Estimation of the potential for nitrosation and its inhibition in subjects from high‐ and low‐risk areas for esophageal cancer in southern China

We studied 2 counties in southern China, which are close to each other but show very different mortality rates from esophageal cancer. We collected 12 hr urine samples and analyzed them for NPRO, other nitrosamino acids, nitrate and ASC. The potential for forming NPRO and the effect on inhibition by ASC were recorded. Urine was collected after (i) no treatment, (ii) a dose of proline and (iii) proline with ASC. Intake and excretion of nitrate were significantly greater in the high‐risk area. After the proline dose, urinary excretion of NPRO was significantly greater in the high‐risk area. The inhibitory effect of ASC after taking it with proline was less in the high‐risk area. Hence, the high‐risk area showed greater potential for forming NPRO, and this formation was less inhibited by ASC. This supports the view that esophageal cancer in this area may be caused by nitrosamines formed in vivo, perhaps from nitrite produced by reduction of ingested nitrate. © 2003 Wiley‐Liss, Inc.