Mortality Increase—Short-Term Pattern or Changing Trend?
THROUGHOUT MODERN HISTORY, mortality has steadily de-
creased. Remarkably, this improvement can be seen for all ages and
almost all major causes of deaths. In 2015, however, there was an un-
usual increase in mortality, which stayed relatively high through 2016.
According to the Centers for Disease
Control and Prevention (CDC), the age-adjusted population mortality rate in
the United States increased by 1. 2 percent from 2014 to 2015. In the United
Kingdom during this same time period,
it increased by 4. 2 percent, according to
the Office for National Statistics (ONS).
In a significant deviation from the recent
trend, both resulted in a decrease in life
expectancy. Similar increases in deaths
have been reported in many other countries including France, Spain, Denmark,
This dramatic deviation from the
trend line demands further investigation. Is this just a short-term pattern, or
is it the beginning of a changing trend?
As with most questions related to population mortality, there are multiple
potential explanations and perspectives.
Which Causes of Death
In 2015/2016, there was no calamity
such as a natural disaster, pandemic, or
terrorist attack big enough to significantly change the population mortality
in the Western world. Nonetheless, the
increase in mortality can be seen for almost all age groups and major causes of
death (see Figure 1).
Some reports blamed the 2015 mortal-
ity increase on the flu, especially in the
U.K., where the flu vaccine was less ef-
fective than in the past. It was reported
that this relative ineffectiveness was due
to a unique strain of flu, which was wide-
ly circulated but was not included in the
But flu mortality only explains a small
fraction of the overall mortality increase.
Flu alone is a small cause of death. Flu
and pneumonia together represent 7
percent of total mortality and are re-
sponsible for 15. 4 percent of the total
In the United States, the 2014-2015 flu
was only moderately severe, and flu mortality was even less obvious than in the
U.K. to influence the overall mortality.
In the United States, mortality due to
drug poisoning—which fall into the
category of unintentional deaths—has
increased significantly in recent years.
From 2010 to 2015, drug poisoning mortality increased by 33 percent and today
is higher than road accident mortality.
Despite this worrying trend, it represents less than two percent of total
deaths in the United States. Extra mortality from drug poisoning explained
roughly 6. 6 percent of the total increase.
In the U.K., the drug poisoning mortality rate is less than half of that in the
United States, although the U.K. also saw
an increasing trend in recent years. Overall, it comprises a smaller portion, roughly
1. 2 percent of the 2015 mortality increase.
The largest cause of increase in the U.K.
is dementia. According to ONS, from
2013 to 2015, deaths from dementia in-
creased by 24 percent for those ages 75
and older. Dementia diagnosis rates,
however, increased just as dramatically.
In early 2013, one out of every two de-
mentia cases were properly diagnosed.
By early 2016, two out of three cases
are properly diagnosed[ 2] as a result of
strong government initiative in recent
years to increase dementia diagnosis and
Due to these improvements in diagnosis rates, much of the increase in dementia
mortality is not caused by an increase in
prevalence. Had these deaths not been
categorized as dementia, they would have
been spread among other causes. Nonetheless, as dementia largely affects the
elderly, much of the additional mortality
in 2015 comes from the older population.
The breakdown of mortality by cause
makes it clear that the 2015 mortality increase is unlikely from a random
cause-driven event. Rather, it is an overall change in mortality, indicating that
drivers more fundamental than randomness may be the culprit. Looking into the
drivers of mortality may provide additional insight.
Drivers Changing Mortality
One of the largest challenges facing
public health today is obesity. Today, the
United States has an adult obesity rate
of more than 35 percent; in the U.K, that
rate is more than 25 percent. While obe-
sity rates are still climbing, the increase
has been less persistent in the U.K., while
in the United States, the youth popula-
tion has shown signs of leveling off.[ 3, 4]
In order for obesity to be a direct
driver of the higher 2015 mortality rate,
however, there would have to be a sharp
increase in the obesity rate significantly
higher than historical increases. Obesity
rates in recent years did show increases,
but are well within the historic trend.
It should be cautioned that heterogeneity in obesity rates in different age
groups may show uneven patterns as
younger obese cohorts age. However, it
is unlikely that cohort movement would
explain a sudden short-term change in
mortality felt across age groups.