Higher intake of nitrates from plant foods was associated with a lower incidence of dementia, while nitrates from animal products and tap water were associated with a higher incidence. An international team that included researchers from Edith Cowan University identified this pattern. The study was published in the journal Alzheimer's & Dementia.

The researchers used data from 54,804 residents of Denmark who were between 50 and 64 years old when they joined the study. None had dementia at that time. Follow-up lasted up to approximately 27 years, with a median duration of 24 years.

Nitrate and nitrite intake was estimated using dietary questionnaires and food composition databases. For tap water, the researchers considered participants' residential address histories and water quality monitoring data. During follow-up, 4,750 cases of dementia were recorded.

People in the group with the highest intake of plant-derived nitrates had a 10% lower relative risk than those in the group with the lowest intake. Median intakes were 77 and 22 mg per day, respectively. The association was not linear: further increases in intake were not accompanied by a continuous reduction in risk.

For nitrates from animal products, meat products in which nitrate additives are permitted, and water, the association was in the opposite direction. The authors suggest that the food matrix matters: some conditions promote the formation of nitric oxide, which plays a role in blood vessel function, while others favor the formation of N-nitrosamines.