Throat cancer in Bomet linked to local soils

By Gatonye Gathura

Scientists have linked the exceptionally high rates of throat cancer in Bomet County to the local soils.

Their study has confirmed that residents with high levels of selenium, a nutrient found in soil, also be at high risk of a type of throat cancer called esophageal squamous cell carcinoma (ESCC)

But, this the scientists say is the opposite of what has been found elsewhere with people having low levels of selenium normally at highest risk of throat cancer.

“We found a positive association between higher serum selenium concentration and prevalence of ESD, an association contrary to our original hypothesis,” say the scientists who call for more investigations. ESD or esophageal squamous dysplasia are precursor lesion of ESCC

The study which involved 294 adults recruited within a 50 km radius of the Tenwek Mission Hospital, at Bomet Township, Kaganaiti, Koiwa and Mogogosiek was published on Friday (8th December) in the journal BMC Cancer.

This is one of several global efforts to understand the cause for high rates of throat cancer in Bomet and surrounding areas.

It involved researchers from Tenwek Mission Hospital in Bomet,  the US National Cancer Institute, University of Missouri, US and Mayo Clinic, US.

Kenya belongs to the African Esophageal Cancer Corridor (ESCC) which has the highest incidence of throat cancer in the world.

The corridor includes Malawi, Kenya, Uganda, Tanzania and parts of South Africa while other areas with high throat cancer incidence are China and Iran.

Various reports now indicate Kenya to have the highest rates of throat cancer in the world with Bomet and Eldoret increasingly seen as a significant hotspot.

Unlike elsewhere, throat cancer in the Rift Valley has also been seen to affect younger people and both genders in equal numbers. Normally data shows more men than women to develop throat cancer.

Aflatoxins in food, traditional grain alcohol and mursik, the traditional fermented milk of the Kalenjin, have been blamed for the high rates of throat cancer in the region.

But researchers say this does not tell the whole story hence the new study on selenium.

Several studies in China, Finland and elsewhere had found people with low levels of selenium to be at high risk of cancer suggesting if they increased intake they may be protected against the cancers.

Following these findings there has been an explosion of marketing of selenium diet supplements including in Kenya for protection against cancer.

Defending their findings in the Bomet study, the authors say it is the first to specifically look at the relationship between selenium and throat cancer in an African population.

Unlike other studies, in Bomet the author says they had actually measured selenium concentration in blood samples as opposed to estimating from food intake.

The researchers led by Natalie R. Pritchett of the National Cancer Institute collected blood samples for selenium testing while participants were also screened for throat cancer lesions.

Generally the study showed Bomet as an area of low selenium levels but varying from one location to the other.

People living in Bomet Township had the highest selenium concentration in their blood compared to those from Koiwa and Kaganaiti with participants from Mogogosiek having the lowest levels.

The results also showed that more people from areas of higher selenium concentrations had signs of throat cancer compared to participants from areas of lower concentrations.

“Selenium was found to be strongly associated with location of residence. The occurrence of ESD was also significantly associated with selenium concentration.”

Participants with symptoms of throat cancer, the study says had higher selenium concentration.

Selenium is a micro nutrient required by the body in small quantities and normally sourced from grains, leafy green vegetables, and animal products such as meat, fish, eggs, and dairy.

The soil level of selenium is reflected in locally grown plants and in animals and people who eat them.

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