[Paleopsych] NEJM: Deadweight?: The Influence of Obesity on Longevity

Fri Apr 15 20:44:29 UTC 2005

Deadweight?: The Influence of Obesity on Longevity

Volume 352:1135-1137	March 17, 2005 Number 11
http://content.nejm.org/cgi/content/short/352/11/1138

Samuel H. Preston, Ph.D.

[First, from CHE:
A glance at the current issue of The New England Journal of Medicine:
Eating into life expectancy

For the first time in two centuries, life expectancy in the United
States may well drop over the next 50 years, all because of the sharp
rise in obesity, write S. Jay Olshansky, a professor of epidemiology and
biostatistics at the University of Illinois at Chicago, and several
colleagues. The problem is increasing in all major racial and ethnic
groups, all regions of the country, and all socioeconomic strata, but is
most pronounced in children and members of minority groups. Unless
obesity is reduced, the authors write, "the youth of today may, on
average, live less healthy and possibly even shorter lives than their
parents." Obesity will kill more people than will cancer or heart
attacks, they say, and over time it could shorten the average life
expectancy for all Americans by two to five years, and for obese people
by 12 to 15 years. Even today's life expectancy is four to nine months
shorter than it would be, the researchers say, if the two-thirds of
American adults who are obese or overweight would shed the extra pounds.
The effects of increased obesity, including rises in the incidence of
diabetes, heart attacks, and strokes, are likely to combine with other
factors that cut life expectancy, such as AIDS, antibiotic-resistant
pathogens, and a possible influenza pandemic, they say. Obesity may
undermine "dire predictions" about the future health of Social Security,
they predict. That is because those predictions have been based on
projected large increases in survival past 65 years of age, forecasts
that "appear to be premature," they say. The article, "A Potential
Decline in Life Expectancy in the United States in the 21st Century," is
available to subscribers, or for sale, at
http://content.nejm.org/cgi/content/short/352/11/1138

--Peter Monaghan

---------------------
Obesity has clearly become a major personal and public health problem
for Americans; it affects many aspects of our society. In this issue of
the Journal, Olshansky et al.
<http://content.nejm.org/cgi/content/full/352/11/1135#R1> make an
important contribution to national discussions of the future of
longevity by calling attention to the very substantial increase in the
prevalence and severity of obesity since 1980 and its consequences on
health and mortality. They estimate that the current life expectancy at
birth in the United States would be one third to three quarters of a
year higher if all overweight adults were to attain their ideal weight.

Although Olshansky et al. put obesity in the foreground of their vision
of the future, the background for their vision is at least as bleak.
They argue that past gains in life expectancy were largely a product of
saving the young, which is unrepeatable. They claim that advances in
life expectancy at older ages will be much smaller than in previous
decades and that demographers and actuaries fail to recognize the
disjunction and blindly continue to extrapolate the past into the
future. They add to this concern that AIDS, antibiotic-resistant
pathogens, and influenza pandemics represent additional threats to
health. In their scenario, our children may have lives shorter than our
own.

I believe that these background elements are excessively gloomy.
Decreases in the rate of death at older ages have been the principal
force driving American longevity for at least half a century, and they
show no signs of abating. Sixty percent of the 9.23-year increase in
life expectancy at birth between 1950 and 2002 is attributable to
decreases in mortality among persons above 50 years of age.
<http://content.nejm.org/cgi/content/full/352/11/1135#R2> Although
improvements in life expectancy among women have slowed in the past
decade, improvements among men have accelerated. The mean of male and
female life expectancies at 65 years of age grew by 0.081 year per
calendar year between 1950 and 1990, and by an identical 0.081 year per
year between 1990 and 2002, the last year for which official U.S. life
tables have been prepared.
<http://content.nejm.org/cgi/content/full/352/11/1135#R3>

Demographers and actuaries use extrapolation to project the future of
life expectancy because it seems to work better than any alternatives.
<http://content.nejm.org/cgi/content/full/352/11/1135#R4>,
<http://content.nejm.org/cgi/content/full/352/11/1135#R5>,
<http://content.nejm.org/cgi/content/full/352/11/1135#R6> The biggest
mistake, which has been made repeatedly in projections of mortality in
the past, is to assume that life expectancy is close to a biologic
maximum. <http://content.nejm.org/cgi/content/full/352/11/1135#R7>
Confidence in the use of extrapolation is increased by the very steady
behavior of mortality trends themselves. The mean of life expectancies
at birth in 21 high-income countries shows a nearly perfect fit (a
coefficient of determination, R2, of 0.994) to a linear time trend
during the period from 1955 to 1996.
<http://content.nejm.org/cgi/content/full/352/11/1135#R8>

The effect of an increase in the prevalence and severity of obesity on
the longevity of U.S. citizens is already embedded in extrapolated
forecasts made in recent periods. In fact, these forecasts implicitly
assume that the severity of obesity will continue to worsen, and the
prevalence will rise, since it is the rate of change in the determinants
of mortality, rather than the level, that drives projected changes in
life expectancy. Hundreds of factors affect a population's rate of death
in any particular period, and it is their combined effect that
establishes the trend.

Although Olshansky et al. cite threats to future improvements in life
expectancy, it is important to recognize that many factors are at work
to maintain a steady pace of advance. These include medical research
organizations whose products have, for example, been responsible for
much of the massive decrease in the rates of death from cardiovascular
causes during the past four decades.
<http://content.nejm.org/cgi/content/full/352/11/1135#R9> Public support
for the National Institutes of Health remains very strong, and private
companies will continue to have incentives to develop new products that
enhance health and longevity. Longevity seems to have a strong genetic
component, 10 <http://content.nejm.org/cgi/content/full/352/11/1135#R10>
which holds out the possibility that genetic engineering may, sometime
within the 75-year projection of the Social Security Administration,
begin to enhance longevity.

Other positive influences on longevity are embodied in cohorts of young
persons who are approaching the ages at which death occurs most commonly
and who will presumably enjoy greater protection from many diseases than
will the people who have already reached those ages. Younger cohorts are
better educated than older cohorts, and mortality is profoundly
influenced by education. In 1998, life expectancy at age 25 was 7.1
years higher for men with some college education than for men with only
a high-school education. For women, the discrepancy was 4.2 years. 11
<http://content.nejm.org/cgi/content/full/352/11/1135#R11>

Younger cohorts have had lives less scarred by infectious diseases,
which influence the development of many chronic diseases of adulthood.
12 <http://content.nejm.org/cgi/content/full/352/11/1135#R12>, 13
<http://content.nejm.org/cgi/content/full/352/11/1135#R13> Younger
cohorts have consumed fewer cigarettes at a given age than older
cohorts, and the effect of smoking is clearly manifested in the rates of
death of the general population. In fact, a large fraction of the
decrease in the rate of the decline in mortality among older women in
recent years is a result of the rising rate of death from lung cancer in
this group, which is a reflection of the delayed uptake of smoking among
women in comparison with men. 14
<http://content.nejm.org/cgi/content/full/352/11/1135#R14>, 15
<http://content.nejm.org/cgi/content/full/352/11/1135#R15> Significant
"cohort effects" have been demonstrated in the prevalence of
cardiovascular disease, emphysema, and arthritis, suggesting that
younger cohorts will have lower morbidity from these conditions as they
age. 16 <http://content.nejm.org/cgi/content/full/352/11/1135#R16>

Another reason to expect the longevity of U.S. citizens to continue to
increase is that some populations have achieved life spans far longer
than those of people in the United States, thus demonstrating what is
possible even with no further technological advances. Japan has achieved
a life expectancy of nearly 82 years, 4.5 years higher than that
achieved by the United States and higher than that projected by the
Social Security Administration for the United States for 2055. 17
<http://content.nejm.org/cgi/content/full/352/11/1135#R17>, 18
<http://content.nejm.org/cgi/content/full/352/11/1135#R18> Some
researchers have used a wide variety of data to suggest that within the
United States, subgroups with the healthiest lifestyles may have already
achieved life expectancies of 90 years or more. 19
<http://content.nejm.org/cgi/content/full/352/11/1135#R19>

But let me be clear. The rising prevalence and severity of obesity are
capable of offsetting the array of positive influences on longevity. How
likely is that to happen? One promising observation is that the recent
increase in the levels of obesity was produced by relatively few excess
calories in the typical daily diet. The consumption of a median of 30
excess calories a day produced the observed increase in weight during an
eight-year period for Americans 20 to 40 years of age. 20
<http://content.nejm.org/cgi/content/full/352/11/1135#R20> At the 90th
percentile of weight gain, the excess consumed was about 100 calories a
day. Reversing the increase in body mass might be accomplished through
small behavioral changes that fit relatively easily into most people's
lifestyles. The food and restaurant industries would be valuable allies
in this effort, and there are recent indications of their willingness to
cooperate. 21 <http://content.nejm.org/cgi/content/full/352/11/1135#R21>

The fact that the U.S. population has already shown the ability to shift
to healthier lifestyles is encouraging. Forty-two percent of U.S. adults
were smokers in 1965, as compared with 23 percent in 2001. 14
<http://content.nejm.org/cgi/content/full/352/11/1135#R14> The
percentage of Americans 20 to 74 years of age with high levels of serum
cholesterol fell from 33 percent in 1961 to 18 percent in 1999 and 2000.
14 <http://content.nejm.org/cgi/content/full/352/11/1135#R14> Primarily
because of behavioral changes, the incidence of AIDS has fallen by
nearly 50 percent since 1992. 22
<http://content.nejm.org/cgi/content/full/352/11/1135#R22> The
percentage of fatal crashes involving drunk drivers declined from 30
percent in 1982 to 17 percent in 1999. 23
<http://content.nejm.org/cgi/content/full/352/11/1135#R23> Each of these
improvements in risk factors was facilitated by national campaigns that
warned of the hazards of particular behaviors. 23
<http://content.nejm.org/cgi/content/full/352/11/1135#R23>

The time has come to consider another major campaign. Even though the
requisite behavioral changes may be small, they may be difficult to
accomplish. The fact that most health-related behaviors have improved
while obesity has worsened may be an indication of just how daunting the
prospect of reducing levels of obesity may be. The rising prevalence and
severity of obesity are already reducing life expectancy among the U.S.
population. A failure to address the problem could impede the
improvements in longevity that are otherwise in store.

I am indebted to John Wilmoth and Mitch Lazar for suggestions and
assistance.

Source Information

> From the Population Studies Center, University of Pennsylvania,
Philadelphia.

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