Lead, smoking and the cause of ADHD
Recently, there have been a number of news articles about how lead and smoking during pregnancy may lead to ADHD. Here is one such article. While these findings are important, I want to put them into context.
The causes of ADHD have been studied extensively. While there is always room for further understanding and research, we have great knowledge now. An excellent new book on the causes of ADHD was recently published, and is the most comprehensive review of the research to date. It is called: What causes ADHD? Understanding What Goes Wrong and Why By Dr. Nigg
The facts are that about 80% of the cause of ADHD is genetic, and 20% is acquired.
Genetic ADHD
Research has shown that ADHD clearly runs in families. Twin studies, family studies and now genetic research have clearly demonstrated the genetic link of ADHD. Geneticists have identified approximately 5 ‘candidate genes’ which can be an issue in ADHD.
When looking at the ‘heritability’ of a disorder, researchers look at what percentage of the cause of a disorder is due to genetics.
Here is a comparison of heritability of different medical conditions:
The heritability of breast cancer: 30%
The heritability of asthma: 40%
The heritability of height: 85%
The hertitability of ADHD: 80%
So, ADHD clearly runs in families, and genetics account for about 80% of the known cause.
What accounts for the other 20%?
Acquired Causes of ADHD
After we account for the genetic causes of ADHD, there are several acquired causes.
The acquired causes can be broken down into Prenatal (i.e. before birth), and Postnatal (after birth).
Prenatal Causes of ADHD:
Prenatal causes of ADHD include the events that happen while the mother is pregnant. They include:
- Maternal smoking during pregnancy (2.5 x risk)
- Maternal drinking alcohol during pregnancy (same risk)
- Prematurity of birth (especially if brain bleeds - 45% have ADHD)
- Overall increase in pregnancy complications
Postnatal causes of ADHD:
Postnatal causes of ADHD are the events that occur after birth. They include:
- Head injury
- Brain hypoxia (i.e. lowered oxygen to the brain)
- Brain tumor
- Brain infection
- Lead poisoning in preschool years (0-3 yrs old)
- Survival from Acute Lymphoblastic Leukemia (’ALL’ - the treatments cause ADHD)
Where does the quoted study fall into this information?
As is always the case in science, new studies help to replicate old findings, and carry the information forward. This study reiterates the risks of smoking and lead exposure, and moves our understanding forward in this regard.
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Written by Dr. Kenny Handelman - The ADHD Doctor
To find get a FREE special report on ADD/ADHD Medication, visit: Medication Mastery
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Email this post to a friend:
September 24th, 2006 at 10:40 pm
Dr. Handleman,
My son has suffered from asthma, chronic ear infections and drug allergies since he was an infant. I have often wondered if any of these conditions or medications given for these conditions has ever been linked to adhd?
Thanks.
Cathy M.
September 24th, 2006 at 11:53 pm
Hi Cathy.
Excellent question.
Regarding asthma, ear infections, and drug allergies - there are no scientific data showing that these conditions are a cause of ADHD.
As I describe above, 80% of the cause is genetic, then 20% is acquired - with some pre-birth and some causes post birth. These disorders and their treatments do not cause or contribute to ADHD.
Kenny Handelman, MD
July 1st, 2008 at 2:59 am
I don’t know about all the meds and stuff; I got my diagnosis as an adult (just last year, in fact), so no one knew what was wrong with me as a kid, just that something was and it was somehow my own doing. ADD really does exist, but not everyone needs to take meds for it (heck, I’m one of several ADDers I know who don’t take meds). I don’t and I’d like to keep it that way.
July 6th, 2008 at 6:46 am
I have ADD and i have taken adderall and ritalin. I am happy to say that i am now doing “OK” without any medications, which is great because i always was very frusterated with my life. My fiancee’s brother was on straterra, among others, and he ended up commiting suicide. It is horrible to think that so many people are being put on these dangerous drugs at ages i can’t comprehend. Kids 3 and 4 years old are being damaged by these medications, and I just don’t understand the point.