How stress ages both monkeys and humans

The writer is a science commentator

The slings and arrows of climate misfortune appear to leave their imprint on the immune system. A colony of monkeys that survived Hurricane Maria, which devastated Puerto Rico in 2017, show signs of accelerated ageing, according to a recent study. The finding adds to a growing body of research suggesting that stress and trauma of any kind, including that caused by extreme weather, may cut lives short.

More than 1,000 rhesus macaque monkeys roam the islet of Cayo Santiago, off the coast of Puerto Rico. The animals, descendants of primates shipped from India in 1938, have the run of the place which is off-limits to humans except researchers. Managed primarily by the University of Puerto Rico, they have blood samples drawn regularly.

Researchers were able to compare samples taken before and after the hurricane. Of particular interest was the pattern of gene expression in immune cells: this alters with age, and is linked to the onset of age-related diseases such as Alzheimer’s. Inflammation genes show increasing activation, for example. The hurricane-hit animals showed, on average, typical patterns of pre-storm ones that were two years older.

The storm, in other words, seemed to “age” survivors by two years, equivalent to about seven to eight human years. The study, led by Marina Watowich at the University of Washington, found that some monkeys aged faster than others: the scientists now plan to examine whether social bonds influenced immune resilience.

Professor Janet Lord, from the Institute of Inflammation and Aging at the University of Birmingham, says it is reasonable to infer that extreme weather might adversely affect people too. “We know physical and emotional stress ages people, not just immunologically but biologically as a whole.”

The study of how stress affects aging, health and lifespan is a relatively new field but emerging evidence, Lord says, seems consistent. People who suffer very stressful events, such as traffic accidents or terrorist attacks, may have shorter lives and succumb relatively early to age-related diseases. Lord has studied older adults who suffer hip fractures: six months after the injury, she says, many show measurable aging of their immune systems.

There are two key drivers at play: inflammation and stress hormones. Injury triggers inflammation, a known factor in aging, that can persist for a long time. Psychological trauma can cause stress hormones such as cortisol to be raised for extended periods, another characteristic linked to aging.

Older patients are harder hit in both scenarios: first, they tend to suffer more inflammation after injury than younger ones; second, they are less able to produce counter-stress hormones, primarily DHEA (dehydroepiandrosterone), to balance out the cortisol. “We carry on making cortisol but make less DHEA from about the age of 30,” Lord explains. “That’s why we get less good at dealing with stress as we get older.”

Just as women undergo the menopause, all humans experience this “adrenopause”. And just as hormone replacement therapy can fix the shortfall in estrogen, Lord plans to test whether giving DHEA supplements to older people after major injury can stem stress-related decline. A preliminary dosing study is under way.

The main message is that stress is bad for human health, particularly for those no longer in resilient youth. Societies should be actively trying to reduce stress levels, Lord thinks, not just by doing their best to prevent severe crises such as hurricanes and wars but also by addressing the everyday anxieties felt by those in deprived circumstances.

As healthy life expectancy between rich and poor areas in England can differ by nearly 19 years, truly leveling up on health will mean dialing down the stress felt by those at the bottom.

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