B12 & Iron Together
By Michael R. Peluso, Ph.D. Updated December 27, 2018
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Vitamin B-12 and iron together have a role in your body for maintaining red blood cells and their oxygen-carrying capacity. Iron or vitamin B-12 deficiency may cause anemia -- a reduced number or abnormal form and function of red blood cells. Animal foods are your best natural dietary sources of both iron and vitamin B-12. Iron is a nutrient that can be toxic in excess, and supplements should be used under your doctor's supervision.
Vitamin B-12
Vitamin B-12 is a water-soluble vitamin that your body needs to make healthy red blood cells, which carry oxygen to your body's tissues. Red blood cells require vitamin B-12 to regenerate another B-vitamin called tetrahydrofolate during normal metabolism of the amino acid methionine. With insufficient tetrahydrofolate, the genetic material, or DNA and RNA, in blood cells becomes defective. Many cells die in the bone marrow and those reaching the circulation are enlarged -- a condition called megaloblastic anemia or macrocytic anemia, which can be completely corrected with vitamin B-12 treatment.
Iron and Blood Cells
The mineral iron is an important component of many proteins in your body. For example, iron-containing proteins are involved with oxygen transport through your blood and in your tissues. The majority of all iron in your body is present in hemoglobin -- the oxygen-carrying protein of red blood cells. Iron deficiency is a relatively common nutrient deficiency that develops gradually and can eventually lead to iron-deficiency anemia. Hemoglobin production declines and red blood cells are too small and pale in color. Reduced oxygen-carrying capacity in your blood may cause fatigue and weakness, especially when you are physically active.
The recommended dietary allowance of vitamin B-12 is 2.4 micrograms per day for adult men and women, with 2.6 to 2.8 micrograms recommended during pregnancy and lactation. Fish, meat, poultry, eggs and milk products are your best dietary B-12 sources. It is generally not present in plant foods.
Red meats, poultry and fish also contain a form of iron called heme iron that is more easily absorbed than the nonheme iron that is found in plant foods such as lentils, beans and spinach. The recommended dietary allowance of iron is 8 milligrams per day for adult males and 18 milligrams per day for adult menstruating women.
Anemia Considerations
Pregnant women are particularly susceptible to iron-deficiency anemia. The larger blood volume that includes the fetus and placenta increases the iron requirement to 27 milligrams per day. Consult with your doctor, however, before taking an iron supplement regularly. Excessive iron intake may cause iron overload and tissue damage, especially to your liver.
A condition called pernicious anemia can produce a vitamin B-12 and red blood cell deficiency, regardless of your dietary B-12 intake level. In pernicious anemia, your stomach gastric glands do not produce enough of a protein called intrinsic factor, which is required for B-12 absorption. The anemia can be treated with vitamin B-12 injections at your doctor's office.
Present Knowledge in Nutrition, 10th Edition; John W. Erdman Jr. et al.
National Institutes of Health – Office of Dietary Supplements: Iron
Understanding Nutrition, 12th Edition; Ellie Whitney and Sharon Rady Rolfes
National Institutes of Health – Office of Dietary Supplements: Vitamin B12
MedlinePlus: Pernicious Anemia
Michael Peluso is a semi-retired scientist in the field of nutritional biochemistry. He received his M.S. in nutrition from the University of California, Davis and Ph.D. in nutrition from the University of Missouri. Peluso's work has appeared in scholarly publications such as the "Journal of Nutrition," "Lipids" and "Experimental Biology and Medicine."
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