(Reuters Health) - Mortality rates for infants, children, and young adults have fallen in the U.S., Canada, England and Wales, but death rates in a new study were still higher for American youth than for young people in other countries.

Previous research has found babies more likely to die in the U.S. than in other developed and affluent nations, but the current study suggests this is true even later in childhood and early adulthood.

“The rates for major causes of death among infants, children and young adults generally declined over the study period; this is great news,” said senior author Meredith Shiels of the National Cancer Institute in Bethesda, Maryland.

“Unfortunately, the U.S. still lags behind Canada and the United Kingdom in terms of overall mortality rates for children, and, within the U.S., death rates remain higher among American Indian/Alaska Natives and black children, compared to other racial/ethnic groups,” Shiels said by email.

Overall, from 1999 to 2015, mortality rates for people under 25 years old declined 0.82 percent per year to 4.01 percent a year, researchers report in JAMA Pediatrics. But the U.S. had higher mortality rates for all age groups than Canada or England and Wales.

In the U.S., black babies had the highest infant mortality rates, at 1,128 per 100,000, followed by 968 per 100,000 for American Indian/Alaskan Natives.

By contrast, infant mortality rates were 498 per 100,000 white babies and 466 per 100,000 Latino babies in the U.S.

In all other age groups in the U.S, American Indian/Alaska Natives had the highest mortality rates.

Deaths from sudden infant death syndrome (SIDS) declined in the U.S., but mortality rates rose for suffocation and strangulation in bed, the analysis found.

“Among infants, declines in SIDS-related deaths have been attributed to public health efforts focused on promoting placing babies on their backs while sleeping,” Shiels said. “The increase in unintentional suffocation and strangulation in bed as cause of death may be due to reclassification of deaths that would have been classified as SIDS-related in an earlier time period.”

Accidental deaths also became less common in the U.S during the study period, largely due to declines in deaths from motor vehicle crashes, Shiels said.

Deaths from suicide and drug overdoses increased, however.

This is “consistent with what has widely been reported in the adult population,” Shiels said. “Increases in drug overdose deaths have been attributed to an increase in the number of people abusing opioids, as well as an increase in the risk of death due to heroin and fentanyl.”

The study wasn’t a controlled experiment designed to prove whether or how specific changes in medicine or shifts in behavior at the population level might directly impact mortality rates for young people.

“The increase in unintentional drug poisoning is undoubtedly related to the ongoing opioid epidemic,” said Evan Peet, an economist at the RAND Corporation in Pittsburgh, Pennsylvania, who wasn’t involved in the study.

“Mental health issues underpin youth opioid abuse and the increase in suicides reported in this study,” Peet said by email.

Disparities in mortality rates may begin in infancy in the U.S., at least in part because black families are more likely to have parents and caregivers share beds with babies, increasing the risk of SIDS, said Dr. Anna Pease, a researcher at the University of Bristol in the U.K. who wasn’t involved in the study.

“We’ve known for some time that the infant mortality rates in the U.S. were higher than in other countries, but this paper adds to our understanding about some of the causes of death and how these vary across different ethnic groups,” Pease said by email. “In a country with wide social and economic inequalities between white, black and native populations, it’s not surprising that death rates differ, but this paper shows that for infant deaths, this inequality gap is getting wider and this is bad news.”

SOURCE: bit.ly/2QpDOOw JAMA Pediatrics, online October 1, 2018.