Smoking has long been linked to nasopharyngeal cancer (NPC).
But a local study published this month is throwing an unexpected food item to the mix: salted vegetables, which are commonly consumed here.
NPC, which develops in the area behind the nasal cavity and above the back of the throat, is the second most common cancer to hit men here between 15 and 34 years old.
The study, published in the Chinese Journal of Cancer, found that those who consumed salted vegetables at least once a week had four times the risk of developing NPC as compared to those who never or rarely ate salted vegetables.
"This finding is important because understanding the risk factors of NPC could potentially lead to changes in cancer prevention campaigns," said the study.
"The burden of NPC is a major public health concern here, and by knowing that the risk factors are modifiable, public health programmes may be better able in the future to reduce the burden of NPC by allocating resources and formulating population strategies accordingly."
The link between salted vegetables and NPC lies in the food fermentation process, said Dr Christopher Hobbs, an ear, neck and throat (ENT) specialist at Nobel ENT Head Neck & Thyroid Surgery Centre.
Salted vegetables refer to vegetables that are first fermented, then pickled with salt and brine.
During fermentation, compounds called nitrosamines are formed.
Dr Hobbs told The New Paper: "These chemicals form in the food during the preserving process through the addition of nitrite and nitrate salts.
"Most nitrosamines (either synthetic or naturally occurring) are carcinogenic."
These chemicals are also present in tobacco smoke and are known as tobacco-specific nitrosamines, he added.
Another possible cause is the activation of the Epstein-Barr Virus (EBV) by substances released during the food fermentation process, said oncologist Wong Seng Weng.
The medical director of The Cancer Centre told TNP: "The kind of nose cancer diagnosed in east Asia almost invariably involves the EBV. But the infection is far more common than the cancer.
"The EBV in those infected may be dormant until some substance created by fermentation reacts with the virus."
As the virus is found almost everywhere, Dr Hobbs said the EBV is no longer considered a risk factor.
"It is likely that other factors, such as the way a person's immune system deals with the virus, are responsible for initiating or promoting cancer development in the nasopharynx," he said.
Other risk factors to NPC include the male gender, Chinese ethnicity - particularly from southern China - and family history, Dr Hobbs added.
Smoking habits and genetic factors matter too, said Parkway Cancer Centre's Dr Tan Wu Meng. The consultant oncologist said: "One study showed that having a first-degree relative with NPC would increase the risk by seven times."
Is the study enough cause for caution?
All in moderation, said oncologists.
Dr Tan said: "Salted meat and vegetables are often found in the Asian diet, and it should still be reasonable to eat in moderation."
Dr Wong cautioned against introducing such food to children too early.
He said: "There is scientific data that the effect is worse if the exposure starts at a young age. For kids, if you don't introduce the food to them, they will never miss it."
This article was first published on Jan 16, 2017.
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