A new cancer threat

Press, 24 February 1977, Page 16

A new cancer threat

By

ANTHONY TUCKER

in the “Guardian”

Intensive farming is leading to a world increasingly rich in nitrates and evidence has. been growing steadily that there may be an important correlation between nitrates in the diet and cancer. The cancer mechanisms involve the production within the body of highly active cancer-causing substances called N-nitroso compounds. As the need to provide low nitrate water for infants in some areas indicates, the general levels of nitrate in water and food are rising and the question now is at what point the increasing nitrate content of the diet poses an unacceptable increased risk of gastric cancer.

That, question can only be answered by extensive studies which show convincingly that the correlation between nitrate and increased cancer risk is real, ano also give some measure of the quantitative relationship between dietary nitrate and cancer incidence.

The first British study, carried out by scientists from St Mary’s Hospital Medical School and published in 1973, showed an anomalously high gastric cancer incidence in Worksop where nitrate levels in drinking water were then high (around 20 milligrams of nitrate nitrogen per litre, which is close to the recommended World Health Organisation maximum).

Since then studies carried out in Chile, where the use of agricultural fertiliser is high and most produce is marketed and eaten locally (unlike the centralised marketing system in Britain), have provided very powerful evidence of correlations between cancer incidence and local levels of fertiliser use.

These studies, published in 1975, suggested a direct relationship between cancer incidence and the cumulative exposure to nitrates, and an induction period for gastric cancer of between 15 and 20 years.

It is also believed that studies now under way in Japan, comparing gastric cancer incidence in popu-

lations on low-nitrate piped water supplies and groups on high-nifate well water are already indicating a strong correlation between cancer incidence and nitrate intake.

According to experts in Britain it is impossible from the available evidence to assess accurately the proportion of gastric cancers that can be attributed to nitrate — which at low concentrations is a natural component of water and vegetables — although assessments range from 10 per cent to about '5O per cent. But a detailed and careful

analysis of large groups of people is needed.

Hence the importance being attached to the proposed East Anglia survey, although the East Anglian water authority is at pains to emphasise that, even at the high nitrate water levels characteristic of some of the shallow' wells in its area, the risks are small. From a whole population point of view, however, it could be important in the long run because it might — if positive and convincing — result in policy changes in both agriculture and w'ater treatment.