Americans born in 2017 are expected to live shorter lives than those born in 2016 or those born in 2015. For the first time since World War I, the Centers for Disease Control and Prevention revealed on Thursday, the life expectancy of Americans at birth has dropped for three straight years.

Why? In part because of two other trends detailed in reports released by the CDC: an increase in suicides and a surge in drug-overdose deaths.

Included in those reports are analyses of how suicide and overdose deaths have changed over time. The increase in suicides, the data indicates, has been steady since 1999, accelerating slightly faster after 2006. (As population grows, more deaths by each cause are to be expected.) Overdose deaths also increased steadily, skyrocketing a few years ago.

Men are much more likely than women to die by suicide or overdose.

The increase in overdose deaths is a function of the increase in deaths from opioid abuse — itself a function of the spike in abuse of synthetic opioids like fentanyl. (The numbers for synthetics below exclude methadone.)

The best that can be said about the 2017 data on overdose deaths — surging past 70,000, far more than the historic peaks of car accident or HIV-related deaths in any year — is that the rate of increase slowed. The number of deaths linked to synthetic opioids was 50 percent higher in 2017 than in 2016 after doubling from 2015 to 2016. Of course, the increase in the number of deaths by 2016 meant that the number by which synthetic opioid deaths increased from 2016 to 2017 was about equal to the total number of synthetic opioid deaths in 2015 overall.

These deaths are not distributed evenly across the United States: A string of states from Maine to Kentucky — broadly following the spine of the Appalachian Mountains — saw some of the highest rates of overdose deaths in the nation.

In 1999, the rate of deaths was highest among those ages 35 to 44. By 2017, rates among those ages 25 to 64 were about even — and two to three times the rate 18 years prior. Among those 55 to 64 in 1999, the rate of overdose death was only slightly higher than among those younger than 25. By 2017, that rate was itself nearly double the peak among all age groups 18 years prior.

Suicide rates have increased less dramatically. Among women, there were increases in every age group under age 75. Among men, the same was true, with bigger increases, especially among those ages 45 to 64.

There’s also an uneven geographic distribution of how suicide rates have increased. The CDC data shows that the increase in suicides has been much sharper in more rural communities than more urban ones.

The rate in the most rural communities is 53 percent higher than in 1999. The rate in the most urban communities was 16 percent higher. More than half of suicides are committed with firearms; rural Americans are much more likely to have a gun in their homes.

In 1999, about 46,000 Americans died of either suicide or drug overdoses. In 2017, more Americans than that died of suicide alone.