Exposure to nitrate from food and drinking-water in New Zealand. Can these be considered separately?

Recent epidemiological studies have reported associations between colorectal cancer incidence and nitrates in drinking-water, but not from the diet. The toxicokinetics of nitrates were reviewed and exposure data from New Zealand were analysed. Dietary (including drinking-water) exposure of New Zealanders to nitrates was found to be very similar to most other countries and within internationally-established acceptable daily intakes. Less than 10% of nitrate exposure was from drinking-water, with little difference between adults and children. Approximately half of the total water-based exposure is through water alone, the remainder was consumed as tea and coffee (adults), or water-based fruit drinks (children). For children, drinking-water as a beverage is generally consumed close to a meal time, with 83% of servings consumed within an hour of eating. For adults, this is reduced to 51% of servings consumed within an hour of a meal. Only 2.6% of nitrate exposure for adults and 0.7% of nitrate exposure for children is from drinking-water consumed on its own and not in close temporal association to food consumption. It was concluded from the combination of the biology and the exposure assessment that there is little reason to differentiate between drinking-water and food nitrate exposure.