Lead poisoning

is much better than it used to be, but still a problem. Our Grand Rounds (the old fashioned kind, not the new-fangled one) this morning was a case of lead poisoning, and an article out in this weeks JAMA (subscribers only, I believe)is getting publicity.

Encouragingly, the percentage of kids with lead levels >10 mcg/dl, the current cut off for it being too high has fallen from 88% of the population to <5%. Mostly from outlawing leaded gasoline and paint.

While the cut off for what is acceptable has steadily come down from 60 in the 1960s to 10 today, it may still be too high. A recent study suggested each 1mcg/dl increase in blood lead was associated with a 1.37 point drop in IQ. They tried to control for other factors like socioeconomic status and maternal IQ, so it is not just that stupid parents have stupid kids and live in old, dilapidated houses. Based on that, the difference between a lead level of 0 and 1 of 10 would be about 14 IQ points or 1 full standard deviation. That is a lot. Interestingly, the incremental difference in IQ declines as lead levels rise

One caution is that in the IQ study, the population was none-too-bright to start with an average IQ of around 90 and an average maternal IQ of just over 80. Studies with premature infants have shown that being premature and poor stimulation (like you might expect if your mom had an IQ of 80) act synergistically to lower IQ and delay development. The system is resilient to insults, but once the insults add up, you get into trouble. I wonder if a similar situation could be at play here. That the combination of lead and poor social environement is negatively synergisitc.

Anyway, if you believe the IQ data, kids should be much smarter than they were in the past: 15 or more points on average. That seems a bit unlikely, but maybe they'll be a lot more physicists soon. On the other hand, the kids in this study were almost 10 IQ points smarter than their mom's, which could be lead.

The new study in JAMA this week shows that follow up of kids with high lead levels is poor. Almost 1/2 of kids with blood lead levels >10 are never retested. Part of the problem is they don't follow up, but almost 60% get some medical care in the next 6 months, so that isn't the only reason.

Treatment is not great. Education about avoiding lead exposure is obvious. Remediation to remove lead from the home is effective, but expensive and landlords have a lot more political pull than poor families, so, as a society, we haven't been willing to pay for it. For very high levels you can give agents that chelate (basically bind up) the lead.