By analysing the brain tissue of babies suspected of having died of SIDS, Dr Rita Machaalani and Dr Karen Waters from the Faculty of Medicine and the University's Bosch Institute have shown that cigarette smoke induces abnormalities in babies' brains, putting them at greater risk.
They specifically found that any exposure to secondary smoke, not just smoking by the mother during pregnancy, could lead to brain cell changes.
"Passive smoking has long been identified as a risk factor for SID, but the biological mechanisms that lead to death was unknown until now," said Dr Machaalani.
By looking at the post mortems of 67 SIDS infants who died suddenly between 1997 and 2002, they were able to correlate this information with the risk factors associated with SIDS, such as tummy sleeping, sharing a bed with adults and exposure to smoking. This data was taken from information obtained during police interviews with the babies' parents and with hospital records.
"We were able to show that there is cell death in a region of the brain that plays a major role in the control of breathing and heart function in babied who died of SIDS compared to those who died of other causes," said Dr Machaalani.
Of the 67 SIDS babies that were investigated, the researchers found that 81 per cent had been exposed, compared with 58 per cent of non-SIDS infants, and 32 per cent that were in bed with a parent when they died.
"This Australian study is unique as no other study has had access to such a large dataset of brain tissue or the ability to correlate the tissue with the autopsy results and record the risk factors," said Dr Machaalani. "It provides further evidence of increased apoptosis in the brainstem of SIDS infants but shows for the first time these changes are also affected by age and gender, and by clinical risk factors such as sleep position and cigarette smoke exposure," she said.
The findings of the study appear in the most recent issue of Brain and Acta Neuropathologica.