Low IQ and mental-health problems

There is increasing evidence that children and adolescents who score lower on intelligence tests may be more vulnerable to mental-health problems later in life. However, much of the evidence is based on individuals whose disorders were severe enough to require admission to hospital. A study of 3,258 men whose intelligence was measured during their military service and whose mental health was assessed when they reached middle age has found that lower cognitive ability was associated with an increased risk of a number of mental-health problems

Mental-health problem	Odds of developing it (1 = average risk, 2= double the risk) for people of lower IQ
Any mental-health problem	1.32
Depression	1.43
Anxiety	1.2
Alcohol abuse or dependence	1.39
Post-traumatic stress disorder (PTSD)	2.5

The association between lower IQ and mental-health problems remained statistically significant even after a number of other factors had been taken into account.

Gale, Catharine R. ... [et al] - Cognitive ability in early adulthood and risk of 5 specific psychiatric disorders in middle age Archives of General Psychiatry December 2008, 65 (12), 1410-1418