The difference between an A or B in school could boil down to being fit and having normal iron levels, according to researchers at Pennsylvania State University and the University of Nebraska-Lincoln.

Their study found that college students who were fit and had normal iron levels had higher grade point averages than unfit women who were deficient in iron. The difference in grade point average was enough to drop or increase a letter grade.

"GPA is a very easy measure of success and something everyone can relate to," said Karsten Koehler, assistant professor of nutrition and health sciences at Nebraska. "That's something that resonates pretty well."

The 105 women in the study were all enrolled at Penn State, and had an average GPA of 3.68. Data showed that women with the highest levels of stored iron had the highest grades.

In addition, those who were the most fit and also had adequate iron stores had higher grades than less-fit women with lower iron stores.

Adequate iron levels are essential because iron is vital in transporting oxygen from the lungs to tissues throughout the body, and low levels can cause anemia.

A deficiency is linked to fatigue, lower work capacity, and poor academic performance. Physical fitness is also known to influence overall health, cognition and learning.

"It's always nice to show an association that has a meaningful effect that translates into something everybody can apply," Koehler said.

The study was published in The Journal of Nutrition.

Iron deficiency has been linked to other problems. Dermatologists at Cleveland Clinic link iron deficiency, with or without anemia, with hair loss, and have found that treating iron deficiencies can maximize patients' ability to regrow hair.

Research has also shown that eating iron-rich foods like steak and spinach could slash your risk of developing Alzheimer's. An 11-year study from the University of California, San Francisco, found that older adults who had anemia at the beginning of the study were 41 percent more likely to develop dementia than those who had normal iron levels. Red blood cells carry oxygen throughout the body.

Scientists theorize when a person is anemic, brain cells get less oxygen, which damages neurons and leads to a reduction in memory and overall mental decline. "Anemia is common in the elderly and occurs in up to 23 percent of adults ages 65 and older,” said study author Dr. Kristine Yaffe.

Iron-rich foods include red meat, dark leafy greens, whole grains, eggs, and oysters. Iron tablets are available over-the-counter as well as by prescription.