Nitrate INFORMER Nitrosamine Study

Overview

Nitrate is a controversial component of vegetables, meat, and drinking water. The now well-established benefits of nitrate, through the enterosalivary nitrate-nitrite-nitric oxide (NO) pathway, on cardiovascular risk factors and long-term cardiovascular disease risk are tarnished by a continuing concern about a link between nitrate ingestion and cancer. This can result in misguided advice to avoid consumption of high-nitrate leafy green vegetables by both the media and the scientific literature. A recent media headline stated, "Cancer alert over rocket: trendy salad leaves exceed safe levels of carcinogenic nitrates in one in every ten samples". One scientific review stated, "the presence of nitrate in vegetables, as in water and generally in other foods, is a serious threat to man's health". Controversy in the literature, and gaps in the knowledge are leading to confusing messages around vegetables that may play a critical role in cardiovascular health. The major dietary sources of nitrate are vegetables, meat, and drinking water. Source of nitrate could be a crucial factor determining whether the consumption of nitrate is linked with beneficial (such as improving cardiovascular health) versus harmful (N-nitrosamine formation) effects. For example, unlike meat and water-derived nitrate, vegetables contain high levels of vitamin C and/or polyphenols that may inhibit the production of N-nitrosamines. So far, no study has investigated the formation of N-nitrosamines after consumption of these different sources in humans. A pilot study will be conducted to determine that endogenous N-nitrosamine formation is observed after ingestion of meat with added nitrate and nitrite and that consumption of vegetables with the meat containing added nitrate and nitrite will inhibit the production of N-nitrosamines.

Study design: A crossover study design will be used with a 1-week washout period. Each participant will complete the scheduled study visits for one of the dietary interventions which will be assigned in random order. Following the washout, the participants will then complete the scheduled study visits for the remaining intervention. Participants will be provided with a low nitrate and N-nitrosamine meal on the preceding evening of each study visit. These meals will be consistent across all study visits. Participants will be asked to refrain from drinking coffee and any alcoholic beverage and doing any exercise 24 hours prior to the study visit. Dietary interventions: Meat with added nitrate: Prosciutto/pancetta/Parma ham/salami (all derived from pork) prepared by a commercial butcher with sodium nitrate as an additive. Meat with added nitrate plus vegetables: The same intervention described above consumed together with mixed vegetables. Assessments: At each clinic visit, baseline samples of urine will be collected for measurement of N-nitrosamines, nitrate, and nitrite. After the intervention, all urine within the first 240 minutes and then subsequent 20-hour period will be collected for measurement of N-nitrosamines, nitrate, and nitrite.