Human Life Span – Summary

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The past two centuries have witnessed a significant degree of global warming, as the earth has recovered from the global chill of the Little Ice Age and entered the Modern Warm Period.  Simultaneously, the planet has seen an increase in its atmospheric CO2 concentration that has taken it to levels not experienced for eons.  What effects have these "twin evils" of the climate-alarmist crowd had on human health?  Although no one can give a precise quantitative answer to this question, it is possible to assess their relative importance by considering the history of human longevity.

Tuljapurkar et al. (2000) examined mortality over the period 1950-1994 in Canada, France, Germany (excluding the former East Germany), Italy, Japan, the United Kingdom, and the United States, finding that "in every country over this period, mortality at each age has declined exponentially at a roughly constant rate."  In discussing these findings, Horiuchi (2000) notes that the average lifespan of early humans was approximately 20 years, but that in the major industrialized countries it is now about 80 years, with the bulk of this increase having come in the past 150 years.  He then notes that "it was widely expected that as life expectancy became very high and approached the 'biological limit of human longevity,' the rapid 'mortality decline' would slow down and eventually level off," but he states the now obvious fact that "such a deceleration has not occurred."

"These findings give rise to two interrelated questions," says Horiuchi: (1) "Why has mortality decline not started to slow down?" and (2) "Will it continue into the future?"

Some points to note in attempting to answer these questions are the following.  First, in Horiuchi's words, "in the second half of the nineteenth century and the first half of the twentieth century, there were large decreases in the number of deaths from infectious and parasitic diseases, and from poor nutrition and disorders associated with pregnancy and childbirth," which led to large reductions in the deaths of infants, children and young adults.  In the second half of the twentieth century, however, Horiuchi notes that "mortality from degenerative diseases, most notably heart diseases and stroke, started to fall," and the reduction was most pronounced among the elderly.  Some suspected that this latter drop in mortality might have been achieved "through postponing the deaths of seriously ill people," but data from the United States demonstrate, in his words, that "the health of the elderly greatly improved in the 1980s and 1990s, suggesting that the extended length of life in old age is mainly due to better health rather than prolonged survival in sickness."

Providing additional support for this conclusion is the study of Manton and Gu (2001).  With the completion of the latest of the five National Long-Term Care Surveys of disability in U.S. citizens over 65 years of age -- which began in 1982 and extended to 1999 at the time of the writing of their paper -- these researchers were able to discern two most interesting trends: (1) disabilities in this age group decreased over the entire period studied, and (2) disabilities decreased at a rate that grew ever larger with the passing of time.

Specifically, over the entire 17-year period of record, there was an amazing relative decline in chronic disability of 25%, as the percentage of the over-65-years-of-age group that was disabled dropped from 26.2% in 1982 to 19.7% in 1999.  What is more, the percentage disability decline rate per year for the periods 1982-1989, 1989-1994 and 1994-1999 was 0.26, 0.38 and 0.56% per year, respectively.  Commenting on the ever-accelerating nature of this disability decline, the authors say "it is surprising, given the low level of disability in 1994, that the rate of improvement accelerated" over the most recent five-year interval.

With respect to the population of the entire planet, Oeppen and Vaupel (2002) report that "world life expectancy more than doubled over the past two centuries, from roughly 25 years to about 65 for men and 70 for women."  What is more, they note that "for 160 years, best-performance life expectancy has steadily increased by a quarter of a year per year," and they emphasize that this phenomenal trend "is so extraordinarily linear that it may be the most remarkable regularity of mass endeavor ever observed [our italics]."

These observations clearly demonstrate that if the increases in air temperature and CO2 concentration of the past two centuries were indeed bad for our health, their combined negative influence was miniscule compared to whatever else was at work in promoting this vast increase in worldwide human longevity; and it is that "whatever else" to which we now turn our attention.

To summarize to this point, in countries with highly developed market economies where good health care is readily available, deaths of infants, children and young adults have been dramatically reduced over the last century or so, to the point where average life expectancy is now largely determined by what happens to elderly people; and it is evident that under these circumstances, the elderly are living ever longer with the passing of time.  It is further evident that this phenomenon is likely due to ever-improving health in older people, which in turn is likely the result of continuing improvements in the abilities of their bodies to repair cellular damage caused by degenerative processes associated with old age, i.e., stresses caused by the reactive oxygen species that are generated by normal metabolism (Finkel and Holbrook, 2000).

What is responsible for this incredible lengthening of human life span?  It is probably a number of things acting in concert, with no single phenomenon overpowering the others.  Nevertheless, the multi-faceted force has operated with unwavering consistency since the inception of the Industrial Revolution, which leads us to wonder if the "twin evils" of the climate-alarmist crowd might actually be responsible for some portion of the longer and healthier lives that are being experienced by the planet's elderly.

With respect to global warming, we note that rising temperatures are responsible for the prolonging of many more lives at the cold end of the temperature spectrum than they are for the shortening of lives at the hot end of the temperature spectrum (see the many sub-headings under Health Effects (Temperature) in our Subject Index).  With respect to rising concentrations of atmospheric CO2, we likewise draw your attention to the many items archived in our Subject Index under the heading of Health Effects (CO2).  In addition, in what follows we briefly review some materials that illustrate some of the means by which elevated atmospheric CO2 concentrations may help to extend human life span.

Wentworth et al. (2003) report they found "evidence for the production of ozone in human disease," specifically noting that "signature products unique to cholesterol ozonolysis are present within atherosclerotic tissue at the time of carotid endarterectomy, suggesting that ozone production occurred during lesion development."  As Marx (2003) describes it, "researchers think that inflammation of blood vessels is a major instigator of plaque formation," that "ozone contributes to plaque formation by oxidizing cholesterol," and that the new findings "suggest new strategies for preventing atherosclerosis."  Further, according to Marx, Daniel Steinberg of the University of California, San Diego, says that although it's still too early to definitively state whether ozone production in plaques is a major contributor to atherosclerosis, he expresses his confidence that once we know for sure, we'll know which antioxidants will work in suppressing plaque formation.

Reactive oxygen species (ROS) generated during cellular metabolism or peroxidation of lipids and proteins also play a causative role in the pathogenesis of cancer, along with coronary heart disease (CHD), as demonstrated by Slaga et al. (1987), Frenkel (1992), Marnett (2000) and Zhao et al. (2000).  However, as noted by Yu et al. (2004), "antioxidant treatments may terminate ROS attacks and reduce the risks of CHD and cancer, as well as other ROS-related diseases such as Parkinson's disease (Neff, 1997; Chung et al., 1999; Wong et al., 1999; Espin et al., 2000; Merken and Beecher, 2000)."  As a result, they say that "developing functional foods rich in natural antioxidants may improve human nutrition and reduce the risks of ROS-associated health problems."

Consider, in this regard, the common strawberry. Wang et al. (2003) report that strawberries are especially good sources of natural antioxidants.  They say that "in addition to the usual nutrients, such as vitamins and minerals, strawberries are also rich in anthocyanins, flavonoids, and phenolic acids," and that "strawberries have shown a remarkably high scavenging activity toward chemically generated radicals, thus making them effective in inhibiting oxidation of human low-density lipoproteins (Heinonen et al., 1998)."  They also note that Wang and Jiao (2000) and Wang and Lin (2000) "have shown that strawberries have high oxygen radical absorbance activity against peroxyl radicals, superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen."  And they say that "anthocyanins have been reported to help reduce damage caused by free radical activity, such as low-density lipoprotein oxidation, platelet aggregation, and endothelium-dependent vasodilation of arteries (Heinonen et al., 1998; Rice-Evans and Miller, 1996)."

Our reason for citing all of this information is that Wang et al. (2003) have recently demonstrated that enriching the air with carbon dioxide increases both the concentrations and activities of many of these helpful substances.  They determined, for example, that strawberries had higher concentrations of ascorbic acid and glutathione when grown in CO2-enriched environments.  They also learned that "an enriched CO2 environment resulted in an increase in phenolic acid, flavonol, and anthocyanin contents of fruit."  For nine different flavonoids, in fact, there was a mean concentration increase of 55% in going from the ambient atmospheric CO2 concentration to ambient + 300 ppm CO2, and a mean concentration increase of 112% in going from ambient to ambient + 600 ppm CO2.  Also, they report that "high flavonol content was associated with high antioxidant activity."

There is little reason to doubt that similar concentration and activity increases in the same and additional important phytochemicals in other food crops would occur in response to the same increases in the air's CO2 concentration.  Indeed, the aerial fertilization effect of atmospheric CO2 enrichment is a near-universal phenomenon that operates among plants of all types, and it is very powerful.  Since the dawning of the Industrial Revolution, for example, the work of Mayeux et al. (1997) and Idso and Idso (2000) suggests that the concomitant historical increase in the air's CO2 content has led to mean yield increases of approximately 70% in C3 cereals, 28% in C4 cereals, 33% in fruits and melons, 62% in legumes, 67% in root and tuber crops, and 51% in vegetables, as described in our Editorial of 11 Jul 2001.  Hence, there must have been significant concomitant increases in the concentrations and activities of the various phytochemicals in these foods that act as described by Wang et al. (2003).

If we are right on this point, this phenomenon should have had a major impact on human health and, consequently, life span over the past two centuries; and when we look at the data pertaining to the subject, we see that something has definitely had such an influence.  Could that something have been the historical increase in the air's CO2 content?  We believe that it has clearly played some role in the remarkable extension of human life span that has accompanied the progression of the Industrial Revolution, but just how large a part is difficult to determine.  More research into the effects of atmospheric CO2 enrichment on various health-promoting substances in the foods we eat is definitely needed to help resolve this important question.  And with the stakes being as high as they are -- with climate alarmists wanting to curtail the anthropogenic CO2 emissions that may be bringing us huge health benefits -- that research should be a high priority item for both government and private funding alike.

References
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Finkel, T. and Holbrook, N.J.  2000.  Oxidants, oxidative stress and the biology of ageing.  Nature 408: 239-247.

Frenkel, K.  1992.  Carcinogen-mediated oxidant formation and oxidative DNA damage.  Pharmacology and Therapeutics 53: 127-166.

Heinonen, I.M., Meyer, A.S. and Frankel, E.N.  1998.  Antioxidant activity of berry phenolics on human low-density lipoprotein and liposome oxidation.  Journal of Agricultural and Food Chemistry 46: 4107-4112.

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Manton, K.G. and Gu, XL.  2001.  Changes in the prevalence of chronic disability in the United States black and nonblack population above age 65 from 1982 to 1999.  Proceedings of the National Academy of Science, USA 98: 6354-6359.

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