A person's blood type is determined by the antigens in his blood, chemical substances that the immune system might react to if he were given a transfusion of the wrong blood, according to the Red Cross 1. The main blood type groupings include A, B, AB and O 1. Each can be either negative or positive. Your blood type affects who you can give or receive blood from, and it may even affect your diet 1. O positive blood is by far the most common blood type 1.

Most Common Type

O positive blood occurs most commonly in Hispanic people (53%, according to the Red Cross), and to a slightly lesser extent in African-American people, and it occurs more than any other blood type in people of Asian and European descent as well (http://www.givelife2.org/aboutblood/bloodtypes.asp) 1. According to www.bloodbook.com, almost 40 percent of the population has O positive blood. This makes it the most common blood type, and therefore the most in demand 1. You can learn your type by donating blood, by paying to have a test done by your doctor, or by taking a home blood typing test 1. By knowing your blood type and carrying this information with you, you will be prepared in case you ever need an emergency blood transfusion 1.

Blood Transfusions

A donor and patient must have compatible blood types for a transfusion to work. If they do not have compatible blood types, complications such as clotting can occur in the patient, as her immune system responds to what it recognizes as a foreign object. People with O positive blood can receive O positive or negative donations. They can donate to people with O positive, A positive, B positive or AB positive blood.

Determining Factors

A mother and father's blood types determine their baby's blood type 1. According to the University of Utah's Genetic Science Learning Center, if the mother and father have type O blood, their child will have type O blood as well 1.

Health Considerations

A person's blood type may affect how he processes food 1. Many people such as Dr. Peter J. D'Adamo, creator of "The Blood Type Diet," have theorized that blood type affects a person's nutritional needs 1. People with O positive blood often have difficulty processing wheat gluten, according to this theory, resulting in weight gain and improper nutrition.

Additional Considerations

People of all blood types should donate blood, if possible, whether they have a common or rare blood type 1. Doing this will help to ensure that they, their loved ones, and others will have a supply of blood if and when they need it.