Vegetable-rich diets are linked to lower risk of hypertension and dementia.
While the vitamins, minerals, and polyphenols in veggies probably help, new studies in brain health suggest an overlooked reason – nitrates – for these benefits.
The words “nitrite” and “nitrate” typically evoke thoughts of hot dogs, baloney, and cancer risk.
Processed red meats are often preserved with nitrites … and/or with nitrates, which bacteria in the human body convert to nitrites.
by nitrate content (mg/100 g)
< = less than, > = greater than
Indeed, nitrites are critical to human health and abound in some of the healthiest foods around … green and root vegetables.
Now a report from Wake Forest University affirms prior indications that dietary nitrates – in this case, from beet juice – ease blood flow to key parts of the brain, providing potential anti-dementia benefits (Presley TD et al. 2010).
Dietary nitrates appear to boost production of nitric oxide – a chemical the body uses to keep arteries relaxed and open.
Vegetables provide some 80 percent of dietary nitrates for most people ... and the new findings suggest that nitrate-rich veggies may be a key brain-health ally.
The nitrate content of vegetables varies with soil conditions and fertilizer use ... but to see which ones offer the most nitrate on average, see our sidebar, “Vegetables by nitrate content”.
Beet-borne nitrates boosted blood flow to key brain areas
Study lead author Daniel Kim-Shapiro, Ph.D., explained the motivation for the investigation:
“There have been several very high-profile studies showing that drinking beet juice can lower blood pressure, but we wanted to show that drinking beet juice also increases perfusion, or blood flow, to the brain.”
As we shall see, his next point is the critical one with regard to their findings: “There are areas in the brain that become poorly perfused as you age, and that's believed to be associated with dementia and poor cognition.”
His Wake Forest team recruited volunteers aged 67 to 81 (average 74.7 years old) and divided them into two groups.
Nitrates, meat, and cancer
The American Institute for Cancer Research recommends that people “Limit consumption of red meats such as beef, pork and lamb and avoid processed meats” (WCRF 2007).
A systematic review indicated that you can eat up to 18 oz weekly of red meat without raising your cancer risk.
However, cancer risk is shown to increase with eating any amount of processed meats regularly.
The nitrites added to meats can react with compounds in the body (secondary amines or N-alkylamides) and generate potentially carcinogenic compounds called NOCs.
But there’s actually little evidence that NOCs are carcinogenic in humans (Powlson DS et al. 2008).
As the authors of a recent review wrote, “Direct evidence of the participation of nitrate and nitrite in human carcinogenesis is lacking ...” (Hord NG et al. 2009)
And manufacturers who add nitrites to processed meats are required by law to add antioxidants that block the formation of potentially carcinogenic NOCs.
So the links between increasing consumption of processed meats and greater risk of cancer probably relates to other constituents of these products … including red meat itself.
One group received a high-nitrate diet – with the nitrate boost coming from beet juice – while the others ate a low-nitrate diet.
The scientists then measured the extent of cerebral perfusion (blood flow to various parts of the brain) using a special form of magnetic resonance imaging (MRI) scanning.
While the high-nitrate diet did not boost blood flow brain-wide, it lead to increased flow in areas of the frontal lobe white matter where poor blood flow is associated with having dementia.
(Specifically, the high-nitrate group showed increased blood flow in the subcortical and deep white matter, between the dorsolateral prefrontal cortex and anterior cingulate cortex.)
As the authors concluded, “These results suggest that dietary nitrate may be useful in improving regional brain perfusion [blood flow] in older adults in critical brain areas known to be involved in executive functioning.” (Presley TD et al. 2010)
Based on this documented boost to blood flow in relevant parts of the brain, they proposed that dietary nitrates – such as from beets and other nitrate-rich vegetables – could deter, reduce, or delay age-related cognitive decline (ARCD) as well as Alzheimer’s and other disabling dementias.
“Our results support the proposal that oral nitrate therapy may be beneficial in treating [the] cognitive decline that is often observed with aging.” (Presley TD et al. 2010)
His team also noted that the higher blood levels of nitrite and nitrate seen in the high-nitrate group lasted after an overnight fast, suggesting that the beneficial effects of dietary nitrate may persist at least that long.
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