Nitrate in drinking water linked to increased dementia risk while nitrate from vegetables is linked to a lower risk, researchers find 

New research from Edith Cowan University (ECU) and the Danish Cancer Research Institute (DCRI) investigated the association between the intake of nitrate and nitrite from a wide range of different sources, and the associated risk of dementia.

Dementia is a complex disease shaped by both genetics and lifestyle, and Post-Doctoral Research Fellow at ECU’s Nutrition & Health Innovation Research Institute (NHIRI) and the DCRI, Dr Nicola Bondonno said dietary factors could also be important.

The research, which investigated the association between source-specific nitrate and nitrite intake and incident and early-onset dementia, followed more than 54,000 Danish adults for up to 27 years and found that the source of nitrate was of critical importance in a diet.

The researchers found that people who ate more nitrate from vegetables had a lower risk of developing dementia, while those who consumed more nitrate and nitrite from animal foods, processed meats, and drinking water, had a higher risk of dementia.

ECU Associate Professor Catherine Bondonno said that nitrate intake from vegetables has been linked with a lower risk of dementia, which is thought to be a result of the conversion of nitrate to nitric oxide in the body.

“When we eat nitrate-rich vegetables, we are also eating vitamins and antioxidants which are thought to help nitrate form the beneficial compound, nitric oxide, while blocking it from forming N-nitrosamines which are carcinogenic and potentially damaging to the brain.

“Unlike vegetables, animal-based foods don't contain these antioxidants. In addition, meat also contains compounds such as heme iron which may actually increase the formation of N-nitrosamines. We think this is why nitrate from different sources has opposite effects on brain health, but we need laboratory studies to confirm exactly what's happening,” she said.

This is the first time that nitrate from drinking water has been linked to higher risks of dementia. The study found that participants exposed to drinking-water nitrate at levels below the current regulatory limits, had a higher rate of dementia, however, Dr Bondonno stressed that this was only one study, and more research was required.

“Water doesn't contain antioxidants that can block formation of N-nitrosamines. Without these protective compounds, nitrate in drinking water may form N-nitrosamines in the body,” she said.

In Denmark and the EU, the limit for nitrate in groundwater and drinking water is set at 50 mg/L, but the researchers observed a higher risk for drinking water containing as low as 5 mg of nitrate per litre.

“Importantly, our results do not mean that people should stop drinking water. The increase in risk at an individual level is very small, and drinking water is much better for your health than sugary drinks like juices and soft drinks. However, our findings do suggest that regulatory agencies should re-examine current limits and better understand how long-term, low-level exposure affects brain health.”

She simultaneously emphasises that this is an observational study, which cannot establish that nitrate directly causes dementia. The results must therefore be confirmed in other studies, and it cannot be ruled out that other factors in participants' diets or lifestyles contribute to the association.

Dr Bondonno said the take-home results from the study is fairly simple: people who consume more nitrate from vegetables, equating to around one cup a day of baby spinach, had a lower risk of dementia.

On the other hand, people who consumed more nitrate from animal-based foods, particularly red and processed meat, had a higher risk.

“Eating more vegetables and less red meat and processed meat is a sensible approach based on our findings and decades of other research on diet and health,” she added.