A diet rich in the antioxidants that leafy, green vegetables and colorful fruit deliver is good for your body, and now new research shows it also protects your brain.
In the study, people whose blood contained the highest amounts of three key antioxidants were less likely to develop all-cause dementia than those whose blood had lower levels of these nutrients.
"The takeaway is that a healthy diet rich in antioxidants from dark leafy greens and orange-pigmented fruits with or without antioxidant supplements may reduce the risk of developing dementia," said Dr. Luigi Ferrucci, scientific director for the U.S. National Institute on Aging (NIA), which funded the study.
"But the only way to prove the connection between antioxidants and brain health is with a long-term, randomized clinical trial to see whether fewer people who take a carefully controlled amount of antioxidant supplements develop dementia over time," Ferrucci added.
For this new research, study author May Beydoun of the NIA, in Baltimore, and colleagues studied nearly 7,300 people, aged 45 to 90, who had a physical exam, an interview and a blood test for antioxidant levels.
The individuals were divided into three groups, depending on the level of antioxidants in their blood, and followed for an average of 16 years and as many as 26 years.
The researchers found that those who had the highest amount of the antioxidants lutein and zeaxanthin in their blood were less likely to develop dementia than those who had lower levels. Lutein and zeaxanthin are found in green leafy foods like kale, spinach, broccoli and peas.
Every increase in standard deviation (a measure of how dispersed the data is in relation to the average) of those antioxidant levels in the study was associated with a 7% decrease in dementia.
For those who had high levels of another antioxidant called beta-cryptoxanthin, every standard deviation increase was associated with a 14% reduced risk of dementia. Beta-cryptoxanthin is found in orange-pigmented fruits, including oranges, papaya, tangerines and persimmons.
"Experts believe that consuming antioxidants may help protect cells of the body — including brain cells — from damage," Ferrucci said.
The impact of antioxidants on dementia risk was reduced somewhat when researchers also accounted for education, income and physical activity. Those factors may help explain the relationship between antioxidant levels and dementia, the study authors said.
The study also only measured blood at one time and may not reflect participants' antioxidants levels over their lifetimes.
"It is important to keep in mind that experts do not yet know how much antioxidants we need to consume each day through our diet and supplements for a healthy brain," Ferrucci said.
Determining ways to prevent the development of dementia is an important public health challenge, he added, but the results of previous studies have been mixed.
The researchers said that antioxidants may help protect the brain from oxidative stress, which can cause cell damage.
"Population studies that follow healthy people over many years for the development of dementia enable us to look for potential risk factors and also protective factors, such as dietary and lifestyle choices," Ferrucci noted.
The findings were published online May 4 in the journal Neurology.
Yuko Hara, director of Aging and Alzheimer's Prevention at the Alzheimer's Drug Development Foundation, said the study was unique in its use of blood markers rather than patient recall about foods they have eaten.
Hara also noted that the association between the antioxidants and dementia in this study was lessened when accounting for other factors.
"It's not that they're not involved, it's the totality I think, and it's part of the many different things you can do for good brain health," said Hara, who was not involved in this study.
Hara said her organization recommends seven steps for brain health.
These include good nutrition, with an emphasis on following a Mediterranean diet, getting seven to eight hours of a sleep each night, and exercising at moderate intensity for at least 150 minutes per week.
The other steps are easing stress, being social, continuing to learn and managing chronic illnesses that have been associated with dementia risk, including diabetes and high blood pressure (hypertension).
"These are conditions that if you leave it untreated you are also harming your brain health and potentially [increasing] Alzheimer's risk, as well as overall dementia risk. If you have those conditions, you really want to keep them under control with lifestyle interventions or, if not enough with lifestyle interventions, most likely your doctor will prescribe you medications so that your blood pressure and glucose levels will be managed well," Hara said. "That's what we recommend."
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