ONGOING COLUMNS: Nutrition for the Family
Evaluation of adequate iron intake is an important aspect of prenatal care. Iron is an essential component of hemoglobin. Maternal increases in red blood cell production lead to increases in plasma volume and red cell mass. As a result (in addition to needs of the fetus and placenta), the need for iron is increased during pregnancy. Not meeting this need can lead to iron deficiency anemia (IDA), which can in turn increase risk of complications, including premature and low birthweight infants, low iron stores in the infant, impaired cognitive and behavioral development (National Institutes of Health [NIH], n.d.). Knowledge gained by the mother during pregnancy may confer a lasting benefit on the family's nutritional needs. However, there is confusing and conflicting information about iron absorption and dietary iron sources.
There are two sources of dietary iron, heme and non-heme; each with different bioavailability and are unequally influenced by iron absorption enhancers or inhibitors. Heme iron has the greater bioavailability and is less influenced by other foods. Foods highest in heme iron include lean meat and seafood. Non-heme iron is the form of iron found in plants and iron-fortified foods. Meat, seafood, and poultry contain both heme and non-heme iron. Good sources of non-heme iron include fortified cereals, dark chocolate, tofu, cashews, white beans, chick peas, lentils, and vegetables such as spinach, potatoes, and canned tomatoes. Ascorbic acid (Vitamin C) enhances absorption of non-heme iron, as does meat, seafood, and poultry, whereas some polyphenols found in spinach, cereal and legumes and phytates found in grains and beans inhibit bioavailability. Calcium may reduce bioavailability of both heme and non-heme iron. Milk and cheese contain no iron.
Recommended Dietary Allowances of iron during pregnancy is 27 mg (slightly higher for vegetarians) (NIH, n.d.). A dietary review for adequate iron intake may seem to be straightforward because iron is an aspect of the Food and Drug Administration (FDA) that requires “nutritional facts” labeling. However, daily value (DV) listed on labels is based on the FDA's recommendation of 18 mg, thus making the percentage difficult to calculate for daily adequacy. The FDA has issued a new, more useful labeling rule that will state the actual amount of iron in milligrams; however, it does not go into effect until 2020 or beyond. Some fast food restaurants offer information on iron content, for example, McDonalds lists iron in both DV and in milligrams.
Insufficient iron intake during pregnancy increases likelihood of women developing IDA, so when and should the clinician recommend supplementation? Guidelines vary: Some experts recommend treating IDA (hematocrit less than 33% before 28 weeks; 32% thereafter) with iron supplementation in addition to prenatal vitamin. Others recommend low-dose iron supplement for all women and the United States Preventive Services Task Force states there is insufficient evidence for either routine screening for IDA or supplementation (NIH, n.d.).
If the clinician determines the woman needs supplementation, the next step is choosing the type and amount of supplementation. Iron supplements come in many forms. Prescription prenatal multivitamins can contain anywhere from 18 to 50 mg of iron. Most, but not all, contain calcium, which can interfere with absorption. Higher iron content multivitamins may also contain a stool softener. Over-the-counter prenatal vitamins generally contain 18 mg of iron; gummy prenatal vitamins contain no iron. The most common iron supplements are in the form of ferrous salts such as ferrous sulfate, ferrous gluconate, and ferrous fumarate and each has a different percentage of elemental iron (the amount that will be absorbed). One iron supplement that advertises as being “gradually absorbed with less side effects” contains carbonyl iron. However, this preparation contains lactose—an inappropriate choice for vegan patients. Doses higher than 45 mg of elemental iron may cause nausea or constipation (NIH, n.d.). Some patients may tolerate one iron preparation better than another.
Evaluating iron intake may be a challenge but ensuring iron adequacy is a critical aspect of quality prenatal care. Knowing about dietary iron absorption and individualizing iron supplementation is key.