About 300 babies a year die from cot death
More evidence has emerged that a chemical imbalance in the brain may play a key role in cot deaths.
Researchers found low levels of serotonin triggered changes in heart rate and body temperature that led to sudden death in tests on mice.
Serotonin is a neurotransmitter that passes messages between brain cells and is most associated with mood.
The research, by the European Molecular Biology Laboratory in Italy, follows similar findings in 2006 in the US.
About 300 babies die suddenly each year in the UK, although numbers have fallen by 75% since the early 1990s when a public campaign was launched to reduce the risks.
In the latest study, published in the journal Science, mice susceptible to sudden death had been engineered to slow the production of serotonin.
This affected the brain stem which is linked to the spinal cord and helps control the lungs and heart.
Study leader Dr Cornelius Gross said: "At first sight the mice were normal.
"But then they suffered sporadic and unpredictable drops in heart rate and body temperature.
"More than half of the mice eventually died of these crises during a restricted period of early life."
A spokeswoman for the Foundation for the Study of Infant Deaths said it "reinforced" the findings from two years ago.
But she added: "What we need now is more research to find out what causes the serotonin imbalance - genetic factors or environmental?"