg/dL is associated with an iron deficiency which is the most common cause of anaemia.
You may experience the following symptoms if you have iron deficiency:
- Fatigue
- Shortness of breath
- Elevated heart rate
- Pale skin
- Cold hands and feet
People with low iron levels can increase their iron levels by taking iron-rich foods, such as:
- meat
- poultry
- seafood
- beans
- cereals,
- dates
- vegetables such as spinach and broccoli
Taking foods high in vitamin C or vitamin C supplements can also help in the absorption of iron. If your doctor prescribed iron pills to you, such as ferrous sulphate, consume them according to their advice.
Role of vitamin D
Vitamin D exists in 2 main forms: vitamin D2 and vitamin D3. Vitamin D2 is normally acquired from foods such as plants, fortified foods (which contain additional nutrients that don’t normally occur in the food) and oral supplements; vitamin D3 is normally produced in the skin after the body absorbs ultraviolet rays from sunlight and also exists in some fish products and oral supplements.3
When the skin absorbs ultraviolet B (UVB) rays, provitamin D3 is converted into vitamin D. From the skin, vitamin D is transported to the liver then the kidneys to be processed into its active form, calcitriol. Keratinocytes in the skin can also convert vitamin D into calcitriol.
Vitamin D is essential in building bones and maintaining bone health. Vitamin D promotes the absorption of calcium and phosphorus, which are both required for bone mineralisation - the process of incorporating these minerals when building bones. Vitamin D is also involved in maintaining muscle size, strength and contractility.4
The immune system also requires vitamin D to fight pathogens as vitamin D enhances the action of some of the innate immune cells. For example, calcitriol can be locally produced in the monocytes from vitamin D’s intermediate product and promotes the production of a protein to kill tuberculosis bacteria in the monocytes.5
Vitamin D also helps in the production of red blood cells. Vitamin D can bind to vitamin D receptors on the precursor cells of red blood cells and induce their maturation.6
Symptoms of low vitamin D levels
Vitamin D level is usually indicated by serum 25-hydroxyvitamin D level. Vitamin D level should be >30 ng/ml to be considered sufficient. A person with a vitamin D level <20 ng/ml is considered deficient in vitamin D.
If you have low vitamin D levels, you might show some of the following symptoms:
- Muscle weakness or muscle cramps
- Fatigue
- Bone pain
- Mood changes
Can you take iron and vitamin D together?
The short answer is yes, you can take iron and vitamin D together. Vitamin D does not affect iron absorption and oxidation like some other vitamins do, such as vitamins A and C have been suggested to enhance iron absorption.7
But, should you take iron and vitamin D supplements together?
It is probably best to consume iron and vitamin D separately and consult your healthcare provider for advice. This is because while there is no known interaction between the two nutrients that cause negative effects, a study done in 2018 showed that vitamin D may inhibit iron absorption in healthy individuals who have a slightly lower level of vitamin D.8
Besides that, iron is best absorbed when taken on an empty stomach, while vitamin D is best absorbed after a meal because it is a fat-soluble nutrient. Therefore, taking iron and vitamin D together may mean that one of the nutrients is not absorbed optimally.
What should you not take with iron?
Calcium supplements
Calcium in calcium supplements was suggested to reduce the absorption of non-heme iron and heme iron by blocking the transport of iron from the intestinal lumen into the mucosal epithelial cells.9 It is best to consume iron and calcium supplements at least 2 hours apart.
Cheese
Cheese contains calcium which inhibits the absorption of heme and non-heme iron, so it is probably best to take iron at least 2 hours after iron supplements.
Eggs
Phosvitin is the main protein found in the egg yolk. Phosvitin binds to iron and causes the formation of insoluble iron complex, which reduces the absorption of iron in the intestines.10 It is probably best to take iron supplements at least 2 hours before or after a meal containing eggs.
Antacids
Antacids are medications that neutralise stomach acid (making it less acidic) to relieve heartburn and indigestion. Iron absorption is better in acidic environment, so antacids inhibit the absorption of iron. Antacids also contain calcium which inhibits iron absorption. After taking antacids, it is advised to wait at least 2 hours before taking iron supplements.11
Tea
Non-herbal teas contain tannins which can reduce the absorption of non-heme iron.12 It is recommended to consume non-herbal tea and iron-containing foods or iron supplements at least 1 hour apart to avoid affecting iron absorption.13
What should you not take with vitamin D?
Cholesterol and blood pressure lowering drugs
Cholestyramine is a cholesterol-lowering drugs which reduces fats absorption in the intestines. Since vitamin D is a fat-soluble nutrient, reducing fats absorption also lowers vitamin D absorption.14 Phytosterol supplements are plant-derived products that can lower cholesterol, but they also interfere with the absorption of vitamin D and should be taken separately with vitamin D.15 You should consult your doctor for more information on the specific cholesterol or blood pressure lowering drugs that you are prescribed, and how long you should wait to take vitamin D after your medication.
Summary
There have not been any suggested negative effects of consuming iron and vitamin D together. However, it is recommended to consume iron and vitamin D separately because of their different optimum absorption times. If you are unsure of whether certain foods or supplements containing these nutrients can be taken together, make sure to seek advice from your healthcare provider.
References
- Abbaspour N, Hurrell R, Kelishadi R. Review on iron and its importance for human health. J Res Med Sci [Internet]. 2014 Feb [cited 2022 Aug 28];19(2):164–74.
- Puig S, Ramos-Alonso L, Romero AM, Martínez-Pastor MT. The elemental role of iron in DNA synthesis and repair. Metallomics [Internet]. 2017 [cited 2022 Aug 29];9(11):1483–500.
- Kennel KA, Drake MT, Hurley DL. Vitamin d deficiency in adults: when to test and how to treat. Mayo Clin Proc [Internet]. 2010 Aug [cited 2022 Aug 25];85(8):752–8.
- Gordon PL, Sakkas GK, Doyle JW, Shubert T, Johansen KL. The relationship between vitamin d and muscle size and strength in patients on hemodialysis. J Ren Nutr [Internet]. 2007 Nov [cited 2022 Aug 29];17(6):397–407.
- Hewison M. Vitamin D and immune function: an overview. Proceedings of the Nutrition Society [Internet]. 2012 Feb [cited 2022 Aug 29];71(1):50–61.
- Madar AA, Stene LC, Meyer HE, Brekke M, Lagerløv P, Knutsen KV. Effect of vitamin D3 supplementation on iron status: a randomized, double-blind, placebo-controlled trial among ethnic minorities living in Norway. Nutrition Journal [Internet]. 2016 Aug 9 [cited 2022 Aug 27];15(1):74.
- Michelazzo FB, Oliveira JM, Stefanello J, Luzia LA, Rondó PHC. The influence of vitamin a supplementation on iron status. Nutrients [Internet]. 2013 Nov 7 [cited 2022 Aug 29];5(11):4399–413.
- Masoud MS, Alokail MS, Yakout SM, Khattak MNK, AlRehaili MM, Wani K, et al. Vitamin d supplementation modestly reduces serum iron indices of healthy arab adolescents. Nutrients [Internet]. 2018 Dec 2 [cited 2022 Aug 28];10(12):1870.
- Piskin E, Cianciosi D, Gulec S, Tomas M, Capanoglu E. Iron absorption: factors, limitations, and improvement methods. ACS Omega [Internet]. 2022 Jun 21 [cited 2022 Aug 29];7(24):20441–56.
- Kobayashi Y, Wakasugi E, Yasui R, Kuwahata M, Kido Y. Egg yolk protein delays recovery while ovalbumin is useful in recovery from iron deficiency anemia. Nutrients [Internet]. 2015 Jun [cited 2022 Aug 29];7(6):4792–803.
- Alleyne M, Horne MK, Miller JL. Individualized treatment for iron-deficiency anemia in adults. The American Journal of Medicine [Internet]. 2008 Nov 1 [cited 2022 Aug 29];121(11):943–8.
- Johnson-Wimbley TD, Graham DY. Diagnosis and management of iron deficiency anemia in the 21st century. Therap Adv Gastroenterol [Internet]. 2011 May [cited 2022 Aug 29];4(3):177–84.
- Fuzi SFA, Koller D, Bruggraber S, Pereira DI, Dainty JR, Mushtaq S. A 1-h time interval between a meal containing iron and consumption of tea attenuates the inhibitory effects on iron absorption: a controlled trial in a cohort of healthy UK women using a stable iron isotope. The American Journal of Clinical Nutrition. 2017;106(6):1413–21.
- Fratter A, Pellizzato M. Novel micellar system for Vitamin D3 oral delivery: Assessment of enteric absorption through a digestion-like in vitro model. Journal of Drug Delivery Science and Technology [Internet]. 2020 Oct [cited 2022 Aug 29];59:101840.
- Maurya VK, Aggarwal M. Factors influencing the absorption of vitamin D in GIT: an overview. J Food Sci Technol [Internet]. 2017 Nov [cited 2022 Aug 29];54(12):3753–65.
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