B-12 and Iron Absorption

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Iron and vitamin B-12 facilitate critical functions in the body, so their absorption is crucial to prevent deficiencies and illnesses. Several factors can negatively affect absorption. Calcium and other nutrients can have a poor effect on iron absorption, and certain medications and medical diagnoses can inhibit B-12 absorption.


There are two types of iron: heme and non-heme. Heme iron is derived from animal sources, from which the body absorbs between 15 and 35 percent. Non-heme iron comes from plant sources, and only 2 to 20 percent is absorbed by the body. The absorption rate of iron is highest when body stores are low. Vitamin C and meat proteins encourage the absorption of non-heme iron. Calcium, tannins, phytates and fiber may inhibit the absorption of non-heme iron.


Vitamin B-12 is found in animal products such as meat, eggs, dairy and poultry. Medical conditions that interfere with food absorption, such as weight loss surgery, gastritis, celiac or Crohn’s disease, can cause B-12 deficiency. Stomach acid is necessary for the absorption of B-12, so a lack of acid due to aging or commonly prescribed heart burn medications can hinder B-12 absorption. Medications, including antibiotics such as tetracycline, can also interfere with absorption.

Recommended Intakes

According to the National Institutes of Health, menstruating girls aged 14 to 18 require 15 milligrams of iron per day, and menstruating women aged 19 to 50 require 18 milligrams of iron per day. Boys aged 14 to 18 need 11 milligrams of iron per day and men aged 19 to 50 need 8 milligrams of iron per day. Vitamin C assists the absorption of iron when they are taken together. Sources of vitamin C include oranges, green peppers, strawberries and broccoli. The National Institutes of Health also recommends 2.4 micrograms of B-12 daily for individuals 14 years of age and older. Dietary sources of iron and B-12 include beef, chicken, tuna, pork, spinach, beans and lentils.


Malabsorption of iron or vitamin B-12 can lead to deficiencies which can develop gradually or intensify quickly. Symptoms of B-12 deficiency include numbness, weakness, anemia, difficulty walking, cognitive impairment and jaundice. Vitamin B-12 deficiency treatment depends on the cause. Pernicious anemia, in which the body lacks the ability to absorb the vitamin, can be treated with a B-12 injection. Iron deficiencies are generally associated with an imbalanced diet, blood loss or malabsorption. Symptoms of iron deficiency include weakness, cognitive impairment and poor immune function. An oral supplement or an injection may help correct a low iron level. Consult a physician before beginning an iron or vitamin B-12 supplement regimen.