People who carry a gene for sickle cell disease might not have an elevated mortality risk, according to a study released today in the New England Journal of Medicine.

Sickle cell disease occurs in 1 out of every 365 black people born in America, according to the Centers for Disease Control and Prevention. They carry two copies of a gene for sickle cell disease. Those who carry only one copy of the gene are said to have sickle cell trait. About 1 in 13 black Americans have sickle cell trait. An earlier study found that sickle cell trait may lead to an increased risk of sudden death, but the new study comes to a different conclusion.

Sickle cell disease causes red blood cells to be misshapen and can lead to lifelong pain and a reduced lifespan. It wasn't clear whether sickle cell trait is dangerous.

Researchers at Stanford University Medical Center found that there seemed to be no significant difference in death risk for people with sickle cell trait compared to those without it. However, carriers of the sickle cell trait were more likely to develop exertional rhabdomyolysis, a breakdown of skeletal muscle tissue caused by strenuous exercise.

Stanford researchers reviewed the health records of 47,944 black soldiers with known sickle cell status who served between 2011 and 2014. The records were from the Stanford Military Data Repository data set, a digital archive of health encounters at military and civilian medical institutions. The records also include basic health information and certified records of physical performance and mortality of all active duty U.S. Army soldiers.

Gender, age and lifestyle factors also affected who experienced exertional rhabdomyolysis. Women had a significantly lower rate compared to men, and soldiers over 36 saw a 57 percent heightened risk for exertional distress. Risk for exercise-related muscle breakdown was also significantly higher in soldiers who had obesity, smoked or took anti-psychotic drugs.

Lianne Kurina, one of the lead researchers of the study, said the findings could indicate that perhaps the focus shouldn’t be on sickle cell trait, but other factors that lead to rhabdomyolysis. “There are a lot of factors that should be considered,” she said. “Sickle cell trait is a non-modifiable risk factor. Some of these factors are modifiable.”

Rakhi Naik, a certified hematologist at Johns Hopkins School of Medicine, said that the study’s findings are exciting.

“One thing that’s the most important is that there have been these mandated screenings” for sickle cell trait, she said. The Army, Navy and NCAA now test for sickle cell trait. People who test positive for the gene are warned against dehydration and overheating. “The major point of this study is that it seems that the risk of death can be completely eliminated by hydration.”

Kurina also said that increased awareness about hydration and overheating might have contributed to the reason why there isn't an increase in mortality among soldiers with sickle cell trait.

She hopes the research will also promote further discussion about screening for sickle cell trait.

A 1987 study reported a 2,800 percent increase in the risk of exertion-induced sudden deaths among black recruits thought to have sickle cell trait. That study helped lead to more screening. The new study pointed out that the sickle cell status of every person in the past study wasn’t known.

Kurina said knowing the sickle cell status of everyone involved in her research was crucial to her team’s findings. “This is really the first time where people have this population where high numbers of people have been tested,” she said.