England's NHS screening programme has been rewriting its leaflet for patients after concerns it did not provide enough explanation for women about their choices.
A new version of the leaflet will be published by this summer.
Richard Winder, deputy director of NHS cancer screening programmes, said: "There is a risk of over-diagnosis, and possible subsequent over-treatment, associated with any screening programme.
"But this latest, independent study shows that the risk of over-diagnosis is very much lower than some other recent estimates have claimed, and that the benefits far outweigh the risks."
Sara Hiom of Cancer Research UK says she hoped the latest study would reassure women that screening was valuable.
"What we need to remember of course is that detecting cancers earlier generally means improved survival. And we know through trials and through research that breast screening can save lives," she said.
Emma Pennery, clinical director at Breast Cancer Care, said it was aware the ongoing debate over the effectiveness of screening could cause "confusion and anxiety for women".
"This robust study clearly reinforces that screening remains an effective option for detecting breast cancers," she said.
However, Jayant Vaidya, a breast cancer surgeon at University College London and the Whittington Hospital, said the study was based on calculations that were opaque.
"Women who go for breast cancer screening need to know that there's a good chance they could be diagnosed with a cancer which is not harmful and may never have bothered them," he said.
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