While the costs are dropping for extra years of life among children worldwide and adults in high-income countries, they are rising for adult males in lower-income countries.
Dr. Prabhat Jha, head of the hospital’s Centre for Global Health Research, and his colleagues took the Michaelis-Menten (MM) equation – a mathematical model first used to analyze enzyme kinetics in 1913 – and applied it to adult and child mortality at different incomes. Dr. Jha is also a professor in the Dalla Lana School of Public Health at the University of Toronto.
Dr. Jha and his colleagues at the U of T reasoned that just as enzymes catalyze many of the important functions in the human body (such as breaking down carbohydrates to simple sugars) or in industrial processes (like converting milk to cheese or grains to beer), “public health catalysts” can react with income to increase life expectancy.
Their results appear today in the new open access journal e-Life.
“Income directly enables certain technologies, immunization programs, epidemiological knowledge, education, and sanitation systems and other areas, which may themselves be interpreted as ‘catalysts’ — agents that accelerate the rate of a reaction without being fully consumed in the process,” the authors wrote.
They came up with a new parameter, critical income, which they defined as the level of income needed to achieve half of the life expectancy in high-income countries. For example, in 1970, the critical income for overall life expectancy (in inflation adjusted 2005 dollars) was $1.48 a day. By 2007, the critical income had fallen to $1.21 a day. In other words, a lower national income is needed to achieve a higher life expectancy now, compared to 40 years ago.
However, that good news is due mostly to improvements in children’s health and to increased life expectancy in high-income countries, the researchers said. For adults ages 15 to 59 in lower-income countries, critical income has actually risen since 1970. In other words, adults in low- and middle-income countries need to have higher incomes on average to add an extra year of life. Adult males in these countries are especially affected, though adult females also suffer..
“Under the current conditions, an approximate national income per capita of $2.20 per day would be required in 2007 to attain the same achievable adult male survival rate with $1.25 per day in 1970,” the authors wrote.
Dr. Jha and his colleagues noted that increases in smoking, especially among adult males, and HIV prevalence are responsible for part of the life expectancy gap. By contrast, worldwide attention to childhood health including much research on new technologies, vaccines and political attention mean a rosier future for children.
“It’s becoming cheaper and cheaper to save a child’s life,” Dr. Jha said. “It’s due to technology. The world has invested huge dollars and attention on research for powerful drugs, vaccines and strategies to reduce child deaths. We have not done the same for adults. If we did, adult survival would improve even more.”
Dr. Jha and his colleagues recommended that society invest in research and treatment of adult chronic disease, most notably the control of smoking and other risk factors for chronic diseases, and in low-cost, widely useful treatments for these diseases.
The other authors of the paper are chemical engineering PhD student Ryan Hum, Professor Anita McGahan of the Rotman School of Management and chemical engineering professor Yu-Ling Cheng, director of the university’s Centre for Global Engineering.
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