Download G_1883_Iron_10_24_13

Iron
Chief functions
 Involved in red blood cell function
 Integral to many enzymes
 Has a role in the blood and respiratory transport of oxygen and carbon dioxide
 Important part of cellular respiration and energy production
 Involved in immune function
 Involved in cognitive performance
About two-thirds of the iron in the body is found in hemoglobin, which is the protein in red
blood cells that carries oxygen to tissues. Smaller amounts are found in the myoglobin, which
carries oxygen to the muscles.
Deficiency symptoms
 Lethargy
 Weakness
 Decreased ability to perform at work or school
 During childhood—slow cognitive and social development
 Feeling cold all of the time
 Decreased immune function
 Glossitis
 Pica or geophagia
Toxicity symptoms
 Abnormal accumulation of iron in the liver
 Excessive tissue ferritin levels
 Elevated serum transferrin levels
 Oxidation of low-density lipoprotein (LDL) cholesterol
 Cardiovascular complications
Nutrient-nutrient reactions and absorption
 Heme iron, found in hemoglobin, myoglobin, and some enzymes, is absorbed across the brush
border of the intestines via vesicle formation around the heme after animal protein is consumed
 Nonheme iron, found mostly in plant foods, but also found in some animal foods, must enter
the brush border membrane via facilitated diffusion down a concentration gradient, and must
enter the duodenum and upper jejunum in a soluble, ionized form in order transfer across the
brush border
 Among adults with normal hemoglobin levels, between 5% and 15% of ingested heme and
nonheme iron is absorbed
– Individuals with iron deficiency anemia may absorb much more ingested iron—up to 50%,
although this level is rare
– Women who are iron deficient, but not anemic, probably absorb between 20% to 30%
– Between 2% and 10% of nonheme iron in vegetables is absorbed, while 10% to 30% of iron
heme and nonheme from animal sources is absorbed
DRI
mg Tolerable Upper Limits
0-0.5 year
N/D
40
0.5-1 year
6.9
40
1-3 years
3.0
40
4-8 years
4.1
40
Female 9-13 years
5.7
40
Male 9-13 years
5.9
40
Female 14-18 years
7.9
45
Male 14-18 years
7.7
45
Female 19-30 years
8.1
45
Male 19-30 years
6.0
45
Female 31-50 years
8.1
45
Male 31-50 years
6.0
45
Female 51-70 years
5.0
45
Male 51-70 years
6.0
45
Female >70 years
5.0
45
Male >70 years
6.0
45
Pregnant 14-18 years 23.0
45
Pregnant 19-30 years 22.0
45
Pregnant 31-50 years 22.0
45
Lactating 14-18 years 7.0
45
Lactating 19-30 years 6.5
45
Lactating 31-50 years 6.5
45
DRI=Dietary Reference Intakes, mg=milligram, ND=not determined
Dietary sources
 Best:
– Liver
– Seafood
– Kidney
– Heart
– Lean meat
– Poultry
– Dried beans
– Vegetables
 Good:
– Egg yolks
– Dried fruits
– Dark molasses
– Whole-grain and enriched breads
– Cereal
Groups at highest risk for deficiency
 Infants younger than 2 years of age
 Adolescent girls
 Pregnant women
 Women with heavy menstrual losses
 Older adults
 Individuals with increased intestinal motility or steatorrhea
 Individuals with celiac disease or Crohn’s disease
 Individuals with kidney failure, especially those on dialysis
 Individuals who engage in regular, intense exercise are at an increased risk for having
inadequate iron status:
– The need for iron sometimes is 30% higher for these individuals
– Female athletes, runners, and vegetarian athletes are at particularly higher risk
Other facts
 Iron deficiency anemia is the world’s most common nutritional deficiency disease:
– As many as 80% of the world’s population are possibly iron deficient, while 30% may have
iron deficiency anemia
– It is estimated that 12% of all women 12 to 49 years of age in the United States are iron
deficient
– Iron deficiency among lower income pregnant women in the United States is around 30%
 Healthy adult men have approximately 3.6 grams (g) of total body iron and women have
approximately 2.4 g—30% is stored in the liver, 30% in the bone marrow, and the rest in the
spleen and muscles
 Excessive iron intake may contribute to coronary heart disease and cancer risk:
– Iron must tightly bind to protein to prevent it from interacting with oxygen to form
intermediates with the potential to damage cell membranes or degrade DNA
 Chronic inflammation can lead to decreased iron absorption
 Ascorbic acid and sulfur-containing amino acids enhance iron absorption
 The lactoferrin in human milk makes the iron in the milk highly bioavailable
 Achlorhydria, hypochlorhydria, or administration of alkaline substances such as antacids
decrease the absorption of nonheme iron
 Foods with high phytate (found in legumes and whole grains) or tannin (found in tea) content
decrease absorption, while certain proteins found in soybeans also inhibit nonheme iron
absorption
 Adequate calcium intake removes the phosphate, oxalate, and phytate that can combine with
iron and decrease its absorption, but calcium itself consumed along with an iron-rich food will
decrease the absorption of the calcium
 Vitamin A deficiency reduces the body’s ability to utilize stored iron
 Ferrous iron salts (ferrous fumarate, ferrous sulfate, and ferrous gluconate) are the bestabsorbed forms of iron supplements:
– It is recommended that most individuals take their prescribed daily iron supplement in two or
three equally spaced doses
– People should start at half the recommended dose and gradually increase it
 Side effects of iron supplements may include:
– Nausea
– Vomiting
– Constipation
– Diarrhea
– Dark-colored stools
– Abdominal distress
References and recommended readings
Mahan LK, Escott-Stump S, Raymond JL. Krause’s Food and the Nutrition Care Process. 13th
ed. St Louis, MO: Elsevier Saunders; 2012.
National Academy of Sciences. Iron. National Agricultural Library, US Dept of Agriculture Web
site. http://www.nal.usda.gov/fnic/DRI//DRI_Vitamin_A/iron.pdf. Accessed October 24, 2013.
Office of Dietary Supplements. Dietary supplement fact sheet: iron. National Institutes of Health
Web site. http://ods.od.nih.gov/factsheets/Iron-HealthProfessional/. Accessed August 20, 2013.
Contributed by Elaine M. Koontz, RD, LD/N
Review Date 10/13
G-1883