About two days into my trip to Vietnam I checked my steps on Fitbit - I know, I’m compulsive - and found something surprising. Or alarming. I wasn’t sure.

My resting heart rate had dropped. By about eight beats per minute. 

I know. I know. Nothing’s quite as boring as listening to someone yap about their stupid Fitbit data. But stay with me for a minute. There’s a point.

At first I thought it was a mistake. Or that I was in congestive heart failure. But nope, my heart rate dropped from an average of 64 beats per minute to 56 and stayed there for the entire trip.

Why, I wondered. 

After all, it was devilishly hot in Vietnam - surely that stresses the heart. I was walking even more than I do at home. On top of that, while in Hanoi I constantly risked death by crossing streets filled with rampaging motor scooters. That’s a jolt of adrenaline every few minutes.

So why was my heart rate dropping?

I found the answer in The New York Times. In an April 24 piece headlined, “Putting Down Your Phone Can Help You Live Longer,” the writer interviewed experts who claim that the constant use of smartphones produces the kind of stress that worsens all physical ailments. It has to do with the production of cortisol, the stress hormone.

“Your cortisol levels are elevated when your phone is in sight or nearby, or when you hear it or even think you hear it,” says David Greenfield, professor of clinical psychiatry at the University of Connecticut School of Medicine and founder of the Center for Internet and Technology Addiction. 
“It’s a stress response, and it feels unpleasant, and the body’s natural response is to want to check the phone to make the stress go away.”

“But while doing so might soothe you for a second, it probably will make things worse in the long run. Any time you check your phone, you’re likely to find something else stressful waiting for you, leading to another spike in cortisol and another craving to check your phone to make your anxiety go away. This cycle, when continuously reinforced, leads to chronically elevated cortisol levels.

And chronically elevated cortisol levels have been tied to an increased risk of serious health problems, including depression, obesity, metabolic syndrome, Type 2 diabetes, fertility issues, high blood pressure, heart attack, dementia and stroke.

“Every chronic disease we know of is exacerbated by stress,” says Dr. Robert Lustig, emeritus professor in pediatric endocrinology at the University of California, San Francisco, and author of “The Hacking of the American Mind.” “And our phones are absolutely contributing to this.”

I live on my smartphone. Like a lot of you, I start by checking emails and from there I head down the Twitter rabbit hole. Hours can pass with my neck holding steady at a 45-degree angle.

My phone is my constant companion. I sleep with it on the nightstand so I can roll over and check my messages first thing in the morning and take a final look at the screen before I go to sleep. Shoot, I need a bedside phone in case a big news story breaks 3 a.m. Wouldn’t want to wait till 7 to learn about it.

My phone is perpetually vibrating, ringing and chiming. New text messages, new emails, new Facebook posts, new Tweets. A lost dog in my neighborhood. A new cat video. A change in the stock market.

Nothing gets by me. Thanks to my iPhone.

Like a lot of digital mouth-breathers, I instinctively pull out my phone if I’m in line at the supermarket or in a doctor’s waiting room. I even grab my phone and start scrolling when I’m stopped at a red light.

But when I arrived in Vietnam I put the phone on silent, stuck it in my pocket and rarely looked at it. I wasn’t able to receive text messages or make phone calls, and I was too busy to spend much time on social media.

My cellphone became nothing more than a camera and I was able to focus on where I was, without endless distractions.

It was relaxing.

But as soon as our plane pulled up to the gate at Dulles, my phone was lit. Minutes later I was texting, Tweeting, sparring with political opponents and answering emails.

My first day home, Friday, my heart rate was up to 58. Saturday, 60. Sunday, 62. 

Boring fitness data, I know. Sorry.

On Sunday night I read the New York Times piece and wondered if there could be a connection.

So I tried an experiment: On Monday I left my phone at home when I ran errands. Yep, I actually ventured out of the house without my digital life jacket. Next, I left my phone on my desk in my study overnight.

My heart rate dropped to 60.

Coincidence? Nope, cortisol.