African Americans who are carriers of the sickle cell trait (SCT) aren’t less fit and are not at greater risk of developing hypertension, diabetes, or metabolic syndrome as they reach middle age compared to non-carriers, new research shows.
The study, “Longitudinal association among sickle cell trait, fitness, and cardiovascular disease risk factors in African Americans in CARDIA,” is published in the journal Blood.
“We sought to understand if having sickle cell trait has an effect on someone’s baseline fitness levels or changes in their fitness over time,” Robert I. Liem, MD, director of the comprehensive sickle cell program and associate professor of pediatrics at Northwestern University Feinberg School of Medicine, said in a news release.
“Based on our findings, there is no evidence that carriers of sickle cell trait are less fit or become less fit with time compared to people who do not have sickle cell trait.”
According to the American Society of Hematology, sickle cell trait is an inherited blood disorder that affects 1 million to 3 million Americans and 8 to 10 percent of African Americans.
Unlike sickle cell disease, a serious illness in which patients have two abnormal copies of the gene, causing the production of abnormal hemoglobin (the substance in red blood cells that helps carry oxygen), individuals with SCT carry only one defective gene copy and typically live normal lives. But evidence from recent studies suggests sickle cell trait carriers may be at higher risk for chronic kidney disease, thrombosis, stroke, and pregnancy-related complications.
In rare cases, some individuals with sickle cell trait who were engaged in high-intensity physical activity were found to have health issues, including sudden death, leading to the National Collegiate Athletic Association to require carrier status testing among all student athletes.
Liem and colleagues evaluated the association of SCT status with cross-sectional and longitudinal changes in fitness and risk of hypertension, diabetes, and metabolic syndrome over 25 years among 1,995 African Americans taking part in the Coronary Artery Risk Development in Young Adults (CARDIA) study.
Among all CARDIA study participants, the prevalence of SCT was 6.8 percent (136 people). Mean age was 24.8 years for those with SCT and 24.3 years for those without SCT (1,859 individuals). The prevalence of baseline hypertension, diabetes, and metabolic syndrome was similar between SCT carriers and non-carriers.
Compared to participants without SCT, participants with SCT had similar baseline measures of fitness, including exercise duration (540 seconds vs. 535 seconds); estimated METs (metabolic equivalent, a measure expressing the energy cost of physical activities, 11.7 units vs. 11.6 units); maximum heart rate (175 bpm vs. 174 bpm); and heart rate at two minutes recovery (43 bpm vs. 44 bpm).
After adjusting the data for sex, baseline age, BMI, fitness and physical activity, researchers found there was neither an association of SCT status with longitudinal changes in fitness nor an association with development of hypertension, diabetes or metabolic syndrome over 25 years of testing.
“Although this study examined fitness levels in adults with sickle cell trait, it did not specifically evaluate exercise safety,” Liem said about the study limitations.
“From what we know from other studies, however, it is recommended that people with sickle cell trait who exercise, especially competitive and elite-level athletes, remain hydrated and know the symptoms of exertion-related rhabdomyolysis, a condition that causes the breakdown of muscles and has been associated with sickle cell trait. It is also important to make others aware of those symptoms,” he added.