According to a study published in the December issue of Paediatrics, prenatal exposure to tobacco smoke, including lead during childhood has been directly linked to an increased risk of attention deficit hyperactivity disorder (ADHD) in children.

For the study, researchers analyzed data collected from a representative sample of U. S. children aged 8 to 15-years during the 2001-2004 National Health and Nutrition Examination Survey on prenatal tobacco and childhood lead exposure.

The researchers calculated prenatal tobacco exposure by reported cigarette use during pregnancy, and measuring childhood exposure to lead by assessing blood levels. According to them, youngsters with prenatal exposure to tobacco smoke seemed 2.4-times more likely to have an increased likelihood of ADHD, as did those with blood levels in the top third of the population
(2.3-times).

In combination, researchers said, the effects of both toxicants were even greater, with children having an eight-fold increased chance of being diagnosed with ADHD when exposed to both, compared to others without exposure to either.

The authors of the study contend theirs is the first to provide the first estimate of joint effects of the two common toxicants. Data on 2,588-youngsters from the National Health and Nutrition Examination Survey (2001-2004) was examined with 8.7% meeting criteria for diagnosis with ADHD. ‘Our findings suggest that reduction of toxicant exposures may be an important avenue for ADHD prevention and they underscore the enormous burden that may be associated with continued exposure to tobacco and lead,'’ the researchers conclude.

Levels of 10-micrograms per deciliter are considered ‘actionable’ by the U. S. Centres for Disease Control and Prevention (CDC), while for the study children in the upper third had blood lead levels of 1.3-micrograms per decilitre or greater; those in the middle group had levels between 0.9 and 1.3-micrograms per decilitre.

Previous research has also indicated an association between lead toxic for children’s brains and lower IQs and hyperactivity in children, with Dr. Andrew Adesman, Chief of Developmental and Behavioural Paediatrics at Schneider Children’s Hospital in New Hyde Park, N. Y. saying: ‘There is no such thing as a ‘safe’ level of lead.’

Further, according to Dr. Adesman: ‘we have long believed ADHD is at least in large part due to abnormalities of dopamine in the brain,’ with previous research showing exposure to lead and cigarette smoking alters the brain’s metabolism of dopamine.

The CDC reports there are 250,000 children aged 1 to 5 in the USA, who have blood lead levels greater than 10-micrograms of lead per decilitre of blood. And, even though there has been a drop in blood lead levels in recent years, there are children who are still exposed to lead from peeling paint, particularly those who reside in poor, inner-city neighbourhoods in old buildings. In 1978, the US government banned leaded paint for most residential usage.

Lead can also be ingested by children from old water pipes, the soil and lead-based toys, with major toy manufacturers like Mattel and Fisher-Price issuing multiple recalls in the past few years of products manufactured in China, containing unsafe levels of lead.

With so much lead out there, it is important to take precautions by keeping children away from peeling paint, including making it a practice for children to wash their hands thoroughly after playing in soil.

Good nutrition, ensuring children get adequate levels of iron and calcium, also offers protection against exposure to lead, as it has been found that iron and calcium deficient children absorb more lead than children on better diets.