Researchers have presented updated data on the global disease burden caused by foodborne chemicals and toxins.
The data were discussed at a symposia in Arlington, VA, at the annual meeting of the Society for Risk Analysis. This past month the society updated a 2015 World Health Organization (WHO) publication that analyzed disease burdens caused by certain toxins.
Clark Carrington gave a talk on foodborne lead and contributions to decreased IQ in children. Dr. Chen Chen spoke about cassava cyanide, which is primarily a problem in Central Africa. Dr. Aron Barchowsky presented on foodborne arsenic and its impact on cancer and cardiovascular disease.
The global burden of disease from foodborne arsenic, lead, cadmium, and methylmercury was quantified and a summary paper published in 2019.
Methylmercury exposure from fish
Herman Gibb, of Gibb Epidemiology Consulting, found that in 2015, foodborne arsenic, methylmercury, lead and cadmium resulted in more than 1 million illnesses, 56,000 deaths and 9 million disability-adjusted life years (DALYs) worldwide.
“There have been a lot of papers on methylmercury. It has become even more of an issue because of small scale gold miners using mercury to mix with the gold, it forms an amalgam, they take that back to their house and heat it on their stove which drives the mercury off and leaves the gold,” he told Food Safety News.
“It is a common practice in West Africa, South America and Asia. But then that mercury deposits in the waterways and the fish take it up and people consume the fish. Methylmercury crosses the blood brain barrier so it is very toxic to a developing fetus.”
Gibb said guidance levels exist but there isn’t a benchmark to say whether the situation is getting better or worse.
“The way it has been measured in humans is the methylmercury concentrates in hair so by measuring the hair you can measure the mercury intake. The relationship with IQ is based on blood mercury but it is harder to take blood samples. It is a global problem but some regions are impacted more,” he said.
When the WHO work began, experts were associated with studies on bacteria, viruses and parasites but not many had knowledge of chemicals, said Gibb.
“It is a little bit harder to look at this as you see romaine lettuce contaminated with E. coli, people are worried about that, but you can say don’t buy it and when you go to a restaurant make sure they are not using romaine lettuce,” he said.
“Often with chemicals the effect takes a long time to develop, with arsenic you are not going to get ill tomorrow whereas with E. coli contaminated food you could. The number of DALYs is just as high if not higher for the chemicals. Part of that is because with methylmercury and lead the effect begins at an early age until death. Arsenic is associated with bladder and lung cancer and cadmium with chronic kidney disease.
“Eating food contaminated with Salmonella might make you sick for a week but usually you get over it. Trying to estimate the risk for chemicals can be harder as we are doing more of a dose response function as some effects don’t appear for some time.”
Gibb said the advice to people regarding methylmercury is not to avoid fish altogether.
“There are certain kinds of fish that have more methylmercury than others. These are usually the predator and bigger fish so swordfish and shark while trout and sardines are fairly low in methylmercury. You can watch what kind of fish you eat and limit intake so you are not eating fish every day. There are things that are beneficial. If you say don’t eat fish women are denying themselves omega-3 fatty acids and other helpful things.”
Many other chemicals in food could be examined, according to Gibb.
“We could look at aristolochic acid which is found in grain in the Balkans, people were developing cancer and nobody knew why and then they discovered it was aristolochic acid. The International Agency for Research on Cancer (IARC) concluded it was a known human carcinogen. Fish toxins would be another I would look at. The ones we tackled are where we thought the data were sufficient to make global and regional estimates. We would have done more if we had more resources.”
Felicia Wu, from Michigan State University, found that up to 155,000 annual liver cancer cases globally are caused by aflatoxin. Aflatoxin is a mycotoxin produced by mold that grows on corn and nuts, including peanuts and tree nuts such as almonds and pistachios.
Since 2007, WHO has had the Foodborne Disease Burden Epidemiology Reference Group (FERG). Gibb was an original member and chaired the Chemical and Toxins Task Force. Wu, Carrington, and Barchowsky were invited by this task force to prepare reports on aflatoxin, lead, and arsenic.
“The group of us were tasked to estimate the global burden of disease associated with chemicals and toxins in the food supply. At least in the U.S., they usually get less attention than foodborne disease outbreaks associated with Salmonella or E. coli, and yet these chemicals and toxins cause an enormous burden of disease and these can range from cancer, dysfunction of the immune system to cognitive impairment and cardiovascular diseases,” she told Food Safety News.
Scientists are learning that aflatoxin harms humans’ immune systems which can result in a impaired responses to infections. Studies seem to imply vaccine resistance. If exposed to a lot of aflatoxin in the diet and vaccinated against a particular disease, it is possible aflatoxin could reduce vaccine efficacy but this has not been confirmed. Wu’s research group has been studying the link between aflatoxin and disruption of the immune system with most of the work in 2019.
Wu said people are exposed to aflatoxin by consuming corn and peanuts as staples in the diet, typically in warmer climates.
“There hasn’t been enough attention in the past to see how the toxin increases the susceptibility of humans, especially children, to infectious diseases. Right now the primary cause of death in children under the age of five, aside from neo-natal reasons, is infectious diseases. Children whose immune systems are not fully developed cannot adequately deal with these infectious diseases and the mortality rates are very high,” she said.
“What I was interested in contributing to this conversation is they are also being exposed to a lot of aflatoxin and it may well be the case that if we are more careful about reducing or eliminating aflatoxin in their diets, that can bolster their immune systems to fight these infectious diseases and there could be a lower mortality rate.”
Food storage and climate issues
Wu was involved in a recently published a paper where samples of corn were taken from different households in southwest Nigeria.
“We found corn we sampled when it had just been freshly harvested could meet the U.S. FDA’s aflatoxin action levels, as they were quite low. But once that corn has been stored in warm and moist conditions for several months then the aflatoxin levels keep on climbing to extremely high levels. The reason for that is the fungi that produce aflatoxin thrive in storage and warm and moist conditions are typically associated with mold growth,” she said.
“There is a level of top down control with regulation or a food safety standard. However, there are bottom up interventions that can help reduce aflatoxin in the corn and nuts to begin with. These include things farmers can do in the field and improved food storage conditions.”
It is likely climate change is going to make aflatoxin problems worse as the suitable range for aspergillus fungi to grow, thrive and produce aflatoxin is going to spread further north and south, said Wu.
“In the U.S. a lot of the states where we are producing the most corn are further north, they don’t regularly have aflatoxin problems. If the climate continues to warm then we may see the spread of aflatoxin problems to those producers in the corn-belt.”
The link between aflatoxin and liver cancer has been known for close to 60 years but the study of the impact on the immune system is relatively new. Wu said it could turn out that aflatoxin affects human’s response to Salmonella or vice-versa with future interesting work looking at the combination of dietary toxins and microbes to see if there are any synergistic effects.
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