The average life expectancy in the U.S. has been on the decline for three consecutive years.
A baby born in 2017 is expected to live to be 78.6 years old, which is down from 78.7 the year before, according to data from the Centers for Disease Control and Prevention's National Center for Health Statistics.
The last three years represent the longest consecutive decline in the American lifespan at birth since the period between 1915 and 1918, which included World War I and the Spanish Flu pandemic, events that killed many millions worldwide.
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Before the recent decline, life expectancy had been steadily rising in the U.S. — which is to be expected of an advanced nation, particularly one that spends more money per citizen on health care than any other country.
The U.S. isn't alone. A study projected the U.K. lifespan will shorten by about five months. While life expectancy is still on the rise in France, Germany, Sweden and the Netherlands, those countries have also seen a sharp slowdown.
While there's no single cause for the decline in the U.S., a report by the CDC highlights three factors contributing to the decline.
A rise in drug overdoses
In 2017, more than 70,000 deaths occurred because of drug overdoses. Opioids were involved in more than 47,000 of those.
The age-adjusted death rate for drug overdose in the U.S. rose 72% within a decade.
When the CDC analyzed data from emergency room visits, it found that opioid overdoses went up a whopping 30% in the U.S. from July 2016 and September 2017.
Opioids continue to be prescribed at triple the amount they were in 1999, but many are hoping to change that. The federal government has spent more than $2.4 billion in state grants since 2017 in a bid to curb the epidemic.
CDC data shows the number of opioid prescriptions, while still high, is now declining.
An increase in liver disease
Over a 10-year period, the death rate for chronic liver disease and cirrhosis among men aged 25 to 34 increased by nearly 8% per year, while women in the same age group increased more than 11% per year.
The causes of liver disease can vary, from genetics to alcohol consumption and obesity.
A rise in suicide rates
The national suicide rate has increased by 33% since 1999. In 2017 alone, that rate went up by 3.7%.
The global suicide rate, meanwhile, has declined by almost 30% since 2000, with the rates in Russia, Japan, South Korea and India falling significantly over the last decade.
This story first appeared on CNBC.com More from CNBC: