There is no safe level of lead exposure for children; lead affects intelligence even at very low levels.
- The rate of IQ loss per 1 micrograms of lead per deciliter of blood (ug/dL or 10 parts per billion) is greatest at lead levels below 10 ug/dL (100 ppb).
- As a child’s blood lead level (BLL) increases from 1 to 10 ug/dL (10-100 ppb), experts estimate a child may lose anywhere from 3.9 to 7.4 IQ points.
- Low-level chronic exposure may have an even greater effect on IQ than a single instance of very high BLL. 
New studies and re-interpretation of past studies demonstrates that it is not possible to determine a threshold below which BLL is not inversely related to IQ. 
Elevated BLLs are associated with Attention Deficit Hyperactivity Disorder (ADHD) and antisocial behavior, which in turn increase the likelihood of conduct disorder.
The Center for Disease Control and Prevention (CDC) has gradually lowered the blood lead level of concern (the BLL where intervention is recommended) from 60 ug/dL (600 ppb) in 1960 to 10 ug/dL (100 ppb) in 1991.
- Most recently, in January 2012, the Advisory Committee on Childhood Lead Poisoning Prevention (ACCLPP) recommended dropping the term “level of concern” entirely and using a “reference value” to provide a way to compare an individual child’s blood lead level to a population of children the same age.
- An accumulation of evidence showing negative health effects at very low levels of exposure supported this change. The current reference value is 5 ug/dL (50 ppb) and will shift with population blood lead levels.
Certain vitamins and minerals, especially calcium, iron and vitamin C, play a specific role in minimizing lead absorption. It is reasonably well-established that iron deficiency is associated with increased BLLs, and that some effects, such as lower IQ, can result from both conditions.
 Low Level Lead Exposure Harms Children: A Renewed Call for Primary Prevention, Report of the Advisory Committee on Childhood Lead Poisoning Prevention of the Centers for Disease Control and Prevention dated January 4, 2012
 Issue Brief: Childhood Lead Exposure and Educational Outcomes by the National Center for Healthy Housing