Life expectancy in the United States ticked upward between 2000 and 2015, but that rise was blunted by increasing rates of opioid-related deaths, a new report finds.

Overall, life expectancy at birth increased by 2 years between 2000 and 2015, the report found. The life expectancy for a person born in the U.S. in 2000 is 76.8 years, compared with 78.8 years for a person born in the U.S. in 2015.

Much of this increase in life expectancy can be attributed to a decrease in death rates from the leading causes of death in the country, including heart disease, cancer and stroke, according to the report, which was published today (Sept. 19) in the journal JAMA. Lower rates of death from these causes and several others contributed to a increase in life expectancy of more than 2 years, the researchers found. [America's Opioid-Use Epidemic: 5 Startling Facts]

But increasing death rates from other causes cut into this gain in life expectancy, according to the report. These causes included Alzheimer's disease, suicide, chronic liver disease, septicemia (a blood infection) and, most notably, unintentional injuries — a category that includes drug overdoses.

Drug-overdose deaths increased from about 17,400 deaths in 2000 to about 52,400 deaths in 2015, the researchers said, and the majority of these deaths were due to opioids. Drug-overdose deaths contributed to a decrease in life expectancy of 0.28 years, with opioid-related deaths accounting for 0.21 years of life expectancy lost, according to the report.

In fact, the loss of life expectancy from drug overdoses was as big as the loss of life expectancy from Alzheimer's disease, suicide, chronic liver disease and septicemia combined, according to the report. The reason the overall loss of life expectancy isn't larger, however, is that death rates from other types of unintentional deaths, such as car accidents, decreased over the course of the study period.

In addition, the researchers noted that the change in life expectancy due to opioid-overdose deaths is "likely an underestimate." This is because up to 25 percent of death certificates for drug-related deaths don't mention a specific drug, according to the report.

Between 2000 and 2014, the annual average increase in U.S. life expectancy has been 0.15 years, which is less than the annual average increase in life expectancy of 0.2 years that was recorded between 1970 and 2000, according to the report. And from 2014 to 2015, life expectancy in the U.S. decreased, the researchers said. Currently, life expectancy in the U.S. is lower than life expectancy in most other high-income countries, but preventing opioid-related deaths could help achieve larger increases in life expectancy once again, the researchers said.

To calculate life expectancy, the researchers used data from the National Vital Statistics System Mortality file, a database that contains death certificates from all 50 states and the District of Columbia.

Originally published on Live Science.