Left ventricular hypertrophy and left diastolic dysfunction are measures of structural and functional heart damage, which have been associated with an increased risk of cardiovascular-related death in adults. These cardiac measures are also used in the paediatric population as indicators of premature heart damage.

Arterial stiffness estimated from carotid-femoral pulse wave velocity has been discovered as a novel cause of increased blood pressure, insulin resistance, and metabolic syndrome in adolescents and young adults. It was also recently shown that increased blood pressure in adolescence may cause premature heart damage, but it is not known whether arterial stiffness could independently cause structural and functional damage to the heart.

The current study was conducted among 1,856 adolescents of whom 1,011 were female. The adolescents were 17 years old at baseline, and they were followed up for 7 years until young adulthood at age 24 years. Arterial stiffness, carotid intima-media thickness, and evidence of heart damage were assessed at baseline and follow-up. Signs of heart structure damage are left ventricular hypertrophy and high relative wall thickness, whereas signs of heart function damage are left ventricular diastolic dysfunction and increased left ventricular filling pressure.

During the 7-year follow-up period, the prevalence of heart structural damage among adolescents doubled. With extensive control for fat mass, muscle mass, glucose, insulin, blood pressure, lipids, smoking status, sedentary time, physical activity, socio-economic status, and family history of cardiovascular disease, and using adults’ cut points for diagnosing heart damage, it was observed that adolescents in the highest tertile category of arterial stiffness and carotid intima-media thickness had a 23 — 27% increased risk of progressively worsening structural heart damage.

Only arterial stiffness appears to independently cause both structural and functional heart damage, whereas increased carotid wall thickness does not seem to have a causal role. Increased carotid wall thickness is an early indicator of atherosclerosis, whereas increased arterial stiffness describes arteriosclerosis. The study further reported that arterial stiffness caused heart damage by increasing blood pressure and insulin resistance. The increase in blood pressure explained 34% of the heart damage caused by arterial stiffness. Moreover, insulin resistance explained 15% of the heart damage caused by arterial stiffness.

“We are seeing for the first time that arterial stiffness is a novel cause of several diseases such as hypertension, insulin resistance, metabolic syndrome, and heart damage in the young population. Among adults, arterial stiffness is currently being established as a cause of type 2 diabetes. We discovered that approximately 50% of the deleterious role of arterial stiffness in causing heart damage is enhanced by the mechanism of increased blood pressure and insulin resistance. Thus, preventing and lowering blood pressure and insulin resistance may potentially diminish the negative impact of arterial stiffness on the heart, by up to half,” says Andrew Agbaje, a physician and clinical epidemiologist at the University of Eastern Finland.

“Experimental and clinical intervention studies are urgently needed on comprehensive approaches to treating and reversing arterial stiffness from adolescence. At least, targeting blood pressure and insulin resistance leaves the problem half-solved,” Agbaje continues.

Dr Agbaje’s research group (urFIT-child) is supported by research grants from Jenny and Antti Wihuri Foundation, the Finnish Cultural Foundation Central Fund, the Finnish Cultural Foundation North Savo Regional Fund, the Orion Research Foundation, the Aarne Koskelo Foundation, the Antti and Tyyne Soininen Foundation, the Paulo Foundation, the Yrjö Jahnsson Foundation, the Paavo Nurmi Foundation, the Finnish Foundation for Cardiovascular Research, Ida Montin Foundation, Eino Räsänen Fund, Matti and Vappu Maukonen Fund, and the Foundation for Pediatric Research.

The team studied orangutans at a long-term monitoring site, Suaq Balimbing, in Sumatra. Orangutans at the site have been habituated over decades to the presence of humans, thus offering scientists a rare opportunity to observe wild great apes at close range. Caroline Schuppli, director of the Suaq Project and the study’s first author, became interested in how wild orangutans would react when presented with something unfamiliar.

“Curiosity is a trait that has driven the exceptional ability of humans to learn and innovate,” says Schuppli, a group leader at MPI-AB. “If we want to know how the trait evolved in us, we have to study it in our closest living relatives.”

Curiosity, which describes an individual’s motivation to learn about the unknown, has been studied before in great apes; however, due to the logistical difficulties of studying wild animals, almost all tests have occurred in captivity. “We know that apes are very curious to explore when they are in the safe and controlled conditions of a zoo,” says Schuppli. “But these results tell us little about what really triggered or suppressed curiosity over our evolutionary history.”

About ten years ago, Schuppli and collaborators first attempted to assess curiosity in wild orangutans with an experiment inspired by captive studies. They roamed Suaq, peppering the forest with foreign objects for the orangutans to find: a bright red flag; plastic flowers and fruits; a stuffed toy. The results were stark. “They hardly ever came near any of the items,” she remembers. “You could see them making huge circles in the forest to avoid the experiment.”

Schuppli realized that testing orangutans’ reaction to novelty in nature would require reimagining the past paradigm. “The challenge was figuring out how to entice them with something that was novel, but also familiar enough not to scare them off,” she says. Over the years Schuppli perfected just such an object: a piece of tree trunk with a natural hole filled with local forest honey. The tree hole and food were familiar, but deploying these in an unusual way represented a novel foraging situation. With a team of local and international scientists, Schuppli hoisted the experimental log into trees about 10 meters from orangutans — and watched what happened.

During the trials, the orangutans spent on average 30 minutes in the vicinity of the novel log. During this time, they explored the novel log by intensively observing it over extended periods of time and approaching it closely. Overall, however, orangutans rarely touched the branch directly; and when they did, they often used a tool, such as a stick to do so. “The orangutans were pretty cautious,” says Tri Rahmaeti, a team member from Universitas Nasional in Indonesia and co-author on the study. “The honey reward could have easily been scooped out of the log using a finger, but they still preferred to use a tool so they didn’t have to make physical contact.”

But there were significant differences in the behaviors. Using statistical techniques, the team uncovered traits of individuals and features in the environment that amplified exploration. Young orangutans were far more likely than adults to observe and approach. And, orangutans were more likely to approach the log if they saw another individual heading that way too. The habitat also seemed to play a role: in areas with abundant food, orangutans observed more but approached less.

Says Schuppli: “On the one hand, the results confirmed our hunch that orangutans in the wild are not that keen to explore new objects. This could be because in nature, orangutans live very long lives in stable habitats where novelty is rare. So, the potential risk of approaching something unknown doesn’t outweigh the potential reward.”

“On the other hand, the experiment showed that there is flexibility in the behavior. Orangutans have the potential to be curious about novelty in nature, but only under certain conditions. And by experimentally testing this in a wild population, we pinned down the conditions.”

Of these conditions, Schuppli finds the social factor most illuminating. “Orangutans are the least social of all great apes, and yet we find that the presence of association partners increases their curiosity,” she says.

This has fascinating implications for understanding learning and innovation — the products of curiosity that fueled the success of our species. “We often think of learning and innovation as solo acts, but this might not have been the case in our early history,” says Schuppli. “If novelty was the spark, then our social lives might have provided the accelerant.”