For those with poorer health, the burden encountered in diagnosis and treatment procedures is more likely to outweigh the benefits of earlier detection, researchers found.
The findings come one month after the NHS Bowel Screening Programme extended by five years the upper limit at which people are invited for screening.
The £76.2 million a year scheme now offers faecal occult blood testing (FOBT) to all men and women aged 60-75, although anyone older than this can request a kit.
A team led by Dr Christine Kistler of the University of North Carolina at Chapel Hill followed 212 patients aged 70-89 with a positive FOBT result. They examined life expectancy and the health burden for seven years after positive test results.
More than half of the patients underwent colonoscopy, which detected 34 adenomas and six cancers. A quarter of patients who had colonoscopy but did not have cancer still had to undergo three or more tests over seven years.
Nearly half of those without colonoscopy died of other causes within five years.
The authors said their study argued against 'one size fits all' screening and in favour of more specific targeting of FOBT-led screening.
Richard Winder, deputy director of the NHS Cancer Screening Programmes, said: 'Current policy is to screen all eligible asymptomatic people equally.' He added: 'Data from other screening programmes show that screening reduces inequalities between affluent and deprived communities, thus improving overall outcomes.'