Møller H, Landt J, Pedersen E, Jensen P, Autrup H, Jensen O M
Danish Cancer Society, Danish Cancer Registry, Institute of Cancer Epidemiology, Copenhagen, Denmark.
Cancer Res. 1989 Jun 1;49(11):3117-21.
Increasing levels of nitrate in drinking water is of concern due to the possibility of an associated increase in long-term exposure to endogenously formed carcinogenic N-nitroso compounds. Excretion of N-nitrosoproline in 12-h overnight urine after intake of 500-mg L-proline was used to quantify the rate of endogenous nitrosation in 285 individuals in an area in northern Denmark with large variation in nitrate concentration of the drinking water. Nitrate intake was measured in a 24-h duplicate diet sample. The crude association between nitrate concentration in drinking water and rate of endogenous nitrosation in individuals is only weakly positive and not quite statistically significant (P = 0.08). The risk of having detectable nitrosation increases significantly with total nitrate intake and tobacco smoking. In nonsmokers, nitrosation is determined by nitrate intake. Smokers have increased nitrosation which does not depend on nitrate intake. Effect modification through dietary factors was evaluated and indicated a protective effect of tea consumption, while the effect of eating vegetables was not clear-cut. The experimental design (12-h urine sample; proline dose taken in the evening) is likely to underestimate the effect of nitrate in drinking water relatively to nitrate in the diet.
饮用水中硝酸盐含量的增加令人担忧，因为长期接触内源性形成的致癌性N-亚硝基化合物的可能性可能会随之增加。在丹麦北部一个饮用水硝酸盐浓度差异很大的地区，对285名个体摄入500毫克L-脯氨酸后12小时夜间尿液中N-亚硝基脯氨酸的排泄量进行了测定，以量化内源性亚硝化速率。通过24小时重复饮食样本测量硝酸盐摄入量。饮用水中硝酸盐浓度与个体内源性亚硝化速率之间的粗略关联仅呈弱阳性，且在统计学上不太显著（P = 0.08）。亚硝化可检测的风险随着总硝酸盐摄入量和吸烟量的增加而显著增加。在不吸烟者中，亚硝化由硝酸盐摄入量决定。吸烟者的亚硝化增加，且不依赖于硝酸盐摄入量。对饮食因素的效应修正进行了评估，结果表明饮茶具有保护作用，而食用蔬菜的作用并不明确。相对于饮食中的硝酸盐，该实验设计（12小时尿液样本；晚上服用脯氨酸剂量）可能会低估饮用水中硝酸盐的作用。
