But simply having low levels of serotonin is insufficient as a predictor.
"It has more to do with the predisposition to suicide than to generating suicidal behavior," said Mann. "Serotonin is detectable and independent of timing. So by evaluating the function of the serotonin system, we can identify who is vulnerable and plan more specific pharmacological intervention."
Mann said serotonin indexes which have been employed in the lab include the cerebrospinal fluid level of 5-hydroxyindoleacetic acid, prolactin response to serotonin agonists-such as fenfluramine hydrochloride (Pondimin)-and platelet serotonin-related proteins or serotonin content (Mann and others, 1992).
Said Mann, "Three different measures of serotonin function-completely unrelated approaches-all show the same thing, mainly a deficiency in patients with a history for more lethal suicide attempts."
Now, Mann and his group are looking at imaging of serotonin responses in the brains of patients, using positron emission tomography (PET).
So what causes serotonin deficiency?
"Genetics are an important area, but there are some environmental factors that increase or decrease serotonergic activity," he said, listing factors such as genetics, diet, drugs and alcohol(Drug information on alcohol), gender and age.
For instance, lowering and raising cholesterol levels in monkeys significantly lowers and raises serotonin activity. So although lowering levels in humans does reduce heart attacks, it may raise the risk of dying from other causes, including suicide.