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A new target for deadly lead?

Thursday, April 9, 2009

Yesterday Janet Raloff of Science News wrote about a new study linking lead levels in older women to an increased risk of mortality. Naila Khalil and colleagues at the University of Pittsburgh report that women whose blood lead levels measure > 8 micrograms per deciliter were a whopping 60% more likely to die during the study. The main reason was heart disease and stroke. Since about 90% of accumulated lead is stored in our bones, elderly women are at increased risk because the loss of bone density releases lead into circulation in the bloodstream.

That's a lotta lead
Several things are notable about this study. For one, lead levels above 8 are these days high for adults - CDC studies indicate that fewer than 5% of American adults are estimated to have this much lead in their bodies. But a couple decades back, when lead was common in gasoline, these levels would have been pretty unremarkable. That means we are only learning decades later that this common and replaceable chemical was causing serious harm.

Hindsight is 20/20: What are we missing today?
If we miss dramatic things like chemicals that kill you, how can we be assured that other common chemicals like the ones contaminating your canned food, hair dye or shower curtain aren't also causing more subtle but insidious harms? We need a bit more respect for the fact that it is incredibly difficult to track down the environmental causes of common diseases, and try to prevent exposures instead of waiting three decades to study the results in affected adults.

Unique risks to older people
The second take-home lesson is the unique risks to an older population (and I don't just mean the elderly). We rightfully focus a lot of energy on preventing risks to children, whose immature body systems are incredibly vulnerable to environmental chemicals. But aging leads to increasing rates of chronic diseases, and a gradual decline in the body's capacities, especially to excrete toxic chemicals or repair the damages they cause. The persistent chemicals we've accumulated in our bodies reach their peak in later life. Common toxicants like lead and mercury strain the weakened cardiovascular system, and air pollution takes its toll on those with reduced lung capacity and lung disease.

Early exposures lead to problems later in life
Finally, in the case of BPA we've learned in the laboratory that early life exposures can alter organs in a way that only manifests later in life. Suk-Mei Ho and Gail Prins at the University of Cincinnati discovered that animals exposed to BPA in early life were more susceptible to prostate cancer when their body's hormone levels were changed to simulate the effects of aging. We need to take a closer look at the effects early life exposures that may not manifest for decades.

The good news: We've successfully reduced lead exposures
The good news here is that the substantial progress we've made to reduce lead levels in the environment will undoubtedly lower the lead-related mortality for future generations of women. However, we can definitely learn some humility from this example and apply what we've learned to our own daughters - even if we can't see the results today.

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