**10.8 Attention deficit hyperactivity disorder (ADHD)**

Attention deficit hyperactivity disorder is an early-onset, chronic, a neurodevelopmental disease characterized by attention deficit, hyperactivity, and impulsivity mostly in children, affecting nearly 2–18% of children worldwide, and is found to be one of the most common psychiatric disorders in childhood stage [32]. Learning like basic skills can be affected in childhood and can also cause various psychological and social interaction problems in children and the adult population. The neurotransmitters like dopamine (DA) and noradrenaline (NA) play a crucial role in maintaining attention, concentration, motivation, awareness, and cognition. With the major role of vitamin D in cerebral function, it might have a direct role

in the etiopathogenesis of ADHD in children and young adolescence. Further, vitamin D is also responsible for the regulatory synthesis of neurotrophic factors such as neurotrophin (NT), NT 3 and NT 4, nerve growth factor (NGF), and glial cell line-derived neurotrophic factor (GDNF), known to be significantly involved in cell differentiation and survival. Thus, ADHD is etiopathologically connected to vitamin D deficiency. In initial years of growth and development of life, vitamin D deficiency or extensive insufficiency can be harmful to neuronal development and function, resulting in stimulation of neurogenesis [7, 10].
