Table 2.

Environmental risks that have been most commonly been studied in relation to attention deficit hyperactivity disorder

Pre- and perinatal factors	Environmental toxins	Dietary factors	Psychosocial adversity
Maternal smoking, alcohol and substance misuse Risk but not proven causal risk factor	Organophosphate pesticidesRisk but not proven causal risk factor	Nutritional deficiencies eg zinc, magnesium, polyunsaturated fatty acids Correlate not yet proven risk factor	Family adversity & low income Correlate not yet proven risk factor
Maternal stress Risk but not proven causal risk factor	Polychlorinated biphenyls Risk but not proven causal risk factor	Nutritional surpluses eg sugar, artificial food colourings Correlate not yet proven risk factor	Conflict/parent–child hostility Correlate not yet proven risk factor
Low birth weight and prematurity Risk but not proven causal risk factor	Lead Risk but not proven causal risk factor	Low/high IgG foods Correlate not yet proven risk factor	Severe early deprivation Risk, likely causal risk factor