New research finds that the nitrate ingested over the course of a person’s adult lifetime through tap water and bottled water could be a risk factor for prostate cancer, according to a press release by the Barcelona Institute for Global Health (ISGlobal).
This finding is the conclusion of a study conducted in Spain and led by ISGlobal. The findings have been published in Environmental Health Perspectives.
Ingestion of waterborne nitrate, trihalomethanes
The aim of the study was to assess whether there was an association between the ingestion of waterborne nitrate and trihalomethanes (THMs) and the risk of prostate cancer. ISGlobal says that nitrate and THMs are two of the most common contaminants in drinking water.
The nitrate present in the water comes from agricultural fertilisers and manure from intensive livestock farming; it is washed into aquifers and rivers by rainfall.
THMs are by-products of water disinfection. Unlike nitrate, for which the only route of entry is ingestion, THMs can also be inhaled and absorbed through the skin while showering, swimming in pools or washing dishes. Long-term exposure to THMs has been associated with an increased risk of bladder cancer, but evidence of the relationship between THMs and other types of cancer is, to date, very limited.
The current maximum contaminant level (MCL) for nitrate in drinking water in the United States is 10 mg/L, as defined by the U.S. EPA to protect against blue baby syndrome. EPA has also said that total trihalomethanes (TTHM) have a maximum allowable annual average level of 80 parts per billion.
Prostate cancer
To evaluate the possible association between prostate cancer and long-term exposure to nitrate and THMs in drinking water, a research team led by ISGlobal studied 697 cases of prostate cancer in Spanish hospitals between 2008 and 2013 as well as a control group made up of 927 men aged 38-85 years who had not been diagnosed with cancer at the time of the study.
The average nitrate and trihalomethanes to which each participant had been exposed since the age of 18 was estimated based on where they had lived and the type (tap water, bottled water or, in some cases, well water) and amount of water they had drunk throughout their lives. Estimates were made on the basis of available data from drinking water controls carried out by municipalities or concessionary companies, from analyses of bottled water of the most widely distributed brands, and from measurements taken in different Spanish locations supplied by groundwater.
The findings showed that the higher the nitrate intake, the greater the association with prostate cancer. Participants with higher waterborne nitrate ingestion (lifetime average of more than 14 mg per day) were 1.6 times more likely to develop low-grade or medium-grade prostate cancer and nearly 3 times more likely to develop an aggressive prostate tumor than participants with lower nitrate intakes (lifetime average of less than 6 mg per day).
“It has been suggested that aggressive prostate cancers, which are associated with a worse prognosis, have different underlying aetiological causes than slow-growing tumours with an indolent course, and our findings confirm this possibility,” explained ISGlobal researcher Carolina Donat-Vargas, lead author of the study. “The risks associated with waterborne nitrate ingestion are already observed in people who consume water with nitrate levels below the maximum level allowed by European directives, which is 50 mg of nitrate per litre of water.”
Drinking water does not imply cancer
The authors noted that this study simply provides the first evidence of the association, which will need to be confirmed through further research. Therefore, there is still a long way to go before we can assert a causal relationship.
“Being exposed to nitrates through drinking water does not mean that you are going to develop prostate cancer,” commented Donat-Vargas. “Our hope is that this study, and others, will encourage a review of the levels of nitrate that are allowed in water, in order to ensure that there is no risk to human health.”
