By the time you finish this article, your brain will have changed. Something you read or something that happens while you’re trying to focus on these words will go on to have an impact on your day.

If that event happens to be stressful – maybe you are interrupted by loud colleagues or a loved one calls with bad news – it can trigger a series of more stressful events such as choosing something unhealthy to eat or being unintentionally rude to a friend or co-worker.

That chain reaction, if repeated, takes a toll on your overall health and wellness. Stress has been shown to be an aggravating factor in, among other conditions, heart disease, diabetes and mental health problems. That might explain why US life expectancy has fallen three years in a row.

At least that’s the theory of Sanjay Gupta, one of the best-known doctors in the US, who has made stress the centerpiece of his documentary One Nation Under Stress.

“Stress still remains one of those terms people throw around and maybe not everyone is meaning the same thing when they use the word stress,” Gupta told the Guardian. “I think the idea of being busy is not fairly equated with stress – the idea of not having control, not having predictability of sense, not feeling that you have some autonomy in your life is a much bigger stressor than I realized.”

In the documentary, which premieres on HBO, Gupta speaks with scientists, affected individuals and his own family to figure out how a country that spends $3.5tn a year on healthcare could see life expectancy shrink three years in a row. The documentary runs just over an hour – but packs in dozens of interviews to present a comprehensive picture of stress in the US.

“The only population of people in the developed world whose life expectancy continues to go down, mortality rates go up, is the white working class in the United States,” said Gupta, a practicing neurosurgeon and CNN’s chief medical correspondent. “And the unifying factor was this toxic level of stress.”

Gupta explores these numbers, which have puzzled doctors, with the Princeton economists Angus Deaton and Anne Case, who in November 2015 published a groundbreaking study that showed a sudden surge in death rates among white, middle-aged Americans since 1999.

Coverage of this study has raised questions about how seriously the nation has taken the life expectancy of minority communities who have historically borne the brunt of health disparities.

But Gupta turns out to be a fitting guide for negotiating this conflict as the son of Indian immigrants who grew up alongside white working-class people in a small Michigan town.

Gupta explains how the white people he grew up with were the children of the “greatest generation” and raised with optimistic predictions about what their future held. “Their sons and daughters were supposed to inherit the earth and that didn’t happen,” Gupta said.

“It’s this idea that dashed expectations – having expected to receive something and not receiving it – is particularly toxic when it comes to creating a level of relentless stress,” Gupta said. “It’s almost an existential stress; it’s about your identity.”

To zone in on this, Gupta meets with his mother and a white childhood friend, Frankie Sgambati Jr, to discuss life in Michigan in the 1970s and 1980s. Though much attention is paid to the struggles of the white working class in the documentary through wrenching personal interviews, Gupta’s own stories about wanting to change his name to Steve to fit in and about how being the only brown child in town when the Iran hostage crisis was happening was “brutal”, add another layer.

Meanwhile, in Gupta’s current hometown of Atlanta, health outcomes change by zip code – creating lasting disparities in care for the black population compared with the white population.

Charles Moore and Dr Sanjay Gupta in One Nation Under Stress. Photograph: HBO

Charles Moore, chief of head and neck surgery at Grady Health System in Atlanta, has tried to shrink the gaps in health access by offering care to the impoverished on a sliding-fee scale at the clinic he founded, HEALing Community Center.

“For African Americans it’s been a chronic state of stress,” Moore said in the documentary. “For certain white populations it’s a new issue and possibly that’s what’s crossing that decline for them. The white working class have not seen that systemic oppression.”

Gupta and director-producers Marc Levin and Daphne Pinkerson first set out to make the documentary after the Centers for Disease Control reported in 2015 that life expectancy in the US dropped for the first time since 1993. That downward trend continued as the documentary developed.

Levin and Pinkerson’s most recent documentaries for HBO have focused on how global economic forces shape people’s lives, but health was never a central piece of the stories they told.

“It was a refreshing way to see where we are at,” Levin said. “We may be wealthy as a nation, but we’re not healthy.”

Levin said he was initially dismissive of the idea that stress could be such a prominent driver of health outcomes, but as they worked on the film, more and more scientific evidence about the impact stress has on health became available.

When asked how close the US is to addressing the factors that have allowed this declining life expectancy, Gupta laughed and Levin replied: “I would say: [not] how close – how far?”