A study has shown that eating vegetable nitrates, found mainly in green leafy vegetables and beetroot, may reduce the risk of developing early-stage age-related macular degeneration (AMD). Researchers at the Westmead Institute for Medical Research interviewed more than 2,000 Australian adults aged over 49 and followed them over a 15-year period.
The research showed that people who ate between 100 to 142 mgs of vegetable nitrates each day had a 35% lower risk of developing early AMD than people who ate less than 69mgs of vegetable nitrates each day.
Lead researcher Associate Professor Bamini Gopinath from the Westmead Institute and the University of Sydney said the link between vegetable nitrates and macular degeneration could have important implications. “This is the first time the effects of dietary nitrates on macular degeneration risk has been measured.
“Essentially we found that people who ate 100mg to 142mg of vegetable nitrates every day had a reduced risk of developing early signs of macular degeneration compared with people who ate fewer nitrates.
“If our findings are confirmed, incorporating a range of foods rich in dietary nitrates – like green leafy vegetables and beetroot – could be a simple strategy to reduce the risk of early macular degeneration,” Gopinath said. Spinach has approximately 20mg of nitrate per 100g, while beetroot has nearly 15mg of nitrate per 100g.
The research did not show any additional benefits for people who exceeded 142mgs of dietary nitrate each day. It also did not show any significant connections between vegetable nitrates and late stage AMD, or between non-vegetable nitrates and AMD risk.
One in seven Australians over 50 have some signs of macular degeneration. Age is the strongest known risk factor and the disease is more likely to occur after the age of 50. There is currently no cure for the disease.
The research compiled data from the Blue Mountains Eye Study, a benchmark population-based study that started in 1992. It is one of the world’s largest epidemiology studies, measuring diet and lifestyle factors against health outcomes and a range of chronic diseases.
“Our research aims to understand why eye diseases occur, as well as the genetic and environmental conditions that may threaten vision,” Gopinath concluded.
Background: Dietary nitrate, found predominantly in green leafy vegetables and beetroot, is a precursor of nitric oxide. Under- or overproduction of nitric oxide is implicated in the aetiology of several eye diseases. However, the potential influence of dietary nitrate intake on age-related macular degeneration (AMD) risk has not been assessed.
Objective: To investigate the temporal association between dietary nitrate intake (from both vegetable and nonvegetable sources) and the 15-year incidence of AMD, independent of potential confounders.
Design: A longitudinal cohort study conducted from 1992-1994 to 2007-2009.
Participants/setting: The Blue Mountains Eye Study is a population-based study of adults aged 49+ at baseline, from a region west of Sydney, Australia. At baseline, 2,856 participants with complete dietary data and AMD information were examined, and of these, 2,037 participants were re-examined 15 years later and thus included in incidence analysis.
Main outcomes measured: Incidence of AMD (main outcome) was assessed from retinal photographs. Dietary intake was assessed using a semiquantitative food-frequency questionnaire. Nitrate intake from vegetables and nonvegetable sources was calculated by use of a validated comprehensive database.
Results: After adjusting for age, sex, smoking, energy intake, fish consumption, and AMD risk alleles (complement factor H and age-related maculopathy susceptibility-2 single nucleotide polymorphisms), participants in the third quartile compared with those in the first quartile (reference group) of total nitrate and total vegetable nitrate intake had reduced risk of incident early AMD: odds ratio (OR) 0.61 (95% CI 0.41 to 0.90) and OR 0.65 (95% CI 0.44 to 0.96), respectively. Significant associations were not observed between the fourth vs first quartile of total nitrate and vegetable nitrate intake with incident early AMD: OR 0.74 (95% CI 0.51 to 1.08) and OR 0.69 (95% CI 0.47 to 1.00), respectively. Nonsignificant associations were also observed with 15-year incidence of late AMD and total nonvegetable nitrate intake.
Conclusions: These novel findings could have important implications, if the association between total nitrate intake and vegetable nitrate intake and 15-year incidence of early AMD is confirmed in other observational or intervention studies.
Bamini Gopinath, Gerald Liew, Annette Kifley, Joshua R. Lewis, Catherine Bondonno, Nichole Joachim, Jonathan M. Hodgson, Paul Mitchell