Studying the history of mortality in developed countries helps people better understand its determinants (Cutler et al. 2006).
According to historical demographic data in developed countries, persistent mortality improvement since the Industrial Revolution was considerable (Horiuchi, 1999). The plummet of mortality could be attributed to several transitions occurring simultaneously and chronologically. Some research has suggested that better nutrition and economic growth led to centennial mortality decline since the mid- 18th century (McKeown, 1976; Fogel, 1994). After 1850s, efficient disease control got credits on mortality reduction as well. At that time, people believed that miasma which was emanated from rotting organic matters was the origin of diseases. As a result, a large-scale reform of sanitary engineering was implemented. After 1860s, as Pasteur identified the pathogens which were responsible for the epidemics, the germ theory of disease gained more attention and became widely accepted (Preston, 1996). The acceptance of germ theory then brought up pharmacological successes−the introduction of the sulfa drugs and penicillin in 1940s. Thereafter, infectious diseases became no longer the major fatal diseases and has been replaced by chronical diseases such as cardiovascular diseases (CVD) and respiratory diseases. In the second half of the 20th century, medical advance, which included effective treatment and well-established knowledge of the causation role of risk factors, and the promotion of a healthy lifestyle contributed to the sharp decline in cardiovascular disease (CVD) mortality (Cutler 2004; Cutler et al. 2006). And now, we are standing in the early 21st century and wondering what will be the next challenge in mortality improvement. I suggest to use the determinants of mortality as the framework to study mortality improvement. I will introduce x determinants: nutrition, public health, cell biology, and early-life factors in the following section.
Nutrition
McKeown (1976) was the first one who argued that improvements in quantity and quality of nutrition supply were the most important factors explaining mortality reduction in the 19th century. He pointed out that public health and modern medicine played little role during this period. Fogel (1994) supported McKeown’s views. He used Waaler surfaces to explain the linkage between height, weight, and mortality risk. Using clinical and epidemiological evidence he argued that early nutritional status was a good predictor of adult mortality rates. He posited that the population subsistence could be achieved at different levels where a population and a nutrition supply were in equilibrium, with some levels characterized by smaller people and higher mortality risk. Nevertheless, nutrition has been discredited by other empirical evidence. Historical data showed that mortality rates were not lower in well-fed population in the U.S. in the mid-19th century (Livi-Bacci, 1991). Moreover, Dasgupta and Ray argued that children with severe diarrhea could only absorb a small amount of nutrition from food (Dasgupta and Ray, 1990).
Public Health
Public health played an important role in mortality improvement both by changing living conditions and by diffusing information on health issues. For example, research has shown that water purification contributed to half of mortality reduction in the U.S. in the early 20th century (Cutler and Miller, 2005). On the diffusion side, it has been documented that after the first publication of the Surgeon General’s report in 1964, the smoking rate started declining. Empirical data shows that the overall smoking rate has gradually declined since half century ago. Currently, public health keeps on facing challenges of obesity. The prevalence of obesity has been growing since 1980s. Olshansky et al. suggested that the gradual improvement in life expectancy in the U.S. will level off due to the life-shortening effect of obesity (Olshansky et al., 2005). Another potential public health problem is the emergence and the spread of communicable diseases. A larger scale of intra- and international migration will fuel the spread of microbes (Skeldon, 2013; Neiderud, 2015). The emergence of a pandemic and the increasing prevalence of infectious diseases, such as AIDS, might cause a larger number of deaths and result in a hump in the mortality trend (Olshansky et al., 2005). Take Ebola for example, it’s said that “Ebola virus disease is a painful reminder that an outbreak anywhere can be a risk everywhere” (Frieden et al., 2014). Although this kind of extreme case is unlikely to happen, it’s a source of uncertainty as well.
Cell Biology
After the discovery of the molecular structure of DNA by James Watson and Francis Crick in 1953, these molecules which carry genetic information have been widely studied. Finding this piece of gene puzzle has enabled researchers to study the inherited characteristics coding in DNA sequences. Research has shown that the exogenous environment can affect gene expression through epigenetic mechanisms, such as DNA methylation, which are related to the aging process and the development of chronical diseases (Alvarado et al., 2014). Hannum et al. found that some genetic markers had statistically significant associations between methylation fraction and age. Their predictive aging model is quite accurate with correlations between age and predicted age of 96% for the Caucasians and 91% for the Hispanics, with errors of 3.9 and 4.9 years respectively. They also found gender has greater contributions to aging than BMI, with methylome of men aging approximately 4% faster than that of women (Hannum et al., 2013). Moreover, some research has shed light on dietary therapy. Dominguez-Salas et al. found that maternal nutritional status has enduring impact on phenotype of the offspring through DNA methylation at metastable epialleles (Dominguez-Salas et al., 2014). Along the same lines Daniel and Tollefsbol found that the consumption of food with bioactive dietary compounds can influence epigenetic mechanisms (Daniel and Tollefsbol, 2015).
Early-Life Factors
Early-life factors have impact on mortality as well (Cutler et al. 2006). Research suggests that the fetal exposure in utero drives the health disparity at birth (Currie, 2011). Empirical evidence from the baby boomers after World War II (WWII) showed higher mortality rates. These health disparities would result in different mortality outcomes in later life that were passed down to the offspring (Mosley and Chen 1984). Moreover, damage to the body in early life may be irreversible and has something to do with the earlier onset of aging or a faster aging process. Social and physical exposures in early life will affect adult’s mortality via biological imprint and social pathways (Mosley and Chen, 1984; Montez et al., 2011).
Economic Impact on Mortality
The intermediate scenario in the 2015 OASDI Trustee Report, actuaries assumed that the future economic growth will be a continuance of the historical experience during the past 100 years. However, they suggested that the medical expenditure as a share of gross domestic product (GDP) will grow at a slower pace, and thus will lead to a slowdown in the mortality improvement (The OASDI Trustee Report, 2015). Their assumption could be supported by the case of Japan. After 1995, the mortality decline in Japan slowed down. Research suggested that economic stagnation and rising income inequality could be the reasons (Murray 2011). However, I cast doubt on whether a smaller growth rate of medical expenditure as a percentage of GDP would necessarily be an impediment to further mortality decline. Because, on one hand, the absolute amount of medical expenditure is still expected to grow. On the other hand, as the market shares of the healthcare and pharmaceutical industries enlarge, the larger economics of scale will contribute to lower production and service unit cost. Lower product cost may lead to the drop in the prices for the healthcare therapy and prescriptive drugs.