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National Institute of Environmental Health Sciences

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Preventing Disease through Healthy Environments: New World Health Organization Study Quantifies Impacts and Identifies Solutions

By Paula T. Whitacre

According to the recent study published by the World Health Organization (WHO) Preventing Disease through Modifiable Environmental Factors, 23 percent of worldwide deaths — 12.6 million children, women, and men — are due to modifiable environmental factors.

Preventing Disease Through Healthy Environments flyer
(Photo courtesy of WHO)

The authors looked at more than 100 diseases and injuries, including infectious diseases such as malaria and diarrhea; non-communicable diseases such as cancers and cardiovascular ailments; and injuries such as traffic accidents. They reviewed evidence to determine the extent to which interventions made in energy, agriculture, and other sectors, in addition to health, can reduce mortality. “The report’s unequivocal evidence should add impetus to coordinating global efforts to promote healthy environments — often through well-established, cost-effective interventions,” noted WHO in releasing the report.

“This is a critically important update to the 2006 WHO report that broke new ground by quantifying the burden of disease attributable to environmental factors,” said John Balbus, M.D., director of the NIEHS-WHO Collaborating Centre for Environmental Health Sciences. “At NIEHS, we try to focus our global research and research translation priorities on those environmental health issues responsible for the greatest burden of disease in low and middle income countries. This new report uses advances in epidemiological techniques to give a reliable and up-to-date guide for our efforts.”

Five authors coordinated the study: Annette Prüss-Ustün, Ph.D., Jennyfer Wolf, M.D., Carlos Corvalán, Ph.D., Robert Bos, M.Sc., and Maria Neira, M.D. They drew, in order of priority, from comparative risk assessment methods, epidemiological data, information about disease transmission pathways, and expert opinion, depending on the quality of data available for attribution of a specific disease or injury to environmental causes.

In the study, environment was defined as all the physical, chemical, and biological factors external to a person, and all related behaviors, but excluding those natural environments that cannot reasonably be modified. Five key results from Preventing Disease through Healthy Environments are:

  • Environmental disease accounts for a large fraction of the global burden of disease.
  • Environmental impacts are uneven across life course and gender.
  • Low- and middle-income countries bear the greatest share of environmental disease.
  • Total environmental deaths are unchanged since 2002, but a show a strong shift to noncommunicable diseases.
  • The evidence on quantitative links between health and the environment have increased.
Carlos Corvalán

Corvalán was one of five coauthors of the WHO publication.
(Photo courtesy of Carlos Corvalán)

In the Q&A below, Corvalán elaborates on some of the takeaways of the report for the global public health community.

Q: The report suggests ways to prevent death and disease through healthier environments. What are some interventions that struck you and your colleagues as particularly significant? Did anything surprise you?

Indeed, one valuable contribution of this report is that it is not just a quantification of the problem but provides examples of interventions that have proven positive to health, in some cases with quantified improvements.

Most interventions are quite common sense and are no surprise. Reduction in cookstove smoke in unventilated places, for example, will reduce respiratory infections; similarly, interventions that improve access to clean drinking water, sanitation, and hygiene practices help reduce diarrheal diseases.

Several interventions have an impact on non-communicable diseases (NCDs). For example, legislation to reduce second-hand tobacco smoke can have impacts on cardiovascular disease, while improved access to places that allow us to do physical activity, such as parks, are shown to be positive for mental health.

For each disease, the report attempted to identify different studies that quantified the reductions. In some cases, economic evaluations from the literature were also identified. Perhaps it is in these economic evaluations where the bigger surprises arise. For example, economic costs of premature deaths and disease from air pollution in Europe amount to $ 1.5 trillion USD.

Investing in healthy environments saves lives, but if that argument is not sufficient, the economic incentives should help.

Q: How might public/environmental health professionals, especially in low and middle income countries, use this report?

We picture it being useful in many ways. First, as evidence for action. It is a scientific tool and also an advocacy tool. It shows impacts and potential interventions. It points to costs and savings, showing how, most often, it makes good economic sense to invest in reducing environmental risks.

The report can also be used as a teaching tool, as it considers all diseases that can result from environmental risks and provides an up-to-date literature review.

Some specialists may attempt to do a national assessment of the burden of disease from environmental risks or make specific assessments of some key diseases, drawing from the report and its methodology.

Q: What is the most striking difference, in your opinion, between the findings from the 2006 report and the edition just published?

The 2006 study (based on 2002 data) and the 2016 study (based on 2012 data) have differences in methodology; therefore, comparisons need to be interpreted with care. We were able to use more robust methods in the 2016 study and had a larger volume of evidence available.

In spite of the differences, we can make some comparisons at the global level.

First, comparing the years 2002 and 2012, we see a decrease in the population-attributable fraction of death in the broad disease category of infectious, parasitic, neonatal, and nutritional diseases, from 31 percent to 20 percent. In the same period, however, we see an increase in the population-attributable fraction of death in NCDs, from 17 percent to 22 percent. The attributable fraction for injuries remained almost unchanged, increasing from 37 percent to 38 percent. This is consistent with the overall global trends in the transition of the burden of disease to NCDs.

Second, in the 2006 study, the top five diseases with the largest environmental contribution were, in order of importance: diarrhea, lower respiratory infections, other unintentional injures (which excludes road traffic accidents, poisonings, falls, fires, and drowning), malaria, and road traffic injuries. The top five in the 2016 study were stroke, ischemic heart disease, diarrheal diseases, lower respiratory infections, and cancers. Thus, the shift towards NCDs becomes clear. Interestingly, the total attributable fractions remained very similar: 23.3 percent in 2002 and 22.7 percent in 2012.

Another important difference is the impact on children. In 2012, 26 percent of all deaths in children under 5 could have been prevented if we could have removed all modifiable environmental risks. This figure was much larger in 2002, when we could have prevented up to 37 percent of all deaths in this age group.

Q: What do you see as the next step, such as research needed to fill in information gaps?

This study looked at the environmental determinants of health, but there is a parallel issue: the social determinants of health (WHO defines the social determinants of health, as the conditions in which people are born, grow, work, live, and age, and the wider set of forces and systems shaping the conditions of daily life). Environmental and social drivers of health are hard to disentangle and hard to measure separately. That remains a challenge.

Another issue is global environmental change. There is a large body of evidence regarding the well-known environmental risk factors such as water, sanitation, indoor fuel combustion, ambient air pollution, chemicals, and others. We are accumulating evidence on the health impacts of emerging risks such as climate change, loss of biodiversity, water scarcity and desertification, ecosystem damage, and other global impacts. It is in these emerging issues — the acceleration of global environmental change — where we may see important new evidence of quantifiable health impacts in the next decade. And that may still be our biggest surprise.