(CNN) - The suicide rate in the United States continues to climb, with a rate in 2017 that was 33% higher than in 1999, new research finds.
Suicide rates among people 15 to 64 increased significantly during that period, rising from 10.5 per 100,000 people in 1999 to 14 per 100,000 in 2017, the most recent year with available data, according to annual research published by the US Centers for Disease Control and Prevention's National Center for Health Statistics on Thursday.
The report noted that America's suicide rates are at the highest level since World War II. Those who identify as American Indian or Alaska Natives had the highest increase among all race and ethnicity groups, according to the research.
The research included data on deaths in the United States from the National Vital Statistics System's multiple cause of death files for 1999 and 2017.
The data showed that suicide deaths among girls and women rose significantly for all racial and ethnic groups except Asian or Pacific Islander, and the largest increase was among American Indian or Alaska Native girls and women, at 139%.
Among boys and men, suicide rates increased significantly for all racial and ethnic groups except for Asian or Pacific Islander, with the largest increase observed among American Indian or Alaska Native boys and men, at 71%.
The research had some limitations, including that deaths can be misclassified and that deaths among American Indian, Alaska Native, Asian, Pacific Islander and Hispanic people may be misclassified to other race and ethnicity groups.
Overall, American Indian or Alaska Native teens and adults 15 to 44 had the highest suicide rates for both males and females in 2017, the research found.
A CDC report published last year found that suicide rates increased 25% across the United States between 1999 and 2016, with individual states ranging from a 6% increase in Delaware to a nearly 58% increase in North Dakota.
Suicide rates rising for young people
The latest findings also fall in line with a separate study, published in the medical journal JAMA on Tuesday, that found a significant increase in suicide rates among 15- to 24-year-olds between 2000 and 2017.
That study found that among those 15 to 19, the suicide rate was 8 per 100,000 people in 2000 and increased to 11.8 per 100,000 in 2017, and among young adults 20 to 24, the suicide rate was 12.5 per 100,000 people in 2000 and then rose to 17 per 100,000 in 2017.
For some health experts, the rise in suicide comes as no surprise.
Although previous research highlighted a dramatic surge in suicide rates among young people, "this is unfortunately not a surprise," said Nadine Kaslow, a professor of psychiatry and behavioral sciences at the Emory University School of Medicine and chief psychologist at the Grady Health System in Atlanta, who was not involved in the new paper.
Other studies have found increases in suicide rates, especially among adolescents and young adults, but the previous research "adds a couple of points; one is noting this particular increase in young males and also in this younger age group of 15 to 19," Kaslow said on Tuesday.
She added that identifying why there has been an increase remains a topic of interest among experts.
To get help, call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255). There is also a crisis text line. For crisis support in Spanish, call 1-888-628-9454.
The-CNN-Wire ™ & © 2019 Cable News Network, Inc., a Time Warner Company. All rights reserved.