From air pollution to smoking, which risk factors contribute the most to health loss?

Published May 16, 2024

Understanding the relationship between risk factors and health outcomes is key to improving health and developing evidence-based policy. The latest Global Burden of Disease Study (GBD) uses innovative new methods to analyze risk factors to health in more than 200 countries. We discuss the data with study author Dr. Michael Brauer of IHME and the University of British Columbia. 

This transcript has been lightly edited for clarity

Rhonda Stewart: Welcome to Global Health Insights, a podcast from IHME, the Institute for Health Metrics and Evaluation. I’m Rhonda Stewart. In this episode, we’ll hear from Dr. Michael Brauer, a Principal Research Scientist at IHME and a professor at the University of British Columbia, as he discusses new data on a wide variety of risk factors to health. These range from air pollution, to high body mass index, to smoking, to kidney dysfunction. The research is part of the Global Burden of Disease study, also known as GBD. GBD is the largest and most detailed scientific effort undertaken to quantify health trends. GBD provides a unique platform to compare the magnitude of diseases, injuries, and risk factors across age groups, sexes, countries, regions, and time for decision-makers. GBD provides a unique way to compare countries’ health progress to understand factors that impact health, including high blood pressure, cancer, and heart disease. Led by IHME at the University of Washington, GBD is a truly global effort, with more than 11,000 researchers from over 160 countries and territories participating in the most recent update. The latest GBD studies, out now, cover topics including fertility, causes of death, and differences in health loss between males and females. So, Dr. Brauer, tell us a little bit about some of the key findings of the study. Give us a brief overview.

Dr. Michael Brauer: So, first of all, when we look across the 88 risk factors that we evaluated, we see several that really stand out, and these stand out across all levels of socioeconomic development: those would be smoking, high systolic blood pressure, particulate matter air pollution, and high fasting plasma glucose, which is a marker for diabetes. We also see an increase, and it’s really concerning that it’s expanding across the globe, with high BMI [body mass index], so measures of obesity, and sort of a constellation of risk factors related to sedentary lifestyles and poor diets, so physical inactivity and high cholesterol levels, etc.

Rhonda Stewart: And tell us also, why did you separate the risk factors into three categories, and what are those categories?

Dr. Michael Brauer: So, one of the things that we’d like to do is take the trajectories of how risk factors have changed over the past 20 years, and that gives us a little bit of a window into where we think things will go into the future. And so when we did that, we’re looking at trends, and we see these groups which tell us both the successes as well as the challenges that we’ll face in the future. So, for example, the first group are a group of risk factors where we’ve really seen successes around the world. These are things especially related to maternal and childhood health, things related to water and sanitation, so access to clean drinking water, access to sanitation, household air pollution, use of dirty fuels – for example, cooking over an open fire – and then even things like secondhand smoke, where we’ve really made progress. And these are risk factors where basically we need to continue what we’re doing to decrease them dramatically. And there are even some newer ones, for example, trans fat, where we’ve seen a growing number of countries implement bans of trans fat. So these, again, are examples of successes.

The second group are a group of risk factors where we have seen reductions, so policies and actions have been implemented, but they’ve been insufficient to counteract this trend. Most of the world’s populations are getting older. And many of these risk factors are basically exacerbated by aging populations and increases in the baseline rates of disease. So, an example of that would be smoking. We have seen improvements in smoking, but as populations age, and even as populations grow and get older, smoking still is a big contributor to death and disability around the world. Another example would be many of our dietary risk factors. And then, for example, environmental risk factors such as lead, where again, we’ve seen big improvements in the exposure to lead. But as populations age, the impact of cardiovascular disease is basically worsening in most of the populations of the world. We need to accelerate the action. So we’re doing a lot with smoking. We know the multifaceted interventions work, for example, with smoking, but they need to be accelerated and broadened.

Then the third group is really the challenging group. These are groups of risk factors where the exposure to the risk factors is increasing. And then that is exacerbated by these demographic factors, the growing populations, the aging populations. Some examples of that would be high systolic blood pressure, and air pollution, especially particulate matter outdoor air pollution. And then this group of risk factors that I mentioned related to what we call metabolic syndrome, physical inactivity, high BMI, high fasting plasma glucose, and even some dietary factors such as intake of sugar-sweetened beverages, so those sodas and juices that have high amounts of sugar. Also, some things that were really concerning where we’re seeing big increases right now are not huge risk factors globally, but we’re seeing big increases. So things like drug use and warm temperatures related to climate change.

Rhonda Stewart: And let’s talk a little bit about climate change. That’s obviously an issue that is on many people’s minds. How is that topic covered in the paper?

Dr. Michael Brauer: So, we’re covering it in a rather limited way. All we’re including in this paper are the direct effects of temperature, and in two ways: temperatures that are too cold and temperatures that are too warm. And one interesting aspect of that is right now, actually colder temperatures are a bigger contributor to disease burden than warmer temperatures. As the climate warms, however, there’s this tendency to think that, well, it’s going to warm, and for those cold temperatures, we’re going to lessen the burden. And that is true to some extent, but it’s not enough to compensate for the increase in burden that we’re seeing as temperatures warm. So that is a concern. We already are seeing around a half a million deaths in 2021 attributable to warm temperatures. And looking at all the climate projections, we would expect that to increase into the future.

Now, there’s a whole host of what we would call indirect effects of climate change that are not yet included in the GBD. But this is ongoing work that we’re engaged in right now and hope to include in the future. And that would be things such as the effect of extreme weather events, so floods, storms. We’re especially interested also in some vector-borne diseases, so malaria and dengue. And then a big impact, which is very hard to actually study, is how climate change will affect where populations are distributed. Where will populations leave from due either to temperatures just being inhospitable or lack of local food production, and where will those populations actually go? And so this climate-induced migration is a key factor that we’re starting to work on and we would hope to include in future analyses.

Rhonda Stewart: When it comes to these risk factors, it sounds like it’s really impossible to study them in isolation because they do have impacts on so many other things. Also, when you talked about high body mass index, for example, it seems that that could be surprising to some people, given that malnutrition is still an issue in many parts of the world. Tell us a little bit about where some of the risk factors rank in terms of what the leading risk factors are that you found in the study.

Dr. Michael Brauer: In terms of countries that have lower income and lower sociodemographic development, it is some of those traditional risk factors. So we are still concerned with childhood malnutrition. Again, we’ve had huge improvements around the world, but in parts of the world, those still are the leading risk factors. So things like low birth weight, short gestation, childhood malnutrition, even though we have seen a lot of progress as we move toward the higher-income countries, that’s again where we’re really concerned with those factors related to metabolic syndrome – the physical inactivity, high systolic blood pressure, high cholesterol, high fasting plasma glucose. We are also seeing the world shifting, and in some ways, it’s a good thing. The world is shifting from those traditional risk factors, and they’re improving. But the world is now increasingly going to look like these higher-income countries and take on those problems. So again, it’s a little bit of a window into where the world is going.

Rhonda Stewart: And as we think about where the world is going, what are the policy implications of the research?

Dr. Michael Brauer: So that’s really one of the reasons that we broke it down into those three groups. It gives us an idea of not only where do we need to prioritize, but also where do we think we’re going to need to emphasize more into the future. And for many of these things, we do know what works. So again, we have seen success for smoking, we have seen success for lead, we’ve seen success for air pollution in high-income countries. And it’s really a matter of actually taking those same approaches and ratcheting them up and, in fact, putting them on a faster time scale because of these demographic factors. So the longer we wait, the more impact these risk factors are going to have. The one that is really, again, more challenging is this metabolic syndrome, because we really don’t have a lot of effective policies that have been proven right now. There’s a lot of work underway, there are a lot of good efforts, but it’s too early to say what is scalable, what is actually going to work globally. And that really is our big challenge in terms of how we are going to develop effective policies for what looks to be already leading risk factors or groups of risk factors in many countries of the world and increasingly will be so throughout the world.

Rhonda Stewart: Well, Mike, thanks so much. Details about the Global Burden of Disease study and a wide range of GBD-related resources can be found at