Cancer Linxian study

ATBC, Alpha Tocopherol Beta Carotene Prevention Study CARET, Beta Carotene and Retinol Efficacy Trial LCPS, Linxian Cancer Prevention Study PHS, Physicians Health Study PPP, Primary Prevention Project SCPS, Skin Cancer Prevention Study VACP, Vitamin A and Cancer Prevention WHS, Women s Health Study CHD, Coronary Heart Disease CVD, Cardiovascular disease. 

The results of a major epidemiological study of the geographical variations in the occurrence throughout China of a wide variety of different types of cancer have recently been published in the form of an atlas (146). One result of this survey was the revelation of a very high, but very localized, incidence of esophageal cancer in the Linxian valley of Henan province in northern China (146,147). Esophageal cancer also exhibits very high incidence in a number of other localities in both Asia and Africa (148), but the Chinese occurrence has so far attracted the most international attention. 

Because of inhalation of smoke, especially tobacco smoke, the lungs are the most likely sites of cancer from exposure to PAH compounds. However, these compounds are also found in foods cooked under direct exposure to pyrolysis conditions and are suspected of causing cancer in the alimentary canal. Extraordinarily high rates of esophageal cancer have been observed in Linxian, China, and may be attributable to PAHs from unvented cookstoves.13 In this study, the glucuronide conjugate of 1-hydroxypyrene was monitored as a biomarker of exposure to PAH compounds (Figure 13.11). 

Many of the randomized controlled trials (RCTs) investigating a protective role for antioxidant nutrients in cancer prevention (Table 3) have focused on / -carotene. A study in Linxian, China, of a rural population with poor nutritional status found that supplementation with a combination of / -carotene, selenium, and vitamin E for 5 years provided a 21% reduction in stomach cancer mortality and a 13% reduction in all cancer deaths. Although interesting, the population studied was likely to have very low intakes of a number of micronutrients and this study does not contribute to knowledge about the effects of individual antioxidants or offer any insight into their effects on populations with good nutritional status. 

There are no published RCTs of vitamin C alone in primary prevention, but data from the small number of trials of vitamin C in combination with other nutrients have not provided any support for a role for high-dose vitamin C supplementation in cancer prevention (Table 3). The Linxian trial found no significant effect of supplementing Chinese men and women with 120 mg vitamin C and 30 pg molybdenum daily for 5 years on the risk of cancers of the oesophagus or stomach. The Polyp Prevention Study, a trial of 864 patients with previous adenoma, found no effect of either /3-carotene or a combination of vitamins E and C (1000 mg) on the incidence of subsequent colorectal adenomas. The Heart Protection Study also found no beneficial effects of supplementation with these three vitamins on cancer mortality. However, trials have generally... 

The Linxian, China, intervention trial provided evidence that nutritional supplementation may lower the risk of certain cancers. A modest but significant reduction in cancer mortality was observed in a general population trial in those receiving daily (for 5.25 years) a combination of /3-carotene (15 mg), vitamin E (30 mg), and selenium (50 pg). The subjects who received this mixture had a 13% lower incidence of cancer and a 10% lower mortality from stomach and oesophageal cancer than did the subjects who did not receive the mixture. In the ATBC study, male smokers who took vitamin E supplements had a 34% lower incidence of prostate cancer and 41% lower mortality from prostate cancer than did those who did not take the supplements. In the United States, in a nested case-control study conducted to examine the association of a-tocopherol, 7-tocopherol, and selenium with the incidence of prostate cancer, a striking fivefold reduction in risk was observed for the men in the highest quintile of 7-tocopherol compared with those in the lowest. Overall, evidence for the protection from cancer by vitamin E is not compelling. 

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