Age Doesn't Mean Heart Disease For Bolivian Tribe
IRA FLATOW, host:
You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow.
For the rest of the hour, what a tribe in the Amazon region of Bolivia can tell us about our own health. Researchers have been studying the Tsimane tribe, who still live a relatively traditional life in the Amazon rainforest, the kind of thing you might think about, you know?
They're hunters, they're gatherers, they're physically fit, they have a low diet in fat. But with all this healthy living, there's something really interesting going on there.
They also have risk factors for heart disease that we folks in Western modern cultures have. They have high levels of CRP, you know, that protein. They have signs of inflammation in their arteries, but they don't have the heart disease that are associated with these risk factors.
Why is that? Well, here to explain the mystery, maybe translate some of it for us, certainly better than I did, is Eileen Crimmins. She's professor of gerontology at the University of Southern California. She joins us by phone.
Welcome to SCIENCE FRIDAY, Dr. Crimmins.
Dr. EILEEN CRIMMINS (University of Southern California): Glad to be here, Ira.
FLATOW: Tell us a little bit about that tribe.
Dr. CRIMMINS: Well, this is a tribe that you don't find very often in the world anymore. They have a very short life expectancy, only about 42 years. They have very high levels of infection, and they live an isolated life.
They have very little contact with modern medicine, modern society. They don't read and write. We were interested in them because we are interested in how people age and we want to understand a little bit better how we evolved and how the way we age might be linked to the world that we've lived in in the past. So we see this group as really representing a world that is similar to the one that the rest of the world used to live in, but doesn't anymore.
FLATOW: But you found in looking at their blood chemistry and their arteries representatives of the risks that we live in today.
Dr. CRIMMINS: Well, we found one of the risks.
Dr. CRIMMINS: They have very high C-reactive protein, and that's a recently recognized risk factor for heart disease and…
Dr. CRIMMINS: …countries like the United States, once you account for cholesterol and hypertension, C-reactive protein becomes another factor similar to those that is indicative of your risk for heart attack and stroke and mortality and the bad things that happen to people as they age. In this population, they live with very high C-reactive protein all their lives because they have very high levels of infection. But they don't appear to have the vascular damage that we have in the United States and other countries like the United States.
We are not saying that this is somehow an ideal world, because obviously people die very young, but they don't die with diabetes. They don't die with overweight. They don't die with - they have very little hypertension. They have very low cholesterol. So they look quite different from the rest of us in terms of the way they age.
FLATOW: So CRP, high levels of that is an indication of inflammation, is it not?
Dr. CRIMMINS: It is an indication of information. And they probably have high levels of - and they have high levels of inflammation, and it's related to the fact that they have constant infectious diseases.
If we have high levels of inflammation in this country, it could be related to the fact that we are obese or that we have perhaps recently had an injury like a heart attack or we've had a surgery or something like that for different reasons. We can even have high levels of CRP in over the short term for just things like having infectious disease, but then it goes down.
But over time, people with C-reactive protein gets higher with age in this country, the United States.
FLATOW: Would it - yeah. Would it - might signify that we're looking at the wrong thing, our society looking for CRP levels as (unintelligible) indicator?
Dr. CRIMMINS: I don't know if it's looking at the wrong thing. I think it's a risk factor, but it's one that interacts with the rest of the world that you live in. And if you don't have high cholesterol and you have a lot of physical exercise, then it might not mean the same thing as it does in a society like this.
We were looking for damage to your arteries that would be - that would come from having this constantly high circulating level of C-reactive protein, and we're not seeing that.
It doesn't mean that your heart isn't being damaged in other ways if you live in a very, very infectious world.
FLATOW: I see. Is CRP a result of damage to artery or does it cause…
Dr. CRIMMINS: It's both.
FLATOW: It's both.
Dr. CRIMMINS: That's one of the issues. It's a complicated thing. And we're just starting to disentangle that, even in countries like the United States, what's cause and what's effect. And as usual, it seems like causation goes in both ways. So it's both a cause of having a heart attack but once you have a heart attack it goes way up, very, very quickly so…
Prof. CRIMMINS: …it's one of those things that seems to be part of the body that's constantly reacting to the physiology of what's going on. And it's acting and reacting.
FLATOW: Well, I'm going to bring up the nature, nurture question.
Prof. CRIMMINS: Yeah.
FLATOW: Yeah. You knew I would.
Prof. CRIMMINS: Well, that's what it is.
(Soundbite of laughter)
FLATOW: I mean could there - there must - since we're all made of genes and they're made of genes, I mean, should there be not be some genetic reason for this? For them being - high CRP, but yet their arteries are perfectly healthy?
Prof. CRIMMINS: We could have different genetic - we could have a different distributions of some genes or alleles in our population and in this population. We basically know that as for these tribes in South America you get a real range of distributions of genes that we know about. We don't know about this tribe in particular. It's something we're working on. It could be genetic. It could be people's reaction to disease is somewhat different but we think probably that's not a big part of the explanation, could be a part of it, however.
FLATOW: Hmm - 1-800-989-8255, we're talking about some interesting work with Eileen Crimmins, professor of Gerontology at UC - University of Southern California. What about older people? You said most of these people died in their 40s.
Prof. CRIMMINS: Well, that's what I said the life expectancy was. Most of these people actually are at risk of dying when they're babies but once you make it through being a baby and you become an adult then this group has a very high mortality up to the age of 60.
Prof. CRIMMINS: So people, once they become adults, tend to die in their 60s and 70s. They still die younger than in the United States but when you have a life expectancy of 40 what it really means is that you have a very low, a much lower probability of getting to be an adult.
FLATOW: So - and the folks who did die in their 60s that you studied…
Prof. CRIMMINS: They're gone.
(Soundbite of laughter)
FLATOW: But they didn't have heart disease even then.
Prof. CRIMMINS: Oh, we don't see the evidence that they have had heart disease. Now, there are more things to look at. We think that potentially this group that has lead a very, very infected life may have more damage to their heart valves and the organs that we have not been able to pick up yet. We are investigating that. This is a group that my colleagues, the anthropologists, go visit in a very remote area. They live two days, you know, it's an hour by plane from the capital city, two days by truck, and two days by canoe.
They have no electricity. They've done a remarkable job collecting these samples and measuring what we've measured so far, and now they're trying to bring sonograms in and get measurements of their actual condition of their heart valves.
FLATOW: I mean, you must be, you know, like from another planet coming in there with this medical equipment.
Prof. CRIMMINS: Somewhat.
(Soundbite of laughter)
Prof. CRIMMINS: You're skipping a few centuries of knowledge…
FLATOW: And they're not, they're not fearful of allowing you to poke them and prod them and things like that?
Prof. CRIMMINS: It's a very - it's a very carefully organized situation, the tribal leaders are involved. The tribal leaders have agreed to it. We have a lot of protection of people who are in the studies. And you ask, why might they participate? Well, they participate because they actually do receive exams from a doctor and that's who collects the information and the doctors actually sometimes can do something to help you. And in particular what they actually have been able to do relatively easily is save people's babies from dying.
So, while we're really interested in studying aging, there are some fairly basic technological things you can do just to feed and hydrate babies when they're dying. And actually the life expectancy has gone up nine years while - just in the few short years this team has been in there researching this tribe. So the reason they want to be researched is they want the health care.
FLATOW: But you're not, but you're not, you know, I'm thinking of quantum mechanics here. You're not influencing the experiment by going in there…
Prof. CRIMMINS: That's true.
FLATOW: …aren't you.
Prof. CRIMMINS: But that's real life - that's life with people.
FLATOW: Yeah, you're not worried about affecting the outcome of what you're going to find?
Prof. CRIMMINS: No we are. I mean, we'd love to leave people pristine so we could be able to study them but it's not ethical. We - if you are in there as a doctor examining somebody and you see something that you can easily do something about, you have to do it.
Prof. CRIMMINS: And so that's, you know, we're not there basically to provide - providing medical care is not what we're doing as an aim but it's a side effect of being there.
FLATOW: Let me get a question or two in here. George(ph) in Oakland. Hi, welcome to SCIENCE FRIDAY.
GEORGE (Caller): Hi.
FLATOW: Hi, there.
GEORGE: So how these keep from infecting or exposing these people to infectious diseases that the experimenters might carry when you go to visit them?
FLATOW: Good question.
Prof. CRIMMINS: Well, there's relatively small team that goes in and the team that goes is native Bolivians and members of the Tsimane tribe who serve as translators and with a small number of anthropologists from the United States. Now - and anthropologists from Bolivia. These people have typically been in the city in Bolivia before they go out to the country for a week or so. So if they have some specific illness it would be picked up. They're careful about it, they try to monitor it. But…
Prof. CRIMMINS: …you know, and to date, we haven't had a problem.
FLATOW: So where do we go from here?
Prof. CRIMMINS: Well, what we're interested in is basically understanding what goes on in this tribe, to understand what went on in human societies over a long period of time. So we feel that the big issue is we evolved in a world that we don't live in now.
Prof. CRIMMINS: We evolved in a world that was infectious, that had scarce resources and where people had to do hard work to actually achieve the resources they needed to live. And that all of a sudden, within 100 years, the world changes and people's physiology may not be well adapted to the world we live in now. So that's really the basic question we're trying to get at is, how does infection and the sources of energy and the supply of energy and the expenditure of energy interrelate to actually affect people today in countries like this and other countries?
So for instance, we're all experiencing an obesity epidemic. Why is that? Is it because we're somehow just don't have the willpower? Or we - is their some real almost evolutionary push to eat what's on the table?
(Soundbite of laughter)
Prof. CRIMMINS: And…
FLATOW: And maybe they can answer that…
Prof. CRIMMINS: …well they may help.
FLATOW: Yeah, all right. Dr. Crimmins, thank you for taking time to be with us. And good luck to you.
Prof. CRIMMINS: You're welcome. Bye, bye.
FLATOW: Goodbye. We were talking with Dr. Eileen Crimmins, who is professor of gerontology at the University of Southern California, who is down visiting the Tsimane tribe in the Amazon rainforest.