Research has suggested that the ban on openly gay personnel serving in the US military may be lowering performance to life-threatening levels.

The study, from Cornell University, found that gay and lesbian participants who were told to conceal their sexual orientation performed 20 per cent worse on spatial reasoning tests and 50 per cent worse on physical endurance tests than gay and lesbian subjects who were not given this order.

Previous studies have suggested that gay and lesbian personnel may receive less medical or psychological care due to fears of revealing their sexuality, but the study’s authors say this is the first research to find a link between the policy and relevant tasks.

The gay ban allows gays and lesbians to serve in the military, but only if they keep their sexual orientation secret.

“It directly counters this argument that ‘Don’t Ask, Don’t Tell’ allows us to have the highest-performing individuals,” Clayton Critcher, one of the study’s authors, told The Advocate. “It affects everyone around them and the general quality of performance.”

The researchers asked subjects to hold an eight to ten-minute conversation but to keep their sexuality quiet. They were then asked to complete a spatial reasoning test based on an Army intelligence test and to hold an exercise grip as long as possible.

While those who had concealed their sexuality were able to hold the exercise grip for an average of 11 seconds, the control group held it for an average of 23 seconds. The group asked to hide their sexuality also scored 20 per cent worse on the spatial reasoning test than the participants who were allowed to speak about their sexuality.

It was found that the effect was clear even if the participants talked about subjects completely unrelated to relationships or family life.

The researchers stressed that the effect was not due to “mental anguish” caused by hiding sexuality. Rather, they argued that hiding it requires monitoring one’s actions and social environment, which leads to depleted mental resources.

They suggested thinking of the mind in terms of a battery, so those who used mental resources to hide their sexuality subsequently performed worse on tests, even those which required physical endurance as mental resources are still needed to continue.