Chow Line: If you must, use math to figure iron intake (for 4/1/07)

March 23, 2007

I am a 51-year-old woman trying to track my iron intake, but nutrition labels only give a percentage "Daily Value" for iron. How can I tell how much iron a food really contains?

You raise a good question. The Daily Value information on Nutrition Facts labels was designed to simplify nutrition information. But that makes it a challenge for people like you who want more details.

The Daily Values on Nutrition Facts labels are based on the old U.S. Recommended Daily Allowances established by the National Academy of Sciences in 1968. In this case, 100 percent of the Daily Value of iron is 18 milligrams. So, if a label indicates a serving of the food contains 10 percent of the Daily Value of iron, it contains about 1.8 milligrams.

The label couldn't really use newer recommendations (known as Dietary Reference Intakes), because the recommended amounts change depending on a person's sex or age. The people who designed the Nutrition Facts label wanted to keep the message uncomplicated, and using the RDAs was the solution they decided upon.

You may already know that 18 milligrams of iron is the amount recommended for women ages 19 through 50. But the recommended amount varies for different people. Here are the Dietary Reference Intake recommendations for iron for all groups:

  • Infants from 7-12 months, 11 mg.
  • Children ages 1-3, 7 mg.
  • Children ages 4-8, 10 mg.
  • Children ages 9-13, 8 mg.
  • Young men ages 14-18, 11 mg.
  • Young women ages 14-18, 15 mg.
  • Men ages 19-70+, 8 mg.
  • Women ages 19-50, 18 mg.
  • Women ages 51-70+, 8 mg.
  • Pregnant women, 27 mg.
  • Lactating women ages 14-18, 10 mg; ages ages 19-50, 9 mg.

Once you know the recommended amount for your age group, you need to do some math to use the Daily Values on Nutrition Facts labels. In your case (a woman over age 50), divide your recommended amount of iron (8 mg.) by the amount used for the Daily Value (18 mg.), and you get 44 percent. Now, you can just add up the Daily Value percentages for iron on the labels of the foods you eat. When you reach 44 percent, you know you've reached your recommended iron intake for the day.

While most people wonder if they get enough iron, it is possible to get too much. The upper tolerable intake of iron for anyone 14 years and older is 45 milligrams a day, or 2.5 times the Daily Value listed on the label. The upper limit for children is 40 milligrams a day.

Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH, 43210-1044, or filipic.3@cfaes.osu.edu.

Editor: This column was reviewed by Lydia Medeiros, registered dietitian, food safety specialist for Ohio State University Extension, and associate professor in the Department of Human Nutrition, College of Education and Human Ecology.

To receive a PDF file of Chow Line via e-mail, contact Martha Filipic at filipic.3@cfaes.osu.edu.

Author(s): 
Martha Filipic
Source(s): 
Lydia Medeiros