Study in Ecuador finds a common health-risk measure may not be universal
EUGENE, Ore. — (May 30, 2012) — New findings from Ecuador suggest a key measure used to gauge a person's risk of cardiovascular and some other diseases in advanced countries like the United States may not work in less-developed countries. At play is exposure to microbes.
For the study, researchers from Northwestern University in Evanston, Ill., and the University of Oregon collected finger-prick blood samples from 52 adults, ages 18 to 49, each week for a month to measure the levels of C-reactive protein (CRP).
About one third of U.S. adults have chronically elevated CRP. Acute elevations in CRP — a protein in the blood whose levels rise as part of the inflammatory response — help protect people against infectious disease, but chronically produced levels of CRP are associated with chronic diseases.
This study — done in lowland Ecuador where the UO has led the Shuar Health and Life History Project since 2005 — found no evidence of chronic low-grade inflammation. The seven-member team's findings appear in a paper placed online ahead of regular publication in the American Journal of Human Biology.
The researchers found the Shuar people experienced high levels of CRP during infections from normal exposure to local microbes but levels fell quickly to low, non-chronic levels upon recovery.
"In other words, CRP goes up when you need it, but it is almost undetectable when you don't, after the infection resolves," said lead author Thomas W. McDade, professor of anthropology at Northwestern and faculty fellow at the university's Institute for Policy Research. "This is a pretty remarkable finding, and very different from prior research in the U.S., where lots of people tend to have chronically elevated CRP, probably putting them at higher risk for chronic disease."
McDade said the findings build on his previous research in the Philippines, which found that higher levels of microbial exposure in infancy were associated with lower CRP as an adult. Similar exposures during infancy in lowland Ecuador, where rates of infectious disease continue to be high, may have a lasting effect on the pattern of inflammation in adulthood.
"In my mind the study underscores the value of an ecological approach to research on the immune system, and it may have significant implications for our understanding of the links between inflammation and chronic disease," McDade said. "This may be particularly important since nearly three-quarters of all deaths due to cardiovascular disease globally now occur in low- and middle-income nations like the Philippines and Ecuador."
It may be, he said, that levels of chronic inflammation seen in the U.S. are not universal and may be a product of a population-level disease transition that has lowered people's exposure to infectious microbes. Infectious microbes have been part of the human ecology for millennia, and it is only recently that more hygienic environments in affluent industrialized settings have substantially reduced the level and diversity of exposure.
UO researchers — led by Lawrence S. Sugiyama and J. Josh Snodgrass, co-directors of the Shuar Health and Life History Project — have been gathering CRP data from both Shuar and nearby non-Shuar settlers. Sugiyama has been working with the nation's Jivaroan speaking people since 1993. Data collected for this study, led by McDade, were analyzed at his Northwestern lab.
"For this study, we collected data in three different communities over three months — two months with the team, then a month of finishing up — but establishing the field site with Shuar Federation collaboration required a couple years and then ongoing yearly work," Sugiyama said. "Until this study, we had not collected the repeated measures needed to determine whether Shuar suffer chronic high levels of inflammation, or whether inflammation dropped after acute infection. That is what one would predict should be the evolved mechanism, because inflammation is costly in various ways."
The new study also served to build on previous doctoral research by recent Aaron Blackwell, who graduated in 2009 from the UO and joins the faculty at the University of California, Santa Barbara, this fall. "Aaron was looking at tradeoffs between growth and immune function among Shuar," said Snodgrass. "His intriguing results demonstrated that the timing and intensity of early exposure to pathogens tracks people into different immune and growth profiles — and this has relevance for the development of disease later through inflammatory and other pathways."
A primary goal of the UO's Shuar project is to integrate and facilitate research with colleagues, by maintaining a long-term field site and engaging in collaborative research, which have or now include scientists from UCSB, Harvard, Northwestern, Yale and the University of California, Los Angeles. "Some of our other work, for instance, focuses on cross-cultural testing of psychological hypotheses about cognitive adaptations for social exchange, generosity, foraging and attractiveness," Sugiyama said.
Tara Cepon, a UO doctoral student and co-author on the new paper, currently is studying the Shuar's exposure to parasites, including worms, and how that may later increase the risks of developing allergies and autoimmune diseases.
"The field sites in Ecuador show a lot of variability in lifestyle within the same culture, which allows us to look at the effects of differences in exposure to infectious disease and variation in diet," Snodgrass said. "We're really excited about the potential of Cepon's research." That work is being done in collaboration with UO biologist Brendan Bohannan, whose lab is performing DNA sequencing on gut microbes that are obtained.
"This collaborative research represents an example of the University of Oregon's global reach and impact," said Kimberly Andrews Espy, vice president for research and innovation. "It also demonstrates the benefit of careful, long-term observation in a specific ecological and cultural context that is emblematic of the type of high-quality, interdisciplinary research conducted at the university. The findings have broad implications for how we frame health care policies and practices around the world."
Co-authors on the new paper with McDade, Sugiyama, Snodgrass and Cepon were: Paula S. Tallman of Northwestern University, former UO doctoral student Felicia C. Madimenos and current UO doctoral student Melissa A. Liebert. Sugiyama is also affiliated with the Center for Evolutionary Psychology at UCSB.
The National Institutes of Health (grant 5DP10D000516), National Science Foundation (BCS-1027687), Louis S. B. Leakey Foundation and Wenner-Gren Foundation (7970) supported the research.
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