Berries, apples, tea potential protective benefits against Alzheimer's

Older adults who consumed small amounts of flavonoid-rich foods, such as berries, apples and tea, were two to four times more likely to develop Alzheimer's disease and related dementias over 20 years compared with people whose intake was higher, according to a new study led by scientists at the Jean Mayer Human Nutrition Research Center on Aging at Tufts University in Boston, Massachusetts. The research was published in the journal the American Journal of Clinical Nutrition.

The epidemiological study of 2,800 people aged 50 and older examined the long-term relationship between eating foods containing flavonoids and risk of Alzheimer's disease and Alzheimer's disease and related dementias. While many studies have looked at associations between nutrition and dementias over short periods of time, the study looked at exposure over 20 years.

The researchers analyzed six types of flavonoids and compared long-term intake levels with the number of AD and ADRD diagnoses later in life. They found that low intake of three flavonoid types was linked to higher risk of dementia when compared to the highest.

To measure long-term flavonoid intake, the research team used dietary questionnaires, filled out at medical exams approximately every four years by participants in the Framingham Heart Study, a largely Caucasian group of people who have been studied over several generations for risk factors of heart disease.

To increase the likelihood that dietary information was accurate, the researchers excluded questionnaires from the years leading up to the dementia diagnosis, based on the assumption that, as cognitive status declined, dietary behavior may have changed, and food questionnaires were more likely to be inaccurate.

The participants were from the Offspring Cohort, children of the original participants, and the data came from exams 5 through 9. At the start of the study, the participants were free of Alzheimer's disease and Alzheimer's disease and related dementias, with a valid food frequency questionnaire at baseline. Flavonoid intakes were updated at each exam to represent cumulative average intake across the five exam cycles.

Researchers categorized flavonoids into six types and created four intake levels based on percentiles, less than or equal to the 15th percentile, 15th-30th percentile, 30th-60th percentile, and greater than 60th percentile. They then compared flavonoid intake types and levels with new diagnoses of Alzheimer's disease and Alzheimer's disease and related dementias.

Flavonoids are natural substances found in plants, including fruits and vegetables such as pears, apples, berries, onions, and plant-based beverages like tea and wine. Flavonoids are associated with various health benefits, including reduced inflammation. Dark chocolate is another source of flavonoids.

The research team determined that low intake of three flavonoid types was linked to higher risk of dementia when compared to the highest intake. Specifically, low intake of flavonols in apples, pears, and tea was associated with twice the risk of developing Alzheimer's disease and related dementias; low intake of anthocyanins in blueberries, strawberries, and red wine was associated with a four-fold risk of developing Alzheimer's disease and related dementias; and low intake of flavonoid polymers in apples, pears, and tea was associated with twice the risk of developing Alzheimer's disease and related dementias, according to the study.

The results were similar for Alzheimer’s disease, the researchers said.

There are some limitations to the study, including the use of self-reported food data from food frequency questionnaires, which are subject to errors in recall. The findings are generalizable to middle-aged or older adults of European descent. Factors such as education level, smoking status, physical activity, body mass index, and overall quality of the participants' diets may have influenced the results, but researchers said they accounted for those factors in the statistical analysis. Due to its observational design, the study does not reflect a causal relationship between flavonoid intake and the development of Alzheimer's disease and Alzheimer's disease and related dementias, the researchers said.