Individuals with major depressive disorder (MDD) are observed to have reduced plasma nitrate levels and plasma nitric oxide (NO) metabolites (Chrapko et al., 2004; Garcia et al., 2011). Endothelial cell dependent dilation of vascular smooth muscle function has been observed to be blunted in adults with Major Depressive Disorder (MDD) and mediated by NO-dependent dilation (Greaney et al., 2019). Certain vegetables and fruits are particularly high in dietary nitrates, which is reduced to nitric oxide in the stomach, entering intravascular circulation, and acting as a potent dilator, blood pressure reducing, and vasoprotective substance (Webb et al., 2008). In older adults, dietary nitrates which are found in certain vegetables and fruits (e.g., green leafy vegetables) is shown to increase cerebral blood perfusion in frontal lobe white matter between the dorsolateral prefrontal and anterior cingulate cortex, regions particularly implicated in cognitive functioning (Presley et al., 2011). Recently, Morris et al. (2018) observed that in older adults from the Memory and Aging Project (MAP), the highest quintile of dietary nitrate intake was associated with slower cognitive decline than that of the lowest quintile of nitrate intake. Although viewing the extremes of dietary nitrate intake reveals valuable information, the present study investigated the association of all levels of dietary nitrate intake with cognition and depression among older adults in the same MAP dataset.

The sample included 461 community dwelling older adults (Mage=80; Medu =14.9, 74% female) from the MAP study (Bennett et al., 2012). The measures used for the present study include: the Center for Epidemiological Studies Depression Scale (CESD, depression), a neuropsychological battery (global cognition, perceptual organization and semantic memory), and a dietary nutrient analysis of the food frequency questionnaire (FFQ, nitrate).

Using Pearson correlations we observed that increased dietary nitrate intake was associated with increased global cognition (r(458) = .100, p = .031), perceptual organization (r(448) = .095, p = .04) and semantic memory (r(453) = .142, p = .002). Furthermore, we observed that dietary nitrate intake was associated with lower depression severity (r(459) = -.132, p = .004).

The present study’s results revealed that in a sample of community dwelling older adults, eating more nitrate rich foods is not only associated with improved cognition similar to findings of Morris et al. (2018), it is also associated with lower levels of depression. This further extends the Morris et al. (2018) study by suggesting that it is not only those older adults who eat the highest quantity of nitrate rich foods that can benefit from higher levels of nitrate intake. Overall, this study reveals that older adults who increase their dietary nitrate intake may improve their mood and thinking ability.