Here's some sweet health news for chocolate lovers: A daily dose of the sugary treat may help prevent Alzheimer's disease. That's the conclusion of new research at Harvard Medical School that found people who drank two cups of hot cocoa a day had improved memory and blood flow to the brain.

But the benefits only come from certain types of chocolate, which contain high levels of beneficial antioxidants, notes one of the nation's top Alzheimer's experts, Dr. Gary Small, professor of psychiatry and aging. It's also important to know that you can get too much of a good thing.

"I think it is healthy in moderation, that's the key because if you drink too much cocoa or eat too many chocolate bars you’re going to gain a lot of calories and that is not good for the brain," Dr. Small tells Newsmax Health. "In fact it's the dark chocolates that are particularly potent; milk chocolates have very little and white chocolate has almost none. So if you want the antioxidant boost, go for the dark chocolate."

Scientific research has found dark chocolates — and a host of other foods — contain powerful antioxidant flavonoids that are good for the brain, explains Dr. Small, director of the University of California-Los Angeles Longevity Center.

"As the brain ages, it undergoes wear and tear in what's called oxidative stress," he notes. "And these antioxidants in our foods actually protect the brain from that kind of aging wear and tear."

The latest Harvard study, published in a recent issue of the journal Neurology, found cocoa consumption boosts thinking and memory performance, as well as something called "neurovascular coupling" — where blood flow in the brain changes in response to brain activity — which plays a key role in Alzheimer’s and other mental-health conditions.

For the study, investigators recruited 60 seniors and asked them to drink two cups of hot cocoa a day for a month. Half drank cocoa high in antioxidants, while the others drank cocoa that had lower levels of the beneficial compounds.

At the end of the study, the team tested the participants' memory and thinking skills, and used ultrasound to measure neurovascular coupling in their brains as they completed mental tests. The results showed 18 of the 60 participants had impaired neurovascular coupling problems at the start of the study, but after drinking the high-potency coco, it had improved by 8.3 percent. They also scored better on memory tests.

Dr. Small notes that chocolate isn't the only source of antioxidants. Many vegetables and fruits — including strawberries, blueberries, broccoli, spinach, and other green leafy vegetables — are packed with the beneficial compounds.

"So there are many ways to get antioxidants in your diet and it’s a great idea to get more and more servings of fruits and vegetables," he says. "Most Americans don’t get enough."

At the same time, he also recommends cutting down on foods that have been shown to contribute to mental declines, including milk and dairy products, processed foods, and snacks loaded with refined sugar — such as chips, crackers, and pastries.

"It's okay to have them a little bit, but when we overdo it it's certainly not good for our brains and it's not good for our bodies," Dr. Small says.