Sickle cell anemia affects about 72,000 people in the United States. Most Americans who have sickle cell anemia are of African descent. The disease also affects Americans from the Caribbean, Central America, and parts of South America, Turkey, Greece, Italy, the Middle East and East India. Sickle-cell disease and the associated trait are most prevalent in Africa and Central America, which is attributed to natural selection:  the sickle-cell trait confers a survival advantage in areas with a high occurrence of malaria, which has a high death rate among individuals without the trait.There also have been studies that show changes in the globin genes. There have been noted changes in the beta-globin sequence, to what is known as the sickle hemoglobin. The significance of the sickle-cell trait is that it does not show any symptoms, nor does it cause any major difference in blood cell count. The trait confers about 30% protection against malaria and its occurrence appears to have risen tremendously in Africa, India and the Middle East. Some findings also show the reduction of the sickle-cell trait in those who retain much more fetal hemoglobin than usual in adulthood. Fetal hemoglobin likely plays a role in the prevention of sickling. Elevated fetal hemoglobin levels have been observed in populations where sickle-cell disease is prevalent. Whole genome sequence analysis has identified a single origin of the sickle trait, with one haplotype ancestral to all sickle-cell variants. This haplotype is thought to have originated in the Sahara during the Holocene Wet Phase around 7,300 years ago.
Individuals with known positive sickle cell trait status experiencing significant muscle weakness or fatigue during exercise should take extra time to recover and hydrate before returning to activity in order to prevent further symptoms.A collapse can be prevented by taking steps to ensure sufficient oxygen levels in the blood. Among these preventative measures are proper hydration and gradual acclimation to conditions such as heat, humidity, and decreased air pressure due to higher altitude. Gradual progression of exertion levels also helps athletes bodies adjust and compensate, gaining fitness slowly over the course of several weeks. See also
Ryan Clark (American football)

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