However antibiotics were found not to be necessary to reduce the risk for serious complications for upper respiratory tract infections, otitis media or sore throats.
The findings come from analysis of data from 162 GP practices across the UK from 1991 to 2001. Over this time, 3.36 million cases of respiratory tract infection were noted. The researchers then focused on 749,389 recorded episodes of chest infection and the risk of developing serious complications in the month after the infection had been diagnosed.
This showed that although the risk of pneumonia in the month after diagnosis was high, it could be reduced with antibiotics. Without an antibiotic prescription, 4 per cent of those aged 65 and over were diagnosed with pneumonia in the month after a chest infection was diagnosed, compared with 1.5 per cent of those given an antibiotic.
The risk of serious complications after upper respiratory tract infections, otitis media or sore throats was found to be low. But the number of courses of antibiotic needed to prevent one serious complication was high - at over 4,000.
Previous research has raised concerns that GP prescribing of antibiotics could boost rates of antibiotic-resistant bacteria.
Lead researcher Dr Andrew Hayward, from the department of infectious disease epidemiology at University College London, said that the study proved antibiotics were important in reducing the risk of pneumonia in those with chest infections.
'GPs prescribe to around 80 per cent of patients consulting with chest infection even though current guidance suggests that this is unnecessary,' he said.
'This research indicates that GPs may be justified in their decisions to prescribe antibiotics for chest infections.'
However, prescribing for other respiratory tract infections is unnecessary, Dr Hayward added.
'The study does not justify high prescribing levels because around half of the antibiotics prescribed for respiratory tract infections are for sore throats and otitis media.'