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  • High blood levels of antioxidants were linked with a lower risk of dementia.
  • Experts suggest eating foods rich in antioxidants, including dark, leafy greens and orange fruits.
  • Researchers caution that more research is needed before we know how much of these antioxidants have the biggest impact on lowering the risk of dementia.

People with higher levels of certain antioxidants in their blood may be less likely to develop dementia later on, a new study shows.

This adds to growing evidence that eating a wide variety of fruits and vegetables rich in these phytonutrients may have long-term benefits for the brain.

Researchers caution that more research is needed before we know how much and which of these antioxidants have the biggest impact on lowering the risk of dementia.

“This study may indicate that only certain types of carotenoids may be effective at reducing the risk for dementia, and those may include lutein+zeaxanthin and beta-cryptoxanthin,” said study author May Beydoun, PhD, an epidemiologist with the National Institutes of Health’s National Institute on Aging in Baltimore.

However, “without evidence from randomized controlled trials, it is too early to advise people to make changes in their diet,” she added.

Researchers used data on over 7,200 participants from the third National Health and Nutrition Examination Survey (NHANES 1988-1994).

People were 45 to 90 years old at their first study visit and were followed for an average of 16 to 17 years and for up to 26 years.

All participants were free of dementia at the first visit, during which they had an interview, physical exam, and a blood draw to measure antioxidant levels.

Researchers looked to see how many people were diagnosed with dementia during the follow-up period, including Alzheimer’s disease and other types.

People 65 years or older at baseline with the highest blood levels of lutein and zeaxanthin had a lower risk of developing any type of dementia during the follow-up period compared to people with lower levels of those antioxidants.

High levels of beta-cryptoxanthin, compared to lower levels, were linked to a lower risk of any type of dementia in both 45- to 64-year-olds and those 65 years or older at baseline.

These specific antioxidants are a type known as carotenoids, which give fruits and vegetables their yellow, orange, and red color.

Lutein and zeaxanthin are found in high amounts in dark-green vegetables such as kale, spinach, and broccoli. Beta-cryptoxanthin is abundant in fruits such as oranges, papaya, peaches, and tangerines.

The apparent protective effect of these antioxidants was reduced somewhat when researchers considered other factors such as income, education, and physical activity. This suggests that these other factors also shape the risk of developing dementia.

No clear link was seen between dementia risk and lycopene, alpha-carotene, beta-carotene, or vitamins A, C, or E.

The study was published online May 4 in Neurology, the medical journal of the American Academy of Neurology.

Some earlier studies have found a link between higher dietary intake of carotenoids or flavonols and reduced risk of Alzheimer’s dementia. Other studies, though, have been less conclusive.

Flavonols are found in a wide variety of fruits and vegetables, as well as certain teas.

The different results among studies could be due to the way they are carried out, differences in the people included in the study, which types of foods they generally eat, along with several other factors.

In addition, many studies just measure antioxidant levels based on which foods people eat. This requires people to track their diet for a period of time or try to remember what they ate during that time.

In contrast, the current study measured antioxidant levels in the blood sample, which provides a more accurate picture of these nutrients — at least for that moment in time.

One of the study’s limitations is that researchers only assessed antioxidant levels once. Ideally, researchers would monitor people at multiple points in their life to see if there is a shift.

However, Dr. Thomas M. Holland of the Rush Institute for Healthy Aging said, “people’s diets tend to be quite stable over time … unless somebody has a major life event” that spurs them to change their diet.

This event could be as small as their doctor telling them they have high blood pressure or something more serious such as a heart attack or stroke.

In addition to the antioxidant levels in the blood, Beydoun and her colleagues also looked at participants’ diet quality, which was based on their recall of what they ate over a 24-hour period.

Beydoun said they expect diet quality to be directly related to most — but not all — antioxidant levels measured with a blood test.

This is particularly true for carotenoids and vitamin C, she said, as well as when the diet quality index strongly emphasizes intake of fruits and vegetables.

In addition, Beydoun said, “other external factors may influence these [antioxidant] levels, including other lifestyle factors such as smoking tobacco, drinking alcoholic beverages, and consuming a high-fat diet.”

Like much of the previous research, the new study is an observational study, so it can’t prove the connection between antioxidant levels and the risk of dementia.

For that, randomized clinical trials will be needed, such as with a specific diet or antioxidant supplements. Researchers would then follow people over time to see how many participants developed dementia.

Additional studies are also needed to determine how much of which foods people need to consume each day to reach antioxidant levels that promote brain health.

“There is so much still to be understood about how these nutrients are getting into the body and then further, how they’re being utilized,” said Holland, including how the nutrients may support brain health.

While we wait for researchers to answer some of those questions, Holland said studies of specific diets show the benefits of diet for the brain.

He points to the Mediterranean-DASH Intervention for Neurodegenerative Delay” (MIND) diet, which was developed by Rush nutritional epidemiologist Martha Clare Morris, ScD, and colleagues.

This diet is similar to the heavily plant-based Mediterranean diet, with an emphasis on antioxidant-rich berries and green, leafy vegetables.

One randomized controlled trial published this year found that this diet improved mental performance and brain structure in healthy women with obesity.

“[The Neurology] study, as well as these other studies, [found brain-related benefits of consuming] leafy greens, especially the dark leafy greens — kale, arugula, spinach, romaine lettuce,” said Holland.

“Those are nutrient-dense,” he added. “They are, as some would say, power foods that should really be consumed one serving a day.”