WEDNESDAY, Nov. 21, 2018 (HealthDay News) -- When your mom told you to eat your veggies and drink your orange juice, she was on to something: They may help preserve your brain health, new research suggests.
A 20-year study of men who were health professionals tied a diet rich in leafy greens, orange and red vegetables, berries and orange juice to reduced risk of memory loss (or "cognitive function").
"This study adds to existing research that higher intake of vegetables and fruits in the long term may play an important role in maintaining cognitive function," said lead author Changzheng Yuan. She is a postdoctoral research fellow at Harvard T.H. Chan School of Public Health.
Yuan cautioned that this study cannot prove these nutrient-laden dietary choices reduce memory loss, only that they're related. Also, the results may not apply to women or men outside the health professions.
For the study, which was partly funded by the U.S. National Institutes of Health, the researchers collected data on nearly 28,000 male health professionals, average age 51.
Participants completed questionnaires about how many servings of fruits, vegetables and other foods they ate daily at the study's start and every four years thereafter for 20 years.
Fruits and vegetables contain high levels of antioxidant nutrients, the researchers noted.
A fruit serving is defined as one cup of fruit or one-half cup of fruit juice. A serving of vegetables is one cup of raw vegetables or two cups of leafy greens.
The participants were asked about their thinking and memory skills at least four years before the end of the study, at age 73 on average.
Questions included, "Do you have more trouble than usual remembering a short list of items, such as a shopping list?" and "Do you have more trouble than usual following a TV program due to your memory?"
Changes in memory were considered early signs of mild cognitive impairment.
Overall, 55 percent said that they still had good thinking and memory skills, 38 percent had moderate skills, and 7 percent had poor thinking and memory skills, the findings showed.
How great was the protective effect? Men who ate the most vegetables -- about six servings a day -- were 34 percent less likely to develop poor thinking skills than those who ate the least -- just two servings.
Moreover, daily orange juice drinkers were 47 percent less likely to develop poor thinking skills, compared with men who drank less than one serving a month, the researchers found. This association was seen mostly among the oldest men.
The study showed that less than 7 percent of frequent veggie eaters developed poor memory function, compared with 8 percent of men who avoided their fruits and greens. The results were similar among frequent and infrequent orange juice drinkers.
Since fruit juice is usually high in calories, it's generally best to drink a small glass, 4 to 6 ounces, a day, Yuan said. "Even better is choosing the whole piece of fruit instead, which contains the added benefit of fiber," she suggested.
Although men who ate the most fruit were also less likely to develop memory problems over time, that association weakened when the researchers accounted for consumption of vegetables, fruit juice, refined grains, legumes and dairy products.
Long-term habits also appeared to play a role. Those who ate lots of fruits and veggies 20 years before the memory test were less likely to develop thinking and memory problems, whether or not they did so in the six years before the memory test.
Rebecca Edelmayer is director of scientific engagement at the Alzheimer's Association. She noted that, because this study relies on participants' recall, it is not as rigorous as other studies.
Still, it makes a valid point that preserving mental health is, to some degree, a matter of lifestyle, just like preventing heart disease, she added.
"This is a hot topic of research right now," Edelmayer said.
A healthy diet plus exercise and mental stimulation might reduce your risk for mental decline, she said. "We see a future where Alzheimer's disease will be treated with a medication, but also life intervention -- like we do with heart disease," Edelmayer said.
The report was published online Nov. 21 in Neurology.
For more on keeping your brain healthy, visit the Alzheimer's Association.