Suicide rates among young people are rising, reaching the highest levels since 2000, a study published Tuesday finds.

But most alarming, the researchers said, was a 21 percent rise in boys aged 15-19 dying by suicide in 2017 from the year before.

"Previous studies talked more of an increase in female suicide, but what we’re showing is that rates among males are also increasing rapidly," Oren Miron, the study's lead author and a research associate in biomedical informatics at Harvard Medical School, told NBC News.

As part of the study, published in the Journal of the American Medical Association, Miron and his colleagues analyzed data on suicides from 2000 to 2017 from the Centers for Disease Control and Prevention. They focused on teens and young adults between 15 and 24.

They found that in 2017, the suicide rates for this age group reached their highest levels since 2000. That includes an increase of 8 percent among girls aged 15-19 dying by suicide from 2016 to 2017, according to the new research.

Experts not involved with the study, however, caution the new data may not reflect an overall trend.

"The question that we can't answer about 2017 is, is this the beginning of a greater increase in youth suicide deaths or an anomaly in an otherwise steady trendline?" said Jonathan Singer, president of the American Association of Suicidology, a nonprofit that advocates for suicide prevention. "We will have to wait until 2019 data are available to have any way of answering that question."

Still, there is no doubt that over time, a steadily growing number of young people are dying by suicide.

"I think what you’re seeing is a reflection of an incredibly stressed out group of kids," Singer said.

Warning signs can be vague

The warning signs of depression and possible suicide ideation can be vague, especially during the teenage years, when it's often perfectly normal to go through phases of moodiness and withdrawal. And experts in the field say serious mental health problems can manifest themselves differently from person to person: anger in one person, chronic headaches in another, excessive crying in others.

"One of the best things to do is make sure that kids are surrounded by adults who can monitor them, who know them, both online and offline, and who are thinking, 'How do I know when this kid is doing well, and how do I recognize signs of distress?'" Singer said.

"You don't see if you're not looking for it."

"You don't see it if you're not looking for it," said Fenway Jones, 16, of Fenton, Mich.

One of Jones's closest friends, a boy named Jasper, died by suicide in 2017, the year the new data show an uptick among teen boys. Jasper was 16 years old. The two friends had bonded over their shared love of the game Dungeons and Dragons.

"It was super shocking and devastating," Jones told NBC News. "I had seen him just a little while before he died." She said didn't notice anything that would have given her a clue her friend was suffering.

"We weren’t looking for the minor changes. We saw the happiness that he had, and we didn't see the other side of it."

Within the year, another one of Jones's friends, a 16-year-old girl named Tori, also died by suicide.

Jones, then just 14, used her grief to start a group called Jasper's Game Day. She and others travel to gaming conventions to spread awareness about suicide, and to reduce the stigma surrounding mental illness.

"I tell them it's OK to not feel OK," Jones said.

When two of her friends died by suicide, Fenway Jones, 16, started a group called Jasper's Game Day to raise awareness about mental health. Courtesy of Fenway Jones

Her efforts appear to be working. Since Jasper's Game Day began two years ago, thousands of people have approached Jones to talk about mental health.

"They tell me their personal stories: how they dealt with depression, struggles or even if they attempted suicide or knew someone who did," Jones said.

Money raised by Jasper's Game Day through sales of T-shirts and bracelets is donated to local crisis centers.

Something going on on a societal level

The new study found that in 2017, 6,241 teenagers and adults in their early 20s died by suicide. Young men accounted for the vast majority — 5,016 — of those deaths.

Potential explanations for the apparent increased rates shown among teen boys during that year are unclear. Indeed, other studies find that suicide rates in teen and young adult women are increasing.

One possible explanation is that "boys, as a rule, are a little more impulsive than females," said Dr. Greg Plemmons, a pediatrician and researcher at Vanderbilt University in Nashville who was not involved with the new study. "But girls are catching up."

Plemmons led a study last year that found the rate of hospitalizations for suicidal thoughts or attempts increased for both boys and girls over the past decade. The research team identified 115,856 emergency department visits from 2008 to 2015 for suicide ideation or attempts in young people.

However, they saw "a bigger jump among adolescent females compared to males," Plemmons said.

"Something is going on on a societal level," he said. "We certainly need more intervention."

If you or someone you know is in crisis, call the National Suicide Prevention Lifeline at 800-273-8255, text HOME to 741741 or visit SpeakingOfSuicide.com/resources for additional resources.

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