How environmental factors may raise ADHD risk

Read about the latest studies on attention deficit hyperactivity disorder (ADHD).

27 July 2015
by Karen Nel

The myriad causes of attention deficit hyperactivity disorder (ADHD) continue to puzzle the medical community. While a strong genetic link has been established, environmental factors also undoubtedly play a role. Here are three of the newest studies into possible environmental causes of ADHD.

1. Use of household pesticides may increase prevalence of ADHD

A recent study published online in the journal Environmental Health has found a link between exposure to household pesticides and ADHD, particularly in boys. The study, published in May 2015, focused on exposure to pyrethroid pesticides and the prevalence of ADHD, especially with regard to symptoms such as hyperactivity and impulsivity.

Pyrethroid pesticides are widely used in household and agricultural pesticides. They were developed as a less toxic alternative to organophosphate pesticides, which were banned for home use in the early 2000s.

Study leader Dr Tanya Froehlich, a paediatrician at Cincinnati Children's Hospital in the US, and her research team analysed data from nearly 700 children aged eight to 15. The researchers examined levels of 3-PBA – a chemical indicator of exposure to pyrethroids – in the children's urine. Boys with detectable levels of 3-PBA in their urine were three times more likely to have ADHD than those without detectable 3-PBA. “Given the growing use of pyrethroid pesticides and the perception that they may represent a safe alternative, our findings may be of considerable public health importance,” reported Dr Froelich.

See here for more on this study.

2. Factors during pregnancy and delivery may predict later risk of ADHD

A study published in the January 2014 issue of Pediatrics, the official journal of the American Academy of Pediatrics, identified a number of pregnancy- and delivery-related risk factors for the later development of ADHD in children. The study, led by Desiree Silva, a professor of paediatric medicine at the University of Western Australia, analysed 12 991 children and adolescents with ADHD and 30 071 children without the disorder, who acted as a control group. 

Smoking during pregnancy, maternal urinary tract infections during pregnancy, being induced, and experiencing threatened preterm labour were all found to increase the risk of the subsequent diagnosis of ADHD in both boys and girls.

However, oxytocin augmentation of labour appeared to offer some form of protection against the development of ADHD in girls. The authors cautioned, however, that the oxytocin correlation may have been a “chance finding”.

See here for more on this study.

3. ADHD could be linked to altitude

Findings published in March 2015 in the Journal of Attention Disorders, suggest a relationship between rates of ADHD in the US population and the average altitude of US states. Led by Rebekah Huber of the University of Utah, the researchers found that ADHD rates decreased by 0.001 percent for each 1 foot (30.48cm) increase in a state’s average altitude.

ADHD is associated with unusually low levels of the neurotransmitter dopamine. Dopamine works as a chemical signal in the brain to indicate the presence of oxygen. Because oxygen is rarer at higher altitudes, the researchers suggest that higher levels of dopamine production in areas of high elevation may help protect children against developing ADHD.

It is also possible, the researchers say, that regional differences in ADHD rates are actually driven by the intensity of sunlight hitting the higher elevated states. Previous research has suggested that sun exposure could regulate disruptions to the internal clocks that set our sleep schedules. These sleep disruptions have also been associated with the development of ADHD.

See here for more on this study.

IMAGE CREDIT: 123rf.com