Blood donors are a critical component of our medical system. An adequate supply of blood is essential for the treatment of medical problems ranging from severe accidents to cancer and even extreme anemia due to disease or a poor diet. In these conditions, a blood transfusion can make the difference between life and death.

Keeping donors healthy requires good nutrition. The main issue is replenishing the iron lost from the body in a blood donation.

The average healthy person can easily tolerate this loss, but frequent blood donors and those with diets too low in iron can develop such low iron status that they experience serious health problems. Some of the classic symptoms of low iron include fatigue, depression, sleep problems, difficulty concentrating, hair thinning and fingernail changes.

Question: How much iron is lost in a blood donation?

Answer: The typical 1-pint blood donation contains about 250 mg of iron. That is about 10 percent of the total iron in the body of a healthy woman and 6 percent of the iron in a man. Since men have about three times more iron reserves than women, men can handle blood donations better.

Q: How long does it take to replenish the iron lost in a blood donation?

A: The answer depends on how much iron is in the diet, what types of food contain that iron, and what other types of food are in the diet that might inhibit or promote the intestinal absorption of the iron. Unfortunately, there is more misinformation than reliable information on websites providing guidance about food sources of iron.

A study that provided supplements containing 20 mg of iron per day found that it was enough to replenish the iron in male donors in about two months and in females in about 3 months. This supplement was taken along with a diet containing a normal amount of iron.

Q: What are good food sources of iron?

A: Simple lists of how much iron is in food do not take into account how poorly the human body absorbs iron from some food. These lists are worthless without some understanding of bioavailability — how well iron is absorbed from each food.

Red meats contain well-absorbed iron in a form called heme iron. Animal foods also contain non-heme iron, the only form of iron in plant foods. Human intestines have two separate absorption mechanisms for these forms of iron. The one for heme iron is much more efficient.

For example, a half-cup of cooked spinach and 3 ounces of cooked lean beef contain similar amounts of iron, but the body absorbs about 10 times as much iron from the beef. So, it really takes five cups of cooked spinach to match 3 ounces of beef.

It also helps to know what foods can promote or inhibit the absorption of iron from food. Enhancers of iron absorption include vitamin C and meat in the same meal. Inhibitors include calcium (dairy products, calcium fortified foods and supplements), tannins (tea, coffee and red wine), oxalates (spinach, taro leaf and quinoa) and phytates (whole grains and legumes).

The recommended daily iron intake for a pre-menopausal women is 18 mg if her daily diet includes about 3 ounces of foods providing heme iron. This increases to 33 mg for a vegetarian diet with no heme iron.

The recommendation for men and post-menopausal women is 8 or 13 mg with a vegetarian diet. After a blood donation, add another 20 mg of iron from a supplement to get iron back up to normal.

Alan Titchenal, Ph.D., C.N.S., and Joannie Dobbs, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii-Manoa. Dobbs also works with University Health Services.