A new study on cholesterol lowering drugs may have solved the riddle of why they're linked with a higher incidence of death by violence: they appear to increase depression.

Researchers from the University of California at San Diego, examining the link between cholesterol and depression in 1000 Californian men over 70, found that depression was three times more common in the group with a plasma cholesterol below 4.14 mmol/L than in the control group with higher levels.

What's more, the University of California researchers found that the extent of depression correlated with the level of cholesterol: the lower the cholesterol level, the more depressed the patient.

This new study was also supported by a letter in the same issue describing depressive illness in four women given the cholesterol lowering drug simvastatin.

"Our finding that lower plasma cholesterol is associated with depressive symptoms in elderly men is compatible with observations that a very low total cholesterol may be related to suicide and violent death," the report said.

The "observations" are a number of recent studies showing that those on cholesterol lowering diet and drugs had a higher incidence of suicide and violent deaths than controls (See WDDTY vol 3 no 12).

The association appeared to be age dependent, since there has been no positive relationship between violence and cholesterol drugs among younger people.

A number of other researchers who have attempted an explanation of the relationship between low cholesterol and violence say that it may have to do with the fact that a decrease in cholesterol leads to a decrease in the level of brain serotonin concentrations, which is linked both to depression and aggression.

Significantly, both behaviours have been reported in some patients taking fluoxetine, the new style anti depressive drug, which supposedly raises the levels of serotonin by slowing the passage of this neurohormone into the cells of the nervous system. It may well be that we don't yet understand the interrelation of hormonal messages that the brain receives and what dietary requirements are necessary to maintain them.

The report concluded that cholesterol lowering should be restricted to individuals at high risk of coronary heart disease.