Lead and Hypertension in Adults
Air Date: Week of April 26, 1996
While many studies have been conducted on the effects of lead exposure in children, Doctor Howard Hu shares findings from a recent study on how exposure to lead manifests as high blood pressure in a number of adults. Steve Curwood speaks with Dr. Hu, the lead author of the recent study cited in the Journal of the American Medical Association.
CURWOOD: It's Living on Earth. I'm Steve Curwood. Today, nearly 1 in 4 Americans has high blood pressure, or hypertension. Elevated blood pressure can lead to heart attacks and strokes, but in most cases doctors say they don't know why people get it. There are some well-known links. Being overweight, smoking cigarettes, and failing to get exercise are some. And now, some researchers at the Harvard School of Public Health have come up with another one: low level exposure to lead. Even small amounts of lead have been shown to cause neurological disorders in children, but the Harvard group is the first to look at how low doses might affect adults. Their study of 500 men, just published in the Journal of the American Medical Association, found a strong link between lead and hypertension. Dr. Howard Hu was the lead author.
HU: If you compare the men with the lowest fifth of lead in their bone to the men with the highest fifth of lead in their bones, the risk goes up 50%.
CURWOOD: Now when you say the top fifth, are you talking about the top fifth of the United States, are you talking about everybody, or just your study?
HU: Well, these were men who had the usual garden variety exposures to lead that all of us had in the 1960s and 1970s. The fact that they had very few high untoward or occupational exposures to lead makes me conclude that this is representative of middle aged to elderly men throughout the entire country.
CURWOOD: At what levels are people showing hypertension? What are the lead levels that cause problems?
HU: Our study did not show a specific level above which there's a risk and below which there is no risk. Rather, the increasing amount of levels of lead that show up in your bones confers incremental increases in risk for hypertension.
CURWOOD: So it's fairly parallel, if you --
HU: That's right --
CURWOOD: -- have 50% more lead than somebody else, you might have a 50% more chance of hypertension.
HU: That's correct.
CURWOOD: Why do you think there's a link between lead and hypertension?
HU: Well, lead is an omnipotent toxin. It really affects enzyme systems that are critical to the function of many organs throughout the body. But we think that the main target organs, in terms of hypertension, are the kidney and perhaps the direct, the vascular system itself. You know, in our companion piece in the Journal of the American Medical Association, we show that very low levels of lead lead to kidney impairment. So, since the kidney is a critical organ for the control of blood pressure, you put these 2 articles together and it suggests that low levels of lead affect the kidney, and that kidney damage leads to hypertension.
CURWOOD: What about race and ethnicity in this? Blacks seem to have a much higher hypertension rate than the white population. Is there any link here to lead, do you think?
HU: That's another interesting question that we'd like to investigate. Blacks not only have much higher risk of hypertension, but they also have, on average, higher exposures to lead if you look at blood lead levels. Well, you put those 2 facts together and it makes you wonder whether blacks are inordinately susceptible to hypertension because of their exposure to lead.
CURWOOD: What do you think should be the safe levels of exposure to lead, based on your studies?
HU: Well, based on these studies, I think we should seriously think about lowering the acceptable amount of lead exposure in adults towards what it is for children. We measure lead exposure by using blood lead levels, which is adequate, because blood lead levels reflect your ongoing exposure, and the current standard for children is 10 micrograms per deciliter. We don't allow children to have levels above that. Right now the level that's acceptable for adults is 40, and perhaps we should lower it to 10.
CURWOOD: What's to be done? If someone has lead in their body, they have hypertension, what tests should they have? And if they have this stuff, how can they get it out of their body, or can they?
HU: Well, it's premature to conclude that lead induced hypertension can not only be identified in individuals but also treated. That's research that needs to be done, now that studies like our own have found this relationship.
CURWOOD: But wait a second. You're saying that 20% of adult men can blame some of their hypertension on lead, but you say you haven't proved this?
HU: No, what I'm saying is that this effect, which I do believe is probably a causal effect, may not be reversible. If it is reversible, then it opens up an interesting possibility that we can treat hypertension by neutralizing lead burden in a definitive way. You know, most Americans when they develop hypertension have to take drugs for life. If this is a cause of hypertension that's treatable, perhaps we can treat it and cure it.
CURWOOD: Dr. Howard Hu is an epidemiologist at the Harvard School of Public Health. He recently published two studies in the Journal of the American Medical Association, one linking bone lead levels to impaired kidney functioning, the other linking it to hypertension. Thank you.
HU: Thanks for inviting me.
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