The prospective cohort study identified an inverse association between vegetable nitrate intakes of up to 60 milligrams per day (mg/day), and hospital admissions for cardiovascular disease (CVD).
Further work revealed a moderate to high nitrate intake was linked to a lower risk of ischemic heart disease (IHD), ischemic stroke and peripheral artery disease (PAD), attributed to the nitrate’s ability to maintain vascular tone that influences blood flow and BP.
“A higher vegetable nitrate intake was also associated with a lower baseline systolic blood pressure (SBP) and diastolic blood pressure (DBP),” the team wrote.
“Our results suggest that ensuring the consumption of nitrate-rich vegetables, corresponding to around 1 cup of green leafy vegetables, may lower the risk of CVD.”
The study used data taken from 53,150 participants who took part in the 23-year-long Danish Diet, Cancer, and Health Study.
During these follow-up years, 14,088 cases of incident CVD were recorded. They found that people who consumed the most nitrate-rich vegetables had about a 2.5 mmHg lower systolic blood pressure and between 12 to 26% lower risk of heart disease.
“Our results have shown that by simply eating one cup of raw (or half a cup of cooked) nitrate-rich vegetables each day, people may be able to significantly reduce their risk of cardiovascular disease," said lead researcher Dr Catherine Bondonno from New Edith Cowan University’s (ECU) Institute for Nutrition Research.
"The greatest reduction in risk was for peripheral artery disease (26%), a type of heart disease characterised by the narrowing of blood vessels of the legs, however we also found people had a lower risk of heart attacks, strokes and heart failure."
A further finding revealed that the optimum amount of nitrate-rich vegetables was one cup a day. Consuming more than this amount appeared not to offer additional health benefits.
"People don't need to be taking supplements to boost their nitrate levels because the study showed that one cup of leafy green vegetables each day is enough to reap the benefits for heart disease," Dr Bondonno added.
"We did not see further benefits in people who ate higher levels of nitrate rich vegetables."
In discussing the results and their significance the team suggested the primary mechanism that dietary nitrate may follow is via augmentation of Nitric Oxide (NO).
“Endothelium-derived NO maintains vascular tone influencing blood flow and BP,” they wrote.
“In the present study, baseline SBP explained 21.9% of the total association between vegetable nitrate intake and incident CVD, indicating that the effects of nitrate on BP reported in clinical trials, translate to a lower risk of incident CVD, but also that other mechanisms are in play.”
The team also considered a number of limitations of their research, namely the observational study status, which prevented the team from inferring causality or rule out residual or unmeasured confounding factors.
The researchers also said that although links between higher nitrate intake and lower risk of a hospital admission for CVD was still present after adjustment for lifestyle factors and other indicators of a healthy diet, determining nitrate effects alone could only be achieved via intervention studies.
“Furthermore, we were unable to investigate potential interactions with known inhibitors of the nitrate-nitrite-NO pathway, including antibacterial mouthwash and proton pump inhibitors,” they added.
Source: European Journal of Epidemiology
Published online: doi.org/10.1007/s10654-021-00747-3
“Vegetable nitrate intake, blood pressure and incident cardiovascular disease: Danish Diet, Cancer, and Health Study.”
Authors: Catherine Bondonno et al