Estimation of Dietary Nitrate Intake in a Representative UK cohort_V1

Dietary nitrate has been shown to have health benefits including lowering blood pressure and improving the health and elasticity of blood vessels. The main source of dietary nitrate in the human diet is vegetables. Drinking water is another important contributor to nitrate intake but the nitrate level of drinking water varies on a daily basis and between different water authorities in the UK. Furthermore, the data available on dietary analysis software on the levels of nitrate in vegetables and vegetable-based foods is very limited. Therefore, there is an urgent need to more accurately estimate the levels of dietary nitrate intake in the UK population, and determine how the level of intake from all dietary sources (vegetables and drinking water) relate to risk factors for developing heart disease.

This project aims to analyse biobanked urine samples collected during Years 1 to 8 of the National Diet and Nutrition Survey (NDNS), which is conducted in a representative sample of the UK population. We will measure the levels of nitrate and its break down products (metabolites) in urine by using HPLC to estimate the levels of intake of dietary nitrate in the study participants. In addition, we will determine the level of intake from the diet diaries of the study participants using our database of nitrate levels in vegetables and drinking water to estimate the dietary intake, and compare this data with the urine analysis as a potential biomarker of dietary intake.

The NDNS study participants have previously consented for their urine samples to be used for future tests relating to nutrition and health as long as these tests have been approved by a NHS ethics committee. We have been granted permission to analyse the urine samples by the NDNS Bioresource Panel but must first gain ethical approval before the samples can be released to us for

In this laboratory study, we will estimate the average dietary nitrate intake of each participant of the NDNS study using both the analyse of 2500 biobanked urine samples collected from participants of the National Diet and Nutrition Survey. As part of the consent process for the 24 h urine collection for the NDNS study (NREC reference number 07/H0604/113) participants were given the option to consent for any of their remaining urine samples to be used in tests relating to nutrition and health which had been approved by a NHS ethics committee.

The main inclusion criteria of this laboratory project are:

- Adults aged 19-64 y with a complete 4-day diet diary and a biobanked urine sample

For the dietary analysis, the nitrate levels of each food item consumed (mainly vegetables and drinking water) will be estimated using UK and European food nitrate values and from previously published studies in the literature. In addition, the nitrate content of drinking water will be estimated for each participant by contacting DWI and the local water suppliers in the UK to collect the quality control of the nitrate content of the drinking water in the UK. The nitrate and nitrite level data will be sent to the NatCen Social Research staff to match the data to each participant based on their postcode and the year the volunteers participated in the NDNS study.

To associate the estimated daily intake of dietary nitrate with health markers and risk factors for cardiovascular disease, analysis of covariance will be used to detect statistically significant differences between high and low nitrate containing diets with blood pressure and other risk factors for cardiovascular disease, controlling for age, sex and total energy intake (MJ). Post-hoc pair-wise analysis will detect differences between quartiles of dietary nitrate intake.

To compare the agreement of the urine nitrate data with the dietary nitrate data, statistical tests such as Bland Altman analysis and principal components analysis will be performed.

Eligibility Criteria:
Inclusion Criteria:

* Adults aged 19-64 y with a complete 4-day diet diary and a biobanked urine sample

Exclusion Criteria:

* not consented to the future analysis of the biobanked urine sample for nutrition and health research
* the diet diary was not completed
* insufficient urine sample available for the urinary nitrate and metabolite analysis.