Environmental and dietary risk factors for nasopharyngeal carcinoma: a case-control study in Zangwu County, Guangxi, China

Abstract

Summary A case-control study was conducted on 88 incident cases of histologically confirmed undifferentiated nasopharyngeal carcinoma (NPC) in Zangwu County, China, and 176 age-sex-and neighbourhood-matched controls. The design of this study was defined after an anthropological survey on living habits in regions of high NPC incidence and the evidence of carcinogenic substances in some commonly consumed preserved foods. Subjects were interviewed regarding living conditions and diet in the year preceding the diagnosis of NPC and, with the help of their families, during childhood and weaning. After adjustment for a living conditions score to eliminate a confounding effect, an increased risk associated with consumption of salted fish during weaning and childhood was confirmed, especially for salted fish in rice porridge. The consumption of leafy vegetables was associated with a reduced risk for NPC, and consumption of melon seeds between 2 and 10 years of age with an increased risk. After multivariate analysis and adjustment according to the living conditions score, the consumption of salted fish in rice porridge before age 2 (OR = 3.8, P = 0.005), exposure to domestic woodfire (OR = 5.4, P = 0.01) and consumption of herbal tea (OR = 4.2, P = 0.02) were found to be independently related to the risk of NPC. The excess risk associated with the use of domestic wood fire increased if there were no windows in the house and with poor ventilation and cooking outside the house in a shack. As well as confirming the importance of the consumption of salted fish in childhood, this study has been the first to provide unequivocal evidence for two other factors implicated in increasing the risk of NPC in China, the adult consumption of traditional medicines (herbal tea) and exposure to domestic wood fumes.

Adulthood consumption of preserved and nonpreserved vegetables and the risk of nasopharyngeal carcinoma: A systematic review

“…14,31-34,37-42 The source of controls was populationbased in 11 studies, 12,14,[32][33][34][35][36][37]40,42,43 hospital-based in 4 studies 13,31,38,39 and not stated in 1 study. 41 Thirteen studies were conducted among Chinese residents of Asian countries; of these, 9 were conducted in China 12,31,34,35,[37][38][39][40][41] and the others were carried out in Taiwan, 33 Malaysia, 14,43 and Singapore. 13 The remaining 3 studies were conducted in the United States, 36 Algeria, 32 and Tunisia.…”

“…12,14,31,[33][34][35][36][37][38][39][40][41]43 Among the 13 studies, the association Seven studies reported on 3 or more categories of nonpreserved vegetable and NPC to assess for the presence of a doseresponse trend between vegetable intake and NPC (Table III). Three of these studies showed evidence of a decrease in the risk of NPC with greater intake of nonpreserved vegetables.…”

“…Eleven of the studies enrolled 150 cases or less, 12,32,[35][36][37][38][39][40][41][42] whereas the largest study was comprised of 935 cases. 34 Twelve studies stated that the NPC cases under study were histologically confirmed.…”

“…All of the studies matched or adjusted for age and gender, 10 matched or adjusted for area of residence, 12,14,[31][32][33][37][38][39][40]42 and 5 adjusted for intake of foods other than salted fish. 33,[36][37][38]41 Only 2 of the studies adjusted for salted fish intake 38,41 ; none adjusted for EBV.…”

“…13 The remaining 3 studies were conducted in the United States, 36 Algeria, 32 and Tunisia. 42 Dietary intake information was collected using a food-frequency questionnaire in 12 studies, [12][13][14]31,[33][34][35][36][37][40][41][42] a dietary history questionnaire in 2 studies, 38,39 and dietary recall in 1 study. 43 In 1 study, the type of instrument used to assess food intake was not specified.…”