Over the years, I have reported on several studies that have found evidence that colorful berries — blueberries in particular (but I think that’s more of an artifact, due to the relative cheapness of these berries in North America) — benefit older brains. Indeed, I myself consume these every day (in my lunch smoothie) for this very reason (of course, the fact that they taste so good doesn’t hurt!).

But to date these studies have involved rodents or only very small numbers of humans. Now a new study analyzes data from the very large and long-running Nurses' Health Study, which has questioned 121,700 female, registered nurses about their health and lifestyle since 1976. Since 1980, participants were also asked about their frequency of food consumption. Between 1995 and 2001, memory was measured in 16,010 participants over the age of 70 years (average age 74), at 2-year intervals.

The study found that those women who had 2 or more servings of strawberries and blueberries every week had a slower rate of cognitive decline. The effects were equivalent to some 1.5-2.5 years of normal cognitive aging.

While the researchers cannot completely rule out the possibility that higher berry consumption is associated with slower cognitive decline because of its association with some other factor that affects brain aging, they did take into account a large number of potentially confounding factors, including: education, smoking history and status, antidepressant use, BMI, blood pressure, cholesterol, diabetes, physical activity, total calorie intake, fish consumption, alcohol use, overall diet scores, and various indirect measures of socioeconomic status.

Moreover, the findings are both consistent with both animal and cell studies, and with what we know about how the brain ages. The ‘magic’ ingredient of these berries is thought to lie in their flavonoids (particularly anthocyanidins), which have powerful antioxidant and anti-inflammatory properties. It’s thought that berries help the brain stay healthy both because they contain high levels of antioxidants, which protect cells from damage by harmful free radicals, and because they change the way neurons in the brain communicate, protecting against inflammation and oxidative stress.

As a rule of thumb, the deeper the color of the berry (or other fruit or vegetable), the more flavonoids it has. You can see a list of anthocyanin-rich foods here (acai isn’t in the list, but it also has a very high rating).