Exposure to aflatoxin, a group of toxins produced by mould that grows on cereals, spices, and nuts, could be behind up to 28% of global cases of the most common form of liver cancer, according to a risk assessment published in Environmental Health Perspectives. More than five billion people worldwide are exposed to uncontrolled levels of the toxin.

 

“Aflatoxin contamination in food is a serious global health problem, particularly in developing countries,” write Yan Liu and Felicia Wu from the University of Pittsburgh in Pennsylvania, USA. The toxin could account for 4–28% of all cases of hepatocellular carcinoma (HCC), with sub-Saharan Africa, South-East Asia, and China shouldering the heaviest burden.

 

Aflatoxin is produced by a fungus that can grow on food crops in tropical and subtropical climates. Maize and groundnuts, staple foods of many African and Asian diets, are most prone to having the mould. As many poor people living in these regions cannot afford a varied diet, potentially contaminated foods make up a significant proportion of their diets. People in these regions are also more likely to be infected with the hepatitis B virus, which raises the odds of developing aflatoxin-related liver cancer 30-fold compared with uninfected people.

 

Although it has been known for some time that aflatoxin is carcinogenic, this is the first study to estimate the proportion of liver cancer cases worldwide attributed to the exposure.

 

To come up with their estimate, Lui and Wu pooled national and regional data from published research to estimate maize and groundnut aflatoxin contamination levels in different world regions, as well as population size and hepatitis B prevalence for the same areas. They incorporated data, available from the WHO, on average maize and groundnut consumption in different regions of the world. Using a threshold level of aflatoxin exposure likely to cause cancer, which was devised by the Joint FAO/WHO Expert Committee on Food Additives, they estimated that the exposure is probably responsible for between 25,000 and 155,000 cases of HCC each year globally.

 

Yun Yun Gong, from the University of Leeds in the UK, says the findings suggest that aflatoxin is a key contributor to the number of cases of HCC reported worldwide. This is the first step towards quantifying the health risks posed by aflatoxin globally, he explains.

 

The results will alert scientists and policy makers to re-examine aflatoxin exposure limits, says Gong.

 

Authorities in many countries have set standards for aflatoxin levels in food. Although such standards are also in place in developing countries, where the population is typically exposed to the highest levels of aflatoxin and has a high burden of hepatitis B, they are seldom enforced due to lack of resources, say Lui and Wu. “Indeed, the food in subsistence farming and local food markets is rarely formally inspected,” they write. They calculate that halving a hypothetical limit of allowable aflatoxin contamination in foods would cut by 300 the cases of HCC per billion people living in countries at high risk of the disease.

 

Gong calls for “urgent action” to strengthen and enforce food aflatoxin regulation in these countries. The toxins are not only responsible for a higher risk of cancer, she says: impaired growth in children exposed to it over long periods of time is becoming a major concern among scientists.

 

The amount of aflatoxin that contaminates food can be reduced by drying and storing grains properly, explains Gong. Sorting and washing the grains before cooking can also reduce levels of the harmful substance. She believes that global prevention strategies should include education campaigns to improve the public’s awareness of the risks.

 

Lui and Wu suggest that increasing hepatitis B vaccination rates in the counties hardest hit would be “highly effective” at reducing aflatoxin-related HCC.

 

“While it is impossible to completely eliminate aflatoxin in food worldwide, it is possible to significantly reduce levels and dramatically reduce liver cancer incidence worldwide,” the authors conclude. “The challenge remains to deliver these interventions to places of the world where they are most needed.”