Patients with type 2 diabetes and poor glycemic control are more likely to have a lower cognitive function; could a Mediterranean diet help protect against cognitive decline?
Previous research has suggested that eating foods like those found in the Mediterranean diet might help to protect against cognitive decline, as well as in preventing and controlling type 2 diabetes.
The Boston Puerto Rican Health Study was a longitudinal observational study conducted on 1,499 Puerto Rican adults, either with or without type 2 diabetes. The study intended to assess the “association of a Mediterranean diet score with a 2-year change in cognitive function by type 2 diabetes and glycemic control status, and to contrast it against other diet quality scores.” The patients underwent a baseline visit and a follow-up visit at 2 and 5 years. After a fast, serum glucose was measured and HbA1C was analyzed. A fasting plasma glucose > 126 mg/dL defined type 2 diabetes or the use of diabetes medication. Those with an A1C > 7% were considered uncontrolled, and controlled was an A1C < 7%. To assess values after the two years, a reduction of < 0.5% was considered stable or improved and those with an increase in > 0.5% were considered poor or declined values. One thousand two hundred forty-six patients completed the two-year visit. The primary outcome assessed was change in global cognitive function.
Seven neuropsychological tests were performed on each patient, including Mini-Mental State Examination (MMSE), word list learning, word list recognition, percent retention Stroop, letter fluency, digit span forward, digit span backward, clock drawing, and weighted figure copying. By averaging the z scores from the tests, a global cognitive function score was calculated. Using a principal component analysis, cognitive function factors were derived, and two factors recognized and considered as “executive” and “memory” functions. Lastly, covariates were asked and recorded by trained research interviewers.
Each diet had to be assessed before comparison. To determine the traditional foods of the Puerto Rican population that adhered to a Mediterranean diet, a food frequency questionnaire was used, giving nine dietary components. Points were assigned to individuals, then summed, with a range from 0 to 9, low adherence to high adherence. Next, the Healthy Eating Index included 12 food and nutrient components, summed to a range of 0 to 100; the higher the number indicated better adherence. The next diet studied was the Alternate Healthy Eating Index, including 11 food groups or nutrient components, each given a continuous score between 0 and 10, 0 for the minimal observance and 10 for the maximal observance. The range was from 0 to 110, with the lowest diet quality to the highest diet quality. Lastly, Dietary Approaches to Stop Hypertension diet was assessed, ranging from 8 to 40.
Different analyses were used based on the variables; Student t-test or ANOVA were used for continuous variables or X2 for categorical. To assess the 2-year change in global cognitive function z score, executive and memory function composite scores, and individual cognitive test scores, repeated-measures linear mixed-effects models were used. To evaluate the change in outcomes by baseline dietary score, models were adjusted for all covariates. All models were stratified by type 2 diabetes status and glycemic control status.
Comparing patients with type 2 diabetes, at baseline, there were 39.5% and at two years, 42.6%. Furthermore, of those patients, at baseline, 74.2% were not under glycemic control and at two years, 67.9% experienced poor or a declined HbA1C. Comparing the two groups at baseline, those with type 2 diabetes had higher mean age, lower educational achievement and physical activity score, higher incidence of hypertension, body mass index, C-reactive protein, glucose, and HbA1C. Of the patients with type 2 diabetes, comparing uncontrolled versus controlled at baseline, those with uncontrolled glycemic levels had higher C-reactive protein, glucose and HbA1C and at two years, lower executive memory function.
After adjustment for covariates, the Mediterranean diet score was associated with a positive 2-year change in memory function (P = 0.016) in patients without type 2 diabetes, but none of the other cognitive scores. In the fully adjusted model, the diet explained 0.5% of the variability and age explained 0.6%. In patients with type 2 diabetes, after adjusting for baseline score, a higher Mediterranean diet score was associated with higher 2-year change in score of global cognitive function, MMSE, word recognition, digit span forward, and clock drawing (P values listed respectively, 0.016, 0.031, 0.017, 0.023, 0.022). The age at baseline accounted for 0.22% of variability in the model, and the diet accounted for 1.4%.
Adjusting for age and sex, crude models showed similar results as the fully adjusted model. Not only was an association between the Mediterranean diet score and 2-year change in memory function seen, but a significant association in word list learning and figure copying (P = 0.032, P = 0.022). In patients with type 2 diabetes, the crude models didn’t show a significant 2-year change in word recognition (P = 0.09). While adhering to the Mediterranean diet showed positive results in patients with type 2 diabetes, the other diets tested were not significantly associated with cognitive function, whereas there was an association with better memory function from all the diets tested in patients without type 2 diabetes. The authors noted, in patients with type 2 diabetes, a significant association was observed in those under glycemic control at baseline and who over the two years remained stable or improved glycemic control.
The authors concluded when patients with type 2 diabetes adhere to a Mediterranean diet, there is an association with a higher 2-year cognitive function. This association had further benefit with proper glycemic control. Additionally, this study specifically shows the benefits towards cognition by adhering to a Mediterranean diet in both patients with and without type 2 diabetes. It is important for dietary recommendations to be individualized for each patient and to help pick appropriate foods that patient enjoys. This study explicitly focused on the Puerto Rican population, which the authors acknowledged might limit the possibility for generalizability, but dietary choices can be made based off each population or culture, and still promote a healthy Mediterranean diet.
- A healthy diet focused around the Mediterranean diet has shown an association with a higher 2-year cognitive function.
- Patient diets should be individualized, finding similar foods to the Mediterranean diet they are willing to eat, for best potential of adherence.
- Along with promoting a healthy Mediterranean diet in patients with type 2 diabetes, proper glycemic control showed additional benefit in a higher 2-year cognitive function.
Reference for “Diet Changes to Protect Against Cognitive Decline in Patients with Type 2 Diabetes”:
Mattei, Josiemer, et al. The Mediterranean Diet and 2-Year Change in Cognitive Function by Status of Type 2 Diabetes and Glycemic Control. Diabetes Care. 2019 May
Emma Kammerer, L|E|C|O|M Bradenton School of Pharmacy, PharmD Candidate