Lead and attention deficit hyperactivity disorder

Environmental lead remains an important public health concern worldwide despite successful reductions in its presence in recent decades. Attention deficit hyperactivity disorder (ADHD) is a common, impairing, and poorly understood condition with associated cognitive and emotional features, occurring in about 3%-6% of children worldwide. Although ADHD is influenced by genetic liability, it also has environmental influences that likely emerge via genotype by environment interplay and may involve epigenetic effects, although this remains controversial. Lead is among these known influences. This association holds even at the relatively lower exposure levels now common in developed countries, clarifying why reduced lead levels have not correlated with reduced incidence of ADHD. Recent studies suggest effect is causal and not an artifact of unmeasured confounds.