Spinach has been grown in Asia for so many centuries that its origins predate existing records. Even if scholars and spinach experts aren't able to pinpoint the exact birthplace of this vegetable, one thing is certain: If there were an award for lifetime achievement, spinach would definitely be in the running. By the 1400s, spinach had made its way throughout Asia where it became a mainstay of many European menus. Today, it's a multi-faceted green eaten worldwide in everything from casseroles and pastas to soups and salads [source: Colorado State University].
Currently, China produces about 85 percent of the world's supply of spinach, followed by the United States, which harvested 280,000 metric tons (618,000 pounds) of spinach in 2011 alone [source: Borris]. By far the largest U.S. spinach producer is California, trailed by Arizona, New Jersey and Texas [source: USDA].
The controversy surrounding the amount of iron in this leafy green centers on a report made in 1972 by a nutritionist. Professor Arnold Bender asserted that 19th century German researchers made an error when recording spinach's iron content by placing the decimal point in the wrong position, accidentally multiplying spinach's iron content by 10. The story, which contended spinach had no more iron than other common vegetables, was perpetuated as fact in medical journals, textbooks and popular culture for more than 30 years until it was proven incorrect in a meticulously researched article by criminologist Mike Sutton. Sutton concluded that these German researchers never existed [source: Kruszelnicki, Sutton].
So what's the truth about spinach's iron content? According to the USDA, there are:
- 6.43 milligrams in one cup cooked fresh spinach
- 4.92 milligrams in one cup canned spinach
- 3.72 milligrams in one cup frozen spinach
- .81 milligrams in one cup raw spinach
One cup of cooked fresh spinach contains about one milligram more iron than you'll find in 3 ounces (85 grams) of beef liver, which has long been known for its iron content. And far more than you'd encounter in a head of lettuce. In fact, you'd need to eat the entire head of lettuce to gain just 2.02 milligrams of iron, a fraction of what you'll find in spinach [source: USDA].
However, spinach also contains oxalic acid which inhibits iron absorption. So it's good to eat it with foods that enhance iron absorption like meat, fish, poultry, citrus fruits or certain vegetables like broccoli, sweet peppers, tomatoes and potatoes [source: Tsang].