A study in the Journal of the American Medical Association compared autopsy results of babies who died of SIDS with those who died of other causes. They found many SIDS babies had lower levels of a chemical called serotonin in their brain stems. This is the part of the brain that controls sleep and breathing.
It is possible the infants had difficulty regulating their heartbeat and breathing during sleep.
There is no test for serotonin deficiency, but researchers hope to find out more about its possible link.
