Important US research to reduce HIV infection may have been prevented in recent years because scientists have censored their funding requests in response to political controversy, according to a study published on Tuesday.

    Writing in PLoS Medicine, the academic journal, Joanna Kempner from Rutgers University identified a "chilling effect" on researchers seeking grants from the government-backed National Institutes of Health after their work was questioned by Republican lawmakers and Christian groups.

    The findings suggest politics influence scientists' willingness to conduct research, and raise warnings at a time of continued sensitivity over medical research topics from sexual behaviour to stem cells.

    Among 82 researchers polled by Ms Kempner, who had received money from the NIH, almost a quarter had dropped or reframed studies around sexual behaviour they judged to be politically sensitive, and four had made career changes and left academia as a result of the controversy.

    Half reframed their studies to avoid work on marginalised populations, or dropped studies they thought would be politically sensitive, such as those on sexual orientation, abortion, childhood sexual abuse, and condom use. One interviewee said: "I do not study sex workers, I study 'women at risk'."

    Almost four-fifths believed NIH funding decisions had become more political under President George W. Bush than under his predecessor Bill Clinton, and more than a third believed they were less likely to receive NIH funding as a result of the controversy.

    Ms Kempner, an assistant professor of sociology, quizzed scientists who had been drawn into a 2003 debate when Patrick Toomey, the Republican Representative, called for the NIH to rescind a series of grants for studies on sexuality, sparking joint House and Senate hearings and a review by the NIH.

    The NIH ultimately stood by the grants it had given as scientifically sound, however, Ms Kempner's research identified widespread self-censorship among the recipients after the debate.

    Most researchers who "gamed" the system by removing sensitive words in their grant applications – sometimes encouraged by sympathetic grants officers in the NIH – claimed any changes they made were cosmetic.

    But some argued that the consequence was to change the focus of their research, and still more warned that obscuring the contents of their work made it more difficult for others to subsequently identify and use their findings in database searches.

    A quarter said they sought funding from other sources, and 10 per cent said the controversy had only strengthened their commitment to continue their research.