ebook_ADHD2019

The World Federation of ADHD Guide 9 prematurity and low birth-weight are the most studied. A recent meta-analysis of the literature on the association between both very-premature and/or very low- -weight babies and ADHD showed a 3 times increased risk for those infants to have ADHD in the future. 13 However, it is important to note that prematurity and low-birth weight are risk factors to other mental disorders. Anyhow, whenever assessing very premature and/or very low birth weight children, clinicians might consider assessing for ADHD. Maternal smoking during pregnancy has been widely studied as a risk factor for ADHD. It is well documented that smoking during pregnancy places the fetus at risk for birth complications, including low birth weight, which has been asso- ciated with ADHD. Maternal smoking also places the fetus at risk for a hypoxia, which has been associated with ADHD. Although Langley et al.’s 14 meta-analysis concluded that children whose mothers’ smoked during pregnancy had a 2.4 fold increased risk for ADHD, this is still an area of debate because ADHD and its polygenic risk are known to be associate with smoking behaviors. Thus, mother with ADHD might smoke more than mothers without ADHD and the risk is asso- ciated to genetic factors related to ADHD and not to smoking. Those who favor the maternal smoking hypothesis point out that it is a plausible risk factor because nicotine regulates the activity of the dopamine transporter, the site of action of the stimulant drugs that treat ADHD. People who experience mild traumatic brain injuries (mTBIs) are at risk for developing ADHD. This was the conclusion of a meta-analysis which showed that mTBI associated with ADHD. 15 Another well-documented environmental risk factor is severe institutional deprivation in early childhood. We know this from studies of children who spent the early years of life in Romanian orphanages that offered poor nutrition and nearly no human contact. Many of these children deve- loped ADHD later in life. 16 Environmental risk factors for ADHD that have been confirmed by meta-a- nalyses include: yy preterm birth, 17 yy prenatal exposure to maternal smoking, 18 yy prenatal methylmercury exposure from maternal fish consumption, 19 yy exposure to lead, 20 and yy perinatal vitamin D deficiency. 21 From meta-analyses, we can also exclude some environmental factors as incre- asing the risk for ADHD. These include: sugar consumption, 22 methylmercury in vaccines, 19 maternal thyroid hormone insufficiency, 23 sleep restriction, 24 cesarean section 25 and solar intensity. 26 It is easy to see how toxic exposures, pregnancy and delivery complications, traumatic brain injuries and severe institutional deprivation could affect the deve-