Australasian Science Magazine

By Tim Olds

The release of stress hormones may have helped our ancient ancestors to survive dangerous situations, but modern stresses are killing us slowly. How do you rate on a common stress scale?

He ate a Palaeo (strictly speaking a Neo) diet, and even at the age of 45 spent his days trekking across the Italian Alps. He was very lean – he had a Body Mass Index of 18.5, right at the bottom of the healthy range. A typical meal was venison, unleavened herb bread and fruit.

But for all these healthy lifestyle habits, Ötzi the Iceman, the 5300-year-old Austrian (or is it Italian?) glacier mummy, was a cardiovascular minefield with calcification in several major arteries.

Ötzi is not alone. Around the world there are enough atherosclerotic mummies to fill a museum. A study of 137 young adult mummies dating back 3500 years from Egypt, Peru, the US and the Arctic found evidence of arterial hardening in 34% of them (http://tinyurl.com/a5z4uln), about the same prevalence that we see today. And this despite their Peruvian diets of beans and yams, or their Aleutian hunter-gatherer lifestyles devoid of sugar.

Why do humans have such a predisposition for cardiovascular and other lifestyle diseases? One conceptual framework that is gaining currency is the allostatic load model. Allostatic load is the sum of stresses to which we are subjected over the course of a lifetime. The stresses may be physical, such as injuries and infections, or psychosocial, such as divorce or exams. Stress leads to the release of neuro-endocrine hormones such as epinephrine and cortisol, which have physiological “fight or flight” effects that are adaptive in the short-term but maladaptive when they become chronic.

Epinephrine, for example, will increase the amount of blood your heart pumps out, and increase blood pressure, carrying more oxygen to the muscles. In the short term this allows us to have more energy delivered to the muscles for immediate action, but high blood pressure leads to arterial stiffening in the long term.

Cortisol causes an immediate release of blood sugar, providing instant energy, but chronically high levels of blood glucose will lead to excessive production of insulin, insulin resistance and diabetes.

These responses appear to be an evolutionary trade-off: short-term gain for long-term pain. It’s easy to understand why this would be an adaptive trade-off when humans endured nasty, mean, brutish and short lives. You’re not too worried about getting diabetes when you’re 50 if there’s a cave bear chasing you! When you’re up to your arse in alligators, as they say, you’re not thinking about draining the swamp. In fact, you probably wouldn’t live to 50 anyway, so your fight or flight genes are likely to be passed on before they have noticeable effects.

The allostatic load model proposes that modern lifestyles are particularly stressful. We are much more likely to encounter strangers today than when we lived in isolated groups of 100 or so people. There are the everyday stresses of noise, traffic and deadlines. There are novel and challenging work situations. And because we live long enough for the effects to translate into disease, we see high levels of lifestyle diseases.

There are ways of quantifying allostatic load, some relying on biochemical analyses, others on simple questionnaires. The commonly used Holmes and Rahe Stress Scale is commonly used rates life events on a score out of 100 for stressfulness. A score of 300 points or more is bad news. At the top of the list for adults is the death of a spouse (100 points) and divorce (73). Divorce is a bit worse than mere separation (65).

Good events are also stressful, so marital reconciliation adds another 45 points. The separation-reconciliation combination (110 points) can be a real killer. Even Christmas gets you 12 points, so it’s better to get the marital issues over and done with early in the year.

For kids, the death of a parent and unplanned pregnancy are top of the list (100 points), while being suspended from school (50) is not quite as bad as getting a fail grade (56).

The extent to which stressful events, both physical and psychosocial, trigger a stress response, and the degree to which that stress response becomes chronic and translates into physiological problems, depends on events early in life (often while still in the womb), genetics and health behaviours. Some nutrients, such as omega 3, may modulate certain aspects of the stress response, such as inflammation. Each bout of exercise induces an acute stress, but repeated physical activity reduces levels of epinephrine and cortisol. Adequate sleep reduces stress, as do various meditation techniques.

Allostatic load is a powerful tool to explain why we get lifestyle diseases, why some people are more susceptible than others, and why lifestyle habits can exacerbate or mitigate them.

It turns out that the Iceman had a strong genetic predisposition for cardiovascular disease, so all his lifestyle habits did him no good. Or maybe the daily stress load was just too great. Ötzi had an arrowhead embedded in his shoulder and at least three bouts of serious illness in the 6 months before his demise. I’m not sure how many stress points that would score, but I bet it would be pretty high.

Professor Tim Olds leads the Health and Use of Time Group at the Sansom Institute for Health Research, University of South Australia.