On average, if you're middle class, you'll have eight fewer years of healthy life than someone who’s rich. And even if you’re rich, you’ll have fewer healthy years than someone who is very rich.

The idea of a health gap isn’t revolutionary. But Sir Michael Marmot, President of the World Medical Association, says most of us believe it just affects the poor.

In fact - as Marmot argues in his new book, “The Health Gap” – there are big differences between the average healthy lifespans of all classes. Yes, a blue-collar worker will have a shorter life expectancy than her boss, but even a high level executive won’t be doing as well as the CEO.

Let’s come back to that blue-collar worker and her health gap. Poorer people tend to smoke, eat less healthy food, and experience crippling stress.

Relative poverty, even in childhood, has an effect on your neural pathways and even your chromosomes. “So stress,” Marmot explains, “can actually damage your physical health.”

“We need to think about stress in a different way,” Marmot says. “Stress does not equate with being busy. The key part of stress is lack of control.”

It’s that lack of control that holds the key to understanding how the health gap applies not just to the poor, but the middle class and even the rich.

Poverty doesn’t drive stress, but social stratification does.

If the top five percent of the population collects all the power, then everyone else’s sense of control – or lack thereof – will reflect in their stress levels, and eventually, their health.

That high-level executive? She might be doing well, but if her sense of power over her daily life is less than the CEO's, she'll still have a shorter life expectancy.

So how do you solve a problem like the health gap? Create conditions for people to have more control over their lives and reverse the trend of increasing social disadvantage.

As Marmot says, “It’s not just about trying to improve the health of those in poverty, but to improve the health of all of us.”