Noel Mueller, PhD, an assistant professor with the Johns Hopkins Bloomberg School of Public Health, studied the blood pressure of the Yanomami and Yekwana tribes in Venezuela. (Kim Hairston, Baltimore Sun video)
Bananas are so crucial to the diet of the Yekwana people of Venezuela that they honor esteemed guests like Noel Mueller by inviting them to stay in the hut where the fruits are stored.
That diet — and the health of the Yekwana and a neighboring tribe, the Yanomami — may also be factors in explaining why blood pressure rises with age among Americans and other peoples of developed nations, according to research done by the Baltimore epidemiologist.
Mueller, an assistant professor at the Johns Hopkins Bloomberg School of Public Health, visited the tribes in their remote homeland in the Amazonian rain forest two years ago in order to test a long-held dogma of cardiology: that blood pressure rises steadily across the human lifespan as a consequence of aging.
Mueller has long been skeptical of that conventional wisdom, in part because most research supporting the idea has been conducted by Western scientists on Western subjects.
Gathering data among the two Amerindian tribes, he and an international research team found that blood pressure did not rise at all across the lifespans of Yanomami individuals, who have almost no exposure to Western influences.
In other words, where blood pressure does increase with age, it does so commensurately with exposure to the salt-heavy diet Westerners favor — and that suggests we can take measures to prevent the rise.
“If age doesn’t cause a rise in blood pressure, that suggests that the rise in blood pressure with age is due to lifestyle components, and those can be largely modified,” Mueller said. “It may not be true for all cardiovascular risk factors, but the fact that it’s true for blood pressure is pretty astounding and important. It’s something we can really do something about.”
The findings were published in an article in last month’s issue of JAMA Cardiology.
High blood pressure, also known as hypertension, affects more than a billion people worldwide, most of them in developing countries, according to a 20-year joint study by the World Bank and the World Health Organization published in 2010. About 75 million Americans are affected.
The study, titled the Global Burden of Disease, found that high blood pressure — which is associated with increased risk of heart disease, stroke and kidney failure — is the single largest contributing factor to disability and death in the world.
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“High blood pressure is a very common thing, and it’s becoming more common around the world every year,” Mueller said. “If we know it’s caused by lifestyle components, not aging, we know it’s something we can really do something about.”
A Wisconsin native who earned his bachelor’s, master’s and Ph.D. degrees at the University of Minnesota, Mueller, 34, has long been interested less in how to cure existing diseases than in preventing their development in the first place.
That interest — and fluency in Spanish, a skill he developed while living in South America — led him to Hopkins, where he joined the faculty in 2015 and enjoys joint appointments in the Department of Epidemiology and at the Welch Center for Prevention, Epidemiology and Clinical Research.
He has also long been intrigued by the results of INTERSALT, a study of hypertension conducted around the world during the 1980s.
That study found that the Yanomami — a tribe of about 35,000 hunter-gatherer-gardeners who live in a remote region of southern Venezuela and northern Brazil — had the lowest average blood-pressure measurements of all the people studied.
Among the most isolated people on earth from Western life, the Yanomami live on a high-fiber diet featuring lots of fresh fruits and vegetables, including bananas, plantains and casaba melons, and proteins such as the meat from capybaras. Members of the tribe have an average daily salt intake of about 1 gram — about one-tenth that of Americans.
A smaller nearby tribe, the Yekwana, meanwhile, registered blood pressure slightly higher than the Yanomamis.
Numbering about 6,600 people, the Yekwana are an isolated tribe as well, and have a similarly high-fiber diet. But an airstrip for small-engine planes in their midst offers them greater access to a few Western goods, including salt and a range of processed foods and condiments.
With the help of microbiologist Maria Gloria Dominguez-Bello of Rutgers University, a Venezuelan citizen, and Dr. Oscar-Noya Alarcon, a parasitologist with the Amazonic Center for Research and Control of Tropical Diseases in Venezuela, Mueller’s team secured the necessary governmental permissions to focus more intently on the health of the two tribes than INTERSALT did.
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The team flew into the jungle, landing on the Yekwanas’ airstrip, and stayed with them during a 10-day expedition, living on the tribe’s traditional diet and making frequent excursions to visit the Yanomami.
The researchers laid the foundation for a cross-sectional study — a statistical snapshot of a population at a given point in time — by measuring the blood pressure of 72 Yanomami and 83 Yekwana people between ages 1 and 60.
The mean increase in blood pressure from one year to the next was markedly higher in the more Westernized Yekwana than in the Yanomami, and the differences were apparent in both of the most commonly used forms of blood-pressure measurement.
The Yekwanas’ systolic blood pressure, which is measured in the arteries when the heart muscle is contracting, rose by 0.25 millimeters of mercury (mm Hg) per year; their diastolic blood pressure (taken between heartbeats) rose by 0.18 mm Hg annually. The Yanomamis’ never rose at all.
The study also showed that the difference in blood pressure measurements between the tribes began before age 20, suggesting that blood-pressure differences may emerge in childhood.
Among other observations, the team noticed that members of the Yekwana made liberal use of salt and ketchup on their foods when it was delivered by plane — and took to wearing T-shirts with Western logos — whereas the Yanomami, who lived a day’s travel away by canoe, showed no such influences.
Finding remedies lies outside the scope of the study, but heavy salt intake is known to be linked to high blood pressure.
Mueller’s team could firm up their results by studying the Yekwana and the Yanomami over a course of years, but the increasing volatility of Venezuelan politics — and the difficulty of securing funding for research projects outside the United States — could complicate the goal.
That would be unfortunate for Mueller the sightseer, who said the team was fortunate enough to travel by helicopter over such jaw-dropping scenery as Angel Falls, the highest waterfall on earth, and the flat-topped tepui mountains.
He also loved the hospitality of the Yekwana, a people whose leaders were kind enough to allow him to stay in the hut in which they store their fruit.
The arrangement did cause an awkward moment when the epidemiologist woke up one night to find a tarantula near his hammock and bats flying around his head — a situation that left him reaching for a machete in panic.
But he still believes that reaching across cultures can bring a lot of insight, scientific and otherwise.
“It’s important to understand the underlying causes of high blood pressure in isolated populations,” Mueller said. “And the people there were so sweet and welcoming. They wanted to leave the best impression of their tribes. I wish more of my research could include the Yekwana and the Yanomami.”