May 1, 2012 — Increased consumption of blueberries and strawberries appears to slow cognitive decline in older women, according to an analysis of data from the Nurses’ Health Study (NHS).
“Increasing berry intake appears to slow memory decline by up to 2.5 years,” lead author, Elizabeth E. Devore, ScD, from the Channing Laboratory, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, told Medscape Medical News. “By this, we mean that women eating the most berries vs. little to no berries had memory differences equivalent to women 2.5 years apart in age.”
The news study was published online April 25 in the Annals of Neurology.
Berries and Flavonoids
In their prospective, observational study, which was funded by the National Cancer Institute and the California Strawberry Commission, Dr. Devore and her team evaluated long-term intake of berries and flavonoids in relation to memory decline in 16,010 older women who were participants in the NHS.
The NHS encompasses a large population cohort of 121,700 female registered nurses aged 30 to 55 years who completed health and lifestyle questionnaires starting in 1976.
Between 1995 and 2001, cognitive function was measured every 2 years in study participants aged 70 and older. The mean age of the women in the current analysis was 74, and their mean body mass index was 26 kg/m2.
“Experimental data show that berry supplementation enhances neuronal function and survival and ameliorates age-related cognitive impairment in rodents,” Dr. Devore noted.
Berries are particularly high in a subclass of flavonoids called anthocyanidins, which can cross the blood-brain barrier and localize in the hippocampus, known to be an area of the brain involved in learning and memory, she said.
“Flavonoids have powerful antioxidant and anti-inflammatory properties, and both oxidative stress and inflammation are thought to be important contributors to cognitive impairment. So increased flavonoid consumption could be a potential strategy for reducing cognitive decline in older adults,” she said.
The researchers found that greater intakes of blueberries and strawberries were associated with slower rates of cognitive decline.
After adjustment for age and education, greater consumption of blueberries was highly associated with slower decline in the global score (P trend = .010), the verbal score (P trend = .016), and the Telephone Interview of Cognitive Status (P trend = .027).
The mean difference in rate of global decline was 0.04 standard unit over the study period (95% confidence interval [CI], 0.01 – 0.07) in women who had 1 or more servings of blueberries per week vs those who ate less than 1 serving per week.
They also found that a greater intake of strawberries was related to slower decline in the global and verbal scores after adjustment for age (P trend for global score = .021) and education (P trend for verbal score = .014).
Women who ate 2 or more servings of strawberries per week had an average decline in the global score that was 0.03 standard unit less over the study follow-up period compared with women who had less than 1 serving per week (95% CI, 0.00 – 0.06).
Overall in the study population, the researchers found that 1 year of age was associated with a mean decline of 0.02 standard unit on the global score over the follow-up period.
“Thus, the mean differences that we observed comparing extreme categories of blueberry and strawberry intakes were equivalent to approximately 1.5 to 2.5 years of cognitive aging,” Dr. Devore explained. “Women with higher berry intake appeared to have delayed their cognitive aging by up to 2.5 years.”
However, she cautioned that although the study controlled for other health factors, the possibility that the preserved cognition in those who ate more berries may be also influenced by other lifestyle choices, such as exercising more, cannot be ruled out.
The study does, however, have strengths, she said. “It is the first large epidemiologic study of long-term berry and flavonoid intake in relation to memory decline, utilizing information from over 16,000 older women. In addition, we collected information on berry intake over 20 years prior to initial memory testing, which enabled us to analyze long-term patterns of berry intake.”
For now, however, doctors can tell their patients that eating berries may delay memory decline. “Specifically, eating 1 or more servings per week of blueberries or 2 or more servings per week of strawberries appears to be associated with memory benefits,” Dr. Devore said.
Commenting on this study for Medscape Medical News, David Knopman, MD, from the Mayo Clinic, Rochester, Minnesota, and a spokesperson for the American Academy of Neurology, agreed that the study did have its strengths, including the fact that mid-life dietary practices were assessed at the time, not retrospectively, and its inclusion of a very large number of women who had had 3 cognitive assessments.
However, he said he still has concerns about the study.
“The concerns that I have about the report stem primarily from the fact that studies of associations between dietary habits and health outcomes are notoriously difficult to replicate,” Dr. Knopman said. “Second, the possibility of residual confounding by general health behavior, levels of physical activity, socioeconomic status is a possibility that cannot be discounted. The authors acknowledge this.
I would note that inclusion of physical activity and household annual income in the statistical models that they used attenuated the associations to the point that they were no longer significant.
“Further, I would note that inclusion of physical activity and household annual income in the statistical models that they used attenuated the associations to the point that they were no long significant at the p < 0.05 level for 2 of 3 of the cognitive outcomes,” he said.
“The authors presented the results but did not comment on these analyses in the text of their article or in the abstract. I think that the authors should have said: ‘When controlling for other health-related variables, the associations were attenuated and raise questions about the specificity of our findings.’ Therefore, I remain skeptical that these results reflect what the authors say they do,” Dr. Knopman said.
The study was funded by the National Cancer Institute and the California Strawberry Commission. Dr. Devore and Dr. Knopman have disclosed no relevant financial relationships.