Some cross sectional studies show an association between low serum cholesterol concentration and depression,
12 and, given this, there is also an association between low serum cholesterol and suicide.
8 But the associations may arise because low serum cholesterol causes depression or because it is a consequence of depression (simply because depressed people eat less). Cross sectional studies cannot determine which is the cause and which the consequence. Other observational evidence indicates that the low cholesterol concentration is a consequence of the depression since (a) there was no excess mortality with low serum cholesterol in prospective studies of working men (less likely to have serious psychiatric illness on entry to the studies by virtue of being in work),
8 (b) the excess mortality in the prospective studies was short term with no significant excess after six years,
8 and (c) treating depression has been shown to increase serum cholesterol concentration.
13 The recent observational studies have merely introduced variations on the same theme: low serotonin concentrations (which accompany and may cause depression) are, not surprisingly, also associated with low cholesterol,
2 14 people who attempt suicide have low serum cholesterol concentrations,
3 and, in this week's issue, men with declining serum cholesterol concentrations are particularly likely to commit suicide.
1 If these were the only studies one could not distinguish cause from consequence.
The randomised trials resolve the matter, providing compelling evidence that low cholesterol concentration does not cause depression, accidents, or suicide.