Food-Disease Links, from Genes to Global Impact
Felicia Wu is precise and patient as she explains the complexities of a measurement known as the “global burden of disease” – what factors are included, how it is calculated, why it is important. She has devoted some fifteen years to the concept, bringing her sharp analytical training to the most visceral of human challenges: safely feeding life on the planet.
“My research interests lie at the intersection of global public health, agriculture, and trade,” she explains. “How do agricultural systems affect health in different parts of the world? How do food safety regulations affect global trade of food, and ultimately food quality, particularly in low-income nations? What is the global burden of disease caused by food contaminants, and how cost-effective and feasible are interventions to improve food safety?”
A Kernel of Knowledge
In the late 1990s, Wu began her doctoral research at Carnegie Mellon on transgenic Bt corn, a type of maize that has been genetically modified to be resistant to insect pests. Several studies at the time had shown that genetically modified Bt corn had lower levels of mycotoxins, or fungal toxins – because there was less pest damage on the corn, there was less fungal infection.
“At first I thought, why do we even have to have genetically modified corn in the United States?” Wu says. “But as I dug deeper, I found out that there was actually this secondary, potential human and animal health benefit to genetically modified Bt corn, because it has lower mycotoxin levels.”
Bioengineering a particular type of crop or a particular type of animal – that is, developing genetically modified organisms (GMOs) – introduces new genes into the organisms, which in turn produce novel proteins. “Proteins are rarely toxic, or mutagenic or carcinogenic,” says Wu. “But the one real concern from a human health standpoint is, is the novel protein allergenic?”
Wu’s dissertation focused on how to improve regulation of Bt corn in the United States, with a focus on understanding the economic and health impacts under conditions of uncertainty to different stakeholders in the corn value chain.
From Science to Solutions
Much of Wu’s work now consists of translating toxicological and scientific results of dietary and environmental studies into policy and public health implications, evaluating the importance of a disease or a toxin and the losses in terms of human health. If there is already a regulation in place, she probes what the costs are – primarily to food producers – in meeting the regulation, versus the human health benefits that result from the regulation.
“I wanted to know what it would mean in terms of economic losses. If you set a particular standard, certain farmers aren’t going to be able to meet that standard,” she says. “If a farmer couldn’t meet that standard, he would have to sell his crops at a much lower price.
As for the public health angle, she explains: “Though a number of studies have examined how agricultural and food safety policies and practices and innovations affect nutrition, the researchers rarely go that extra step to ask what the human health impact of a particular agricultural innovation would be, or how much human disease might be reduced if better nutrition were introduced.”
Now she is using social network models to determine how food safety regulations set by different nations affect global patterns of food trade, and the corresponding impacts to the population health of different nations.
For Wu, it boils down to economics: The classic idea of costs, benefits, and tradeoffs is crucial to evaluating agricultural regulations and agricultural innovations, especially in low income nations. But it also includes health economics: valuing human life and well-being, how to measure human disease and human wellness, and how to evaluate agricultural innovations based on those benefits to health.
As a result of Wu’s expertise in food safety and health economics, she was chosen to be part of a World Health Organization initiative studying the global burden of human disease associated with contaminants in food, looking at different toxins that are in the food supply and how much toxins contribute to human disease, and putting that into health economics terms.
“Since the 1980s, the World Health Organization, which is part of the United Nations, has been interested in measuring global burden of human diseases,” she explains. “Assuming that different institutions and nations have limited resources, they have to decide where they are going to put their priorities. How can they make a decision between malaria, versus tuberculosis, versus AIDS/HIV, versus different cancers? How are they going to figure out how to allocate their efforts?”
The WHO initially struggled with how they were going to measure the global burden of disease, says Wu, because there were certain types of diseases that result in death, but death is not the only outcome that had to be considered.
There are diseases – for example, Type II Diabetes – that don’t result in death immediately, but cause some type of burden of disease for a long time and can lead to long-term complications, such as foot amputation or blindness or other illnesses that are not directly associated with death, but that cause a lot of suffering to the individuals that have them.”
So how does a policymaker valuate all of these things, from death to disability? The WHO economists, says Wu, came up with the term, “disability-adjusted life-year,” taking into account both mortality and morbidity associated with different diseases and conditions and injuries.
Disability-adjusted life-years are calculated both by the years of life lost if a person has a particular disease, injury, or condition, added to years lived with the disability. Then the number of years a person has the disease and is living with disability is multiplied by a disability weight, depending on how severe the disease is or how burdensome the condition is.
“For example,” says Wu, “I have a very mild case of asthma, so the disability weight is very close to zero. As a result, the number of years that I am living with this condition is multiplied by a very small disability weight.”
On the other hand, says Wu, if a person has a condition where she or he is paralyzed from the neck down, that has a much higher disability weight, so the number of years that person has to live with that particular condition is multiplied by a number much closer to one.
Global Burden of Disease
By 2006, the WHO’s initiative to find the global burden of disease was broadened to include the burden of disease caused by food contaminants. WHO organized the Foodborne Disease Epidemiology Reference Group to lead the new effort.
Wu has been commissioned by the group to estimate the burden of disease caused by aflatoxin (naturally occurring mycotoxins produced by Aspergillus flavus and Aspergillus parasiticus, two species of fungi) in the food supply. She serves on the computational task force for the group, trying to evaluate some of the diseases caused by food contaminants in terms of disability-adjusted life years.
But, cautions Wu, when assessing the dangers of food contaminants such as mycotoxins, context is everything. Or from Wu’s perspective as a mathematician, doing a risk assessment is a critical piece of any policy decision.
“If I were to contract a particular disease, just how bad would it be and how likely is it, based on what I am exposed to?” she asks. “That’s quantitative risk assessment – you have to consider dose response and exposure.
“On the exposure side it’s all about probability: how likely is it that I am exposed to this particular toxin or this particular adverse substance and what is the probability that I would ever be in a situation that this type of adverse event would occur?”
Wu says that, in terms of food contaminants, the probability of a having serious health effect is probably pretty low. “If you look at what the main types of health risks are in the U.S., if you look at cardiovascular diseases and cancers as a whole, those are things that one ought to be concerned about, not necessarily food borne toxins. I feel pretty good about how food is regulated in the U.S.”