In a large study that followed more than 54,000 Danish adults for up to 27 years, researchers examined how nitrate and nitrite intake from different sources related to the development of dementia, including early-onset dementia. Their findings revealed a striking contrast. Higher nitrate intake from vegetables was associated with a lower risk of dementia, while greater exposure to nitrate and nitrite from animal products, processed meats, and drinking water was linked to a higher risk.

Dementia is influenced by a combination of genetic and lifestyle factors, but researchers say diet may be another important piece of the puzzle.

Vegetable Nitrate Linked to Lower Dementia Risk

According to ECU Associate Professor Catherine Bondonno, the protective effect associated with nitrate-rich vegetables may be related to how the body processes nitrate.

"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.

The researchers believe that the combination of nitrate, vitamins, and antioxidants found naturally in vegetables may help support brain health. Animal-based foods do not provide the same protective compounds and may encourage the formation of potentially harmful substances.

Dr. Bondonno said one practical takeaway from the findings is relatively simple. Participants who consumed higher amounts of vegetable-derived nitrate, roughly equivalent to one cup of baby spinach per day, experienced a lower risk of dementia.

By contrast, higher intake of nitrate from animal foods, especially red and processed meats, was associated with an increased 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.

Drinking Water Nitrate Raises New Questions

The study also identified a link between nitrate in drinking water and dementia risk, marking the first time researchers have reported such an association.

Participants exposed to nitrate in drinking water, even at concentrations below current regulatory limits, experienced higher rates of dementia. However, Dr. Bondonno emphasized that additional research is needed before drawing firm conclusions.

"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 across the European Union, the current limit for nitrate in groundwater and drinking water is 50 mg/L. Researchers observed a higher dementia risk among people exposed to water containing nitrate concentrations as low as 5 mg per liter.

Despite the findings, the researchers stress that people should not stop drinking water.

"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."

Study Shows Associations, Not Cause and Effect

The researchers caution that the study was observational, meaning it can identify associations but cannot prove that nitrate directly causes dementia.

As a result, the findings will need to be confirmed in additional studies. The team also notes that other aspects of participants' diets, lifestyles, or health could have contributed to the observed relationships.

Even so, the results suggest that where nitrate comes from may matter just as much, if not more, than how much is consumed. While nitrate from vegetables was linked to a lower risk of dementia, nitrate and nitrite from processed meats, animal products, and drinking water were associated with a higher risk, highlighting the importance of considering dietary sources when evaluating long-term brain health.