The question was deceptively simple: What would happen if the leading risk factors that contribute to death and disability were erased from the planet? The answer, according to an international research team led by HSPH's Majid Ezzati, is a huge gain in healthy years of life--more than nine years on average for every person in the world. In regions where health is the worst, as in parts of AIDs-ravaged sub-Saharan Africa, the gain would be as great as 16 years.

According to Ezzati, an assistant professor of international health, about half of all deaths and 40 percent of the total burden of disease globally can be linked to the combined hazards of 20 risk factors, all of them potentially preventable. Five heavyweights that alone account for a quarter of the world's disease burden are childhood and maternal underweight, unsafe sexual behavior, high blood pressure, tobacco, and alcohol.

Low-cost measures like sanitation and cleaner fuels would cut premature deaths dramatically, the researchers say in two papers published in The Lancet in 2002 and 2003. If the 20 major risks listed at right were removed, deaths from severe diarrhea would decline by approximately 90 percent, for example, while mortality from lower respiratory infections would fall by about 60 percent.

As important as the investigators' findings is how they framed their question. Health-risk researchers typically study one disease and one associated risk factor at a time. Because methods vary among scientific disciplines and countries, it is difficult to pool and compare risk estimates. Ezzati's team applied protocols consistently to all risks. They also examined risk factors in clusters to assess their combined effects.

The vision of public health is to look far beyond single diseases and risk factors, Ezzati says. "Taking a global view, we must ask: Where should we focus the totality of our limited resources?"

Reviewing the prevalence in rich and poor countries of health risks, together with all existing evidence on their hazards, collaborators from the World Health Organization and countries around the world created a tool useful for addressing such far-reaching questions as, What essential packages of interventions would significantly lower child mortality? and How best to monitor health risks in populations?

The Lancet studies highlight the profound and disproportionate effects leading health risks impose on the world's poorest people. For them, pollution from the indoor burning of wood, coal, and dung is a major cause of lung disease, while this risk is unknown in industrialized nations. The poor are also increasingly besieged by risk factors for diseases once associated with the affluent--obesity and tobacco use, for example.

Starting from a simple "what if" question, Ezzati and colleagues have thrust global health disparities into the spotlight. And they have pulled lesser but still important health threats, such as child sexual abuse, out of the shadows.

With the dissemination of these findings in the World Health Organization's 2002 World Health Report, health authorities and practitioners have become more aware of the tremendous public health benefits associated with prevention, Ezzati says. "We're bringing prevention in global health to the forefront by researching its potential impact in a systematic way."

Michael Floreak, a resident of Cambridge, Mass., writes about innovators in public health and medicine

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