I timed the interview all wrong. At 9.27am, three minutes before I’m supposed to call him, I’m running down the street in the rain. I duck into the nearest cafe, and it has too many people, but it’s 9.29 so I call him anyway. I’m standing in the garden now, yelling over the rain and the speaker blasting shitty jazz, trying to hear Dr Kevin Chapman, a specialist in anxiety disorders and adults and adolescents.

Like so much language about mental health, the term “anxiety” has seeped into everyday conversation in a way that has made its meaning go flabby. “Worrying about your family, your health, the health of significant others, punctuality, your performance at school, at work, small repairs … these are things we all think about,” Dr Chapman says. “But what makes generalized anxiety disorder (GAD) different is that these worries are like a light switch. People with GAD have a hard time turning off the switch, even when things are going well.”

Put very simply, GAD is chronic worry.

In the US, the typical age that GAD appears is 31. And the likelihood of experiencing an anxiety disorder rises then declines. But we only have data on three broad age groups; people between 26 and 49 are 44% more likely to have experienced GAD in the past year compared with those who are younger, and 70% more likely than those who are older. (These are findings from the 2008–2012 Mental Health Surveillance Study by the Substance Abuse and Mental Health Services Administration).

In Scotland, the prevalence of GAD is broken down into smaller age groups (shown in the illustration here). But the data also has its flaws – it comes from patients who have gone to speak to general practitioners about their symptoms at least once in a 12-month period. There are no doubt others who experience GAD but have not spoken to a doctor about it. In Canada, the data is broken down into even smaller age groups, but the numbers refer to mood and anxiety disorders.

Despite this, the US, Scotland and Canada show a similar pattern when it comes to GAD. Women are more likely than men to experience anxiety. Also, our 30s and 40s are an anxious period of our lives. Are these patterns a consequences of our genes or the world around us?

To explain, Dr Chapman first clarifies another term that has become diluted in our language: neuroticism. “What neuroticism really refers to is a genetic predisposition to experience emotions frequently and intensely.” If you have neuroticism and an environment that is triggering your tendency to worry, then you’re much more likely to experience GAD.

As a woman in my 30s, I think about how triggering my environment feels as Dr Chapman lists off some examples of anxious thoughts: “What if my mother dies unexpectedly?” (Check.) “What if I run out of money to pay for my rent?” (Check.)

“Emerging adults are exceptionally more anxious today than they used to be,” Chapman says. (The term “emerging adults” makes me think of a rabbit cautiously peering out from a warren, but it actually just means people in their 20s and early 30s). “You have what I call a higher IOU – a higher intolerance of uncertainty.” I instantly feel a little defensive, and ask whether it’s our tolerance that has changed or whether our lives are simply more uncertain now.

Chapman agrees, but he says we have a tendency to view uncertainty and ambiguity as threatening, when in reality, they aren’t. He gives the example of a small, everyday exchange between friends. You text your friend to say: “Hey, wanna hang out later today?” And your friend replies: “Sure.” People who have a propensity for anxiety will assume that “sure” means that their friend might be upset with them.

If this all sounds familiar, it might be worth looking for the resources offered by the Anxiety and Depression Association of America, the association that put me in touch with Dr Chapman. I don’t have time to find out more, though. I have another meeting in 15 minutes in a building 25 minutes from here.