Increased life expectancy 'not benefitting everybody'

Life expectancy, which has risen dramatically in the past 40 years, is not benefitting everybody equally particularly adult males from low and middle-income countries are losing ground, researchers including Indian-origin scientists say.

People are living longer on average than they were in 1970, and those extra years of life are being achieved at lower cost, the researchers, led by U of T Chemical Engineering PhD candidate Ryan Hum, said.
However, the costs for an extra year of life among adult males in lower-income countries are rising, Hum and his colleagues say, while the costs for an extra year of life among children worldwide and for adults in high-income countries continues to drop.

Hum along with co-authors Yu-Ling Cheng, Prabhat Jha from the Dalla Lana School of Public Health and Anita McGahan of the Rotman School of Management made the discovery when they took the Michaelis-Menten (MM) equation - a well-known mathematical model first used to analyze enzyme kinetics in 1913 - and applied it to adult and child mortality at different incomes.

They reasoned that just as chemical catalysts affect enzyme velocity; the public health catalysts react with income to affect life expectancy.

"We noticed the similarity in the curvature and became fascinated with the beauty of the analogy," Hum said.

"The MM equation is standard curriculum for biochemistry, biology and most chemical engineering undergraduate students and we knew there could be added knowledge that we could decipher purely from the math," Hum said.

Hum and his colleagues concluded by recommending 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 low-cost, widely useful treatments for these diseases.

In the paper, the authors expand on the analogy between enzymes and incomes.

"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 researchers wrote.

They came up with a new parameter, critical income, which they define as the level of income needed to achieve half of the maximal overall life expectancy found in high-income countries.

However, that good news is due mostly to improvements in children's health and to increased life expectancy in high-income countries, the researchers say.

For adults (aged 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 in order to add an extra year of life.