| Date: 08-14-2015 | HC# 021554-526 |
Re: Turmeric Improves Postprandial Working Memory in Patients with Prediabetes
Lee M-S, Wahlqvist ML, Chou Y-C, et al. Turmeric improves post-prandial working memory in pre-diabetes independent of insulin. Asia Pac J Clin Nutr. 2014;23(4):581-591.
People with diabetes or prediabetes have an increased risk for cognitive impairment and dementia. Evidence from epidemiological and experimental studies indicates that turmeric (Curcuma longa, Zingiberaceae) rhizome and cinnamon (Cinnamomum spp., Lauraceae) bark have neuroprotective properties and may help prevent the onset of type 2 diabetes mellitus (T2DM). The authors hypothesize that in people with prediabetes, a refined carbohydrate meal might impair cognitive function, and that working memory (WM; a measure of cognitive function) may improve with adjuvant turmeric or cinnamon supplementation. They also hypothesize that biomarkers of neurodegeneration may vary with WM, and monitoring the biomarkers could help elucidate the mechanism by which turmeric or cinnamon affects WM. These hypotheses were tested in a randomized, placebo-controlled, double-blind study in patients with newly diagnosed prediabetes.
Patients (n=48, aged ≥ 60 years) with newly diagnosed, untreated prediabetes were recruited from a health check-up program at Tri-Service General Hospital, National Defense Medical Center; Taipei, Taiwan. Included patients had a body mass index (BMI) of 18.5-30 kg/m2 (were not obese), fasting glucose between 100-125 mg/dL, no history of medication usage for diabetes, no severe chronic disease, no recent acute illness, and no hospitalization(s) in the preceding 2 months. Excluded patients had a history of heavy drinking in the previous 2 weeks, supplemented their diet with ginseng (Panax spp., Araliaceae) or garlic (Allium sativum, Amaryllidaceae), had a glomerular filtration rate ≥ 45, or had been exposed to a contrast medium within 3 days of the study date.
Patients arrived fasted on the morning of the study. At baseline, a mini-mental state examination (MMSE) and a modification of the n, n-1, n-2 back WM test with n=10 digits were conducted. Weight, height, abdominal circumference, blood pressure, and blood glucose were measured. Also, a semiquantitative food frequency questionnaire (S-QFFQ) was completed to evaluate the use of culinary herbs and spices. Next, each patient ate a standard breakfast of 2 slices of white bread and water, and was given opaque capsules containing either placebo (corn [Zea mays, Poaceae] starch), 2 g Saigon cinnamon (Cinnamomum loureirii) bark (Kirkland Ground Saigon Cinnamon; Costco Wholesale Corporation; Seattle, Washington), 1 g turmeric (a Taiwanese cultivar supplied by Dr. Mei-Shang Ho of Academia Sinica; Taipei, Taiwan), or 2 g cinnamon plus 1 g turmeric. Blood glucose was monitored 2, 4, and 6 hours after breakfast. The WM test was repeated at 6 hours. The blood drawn every 2 hours was also used to monitor plasma insulin and messenger RNA (mRNA) expression of the biomarkers amyloid precursor protein (APP), γ-secretase subunits presenilin-1 (PS1) and presenilin-2 (PS2), and glycogen synthase kinase-3beta (GSK-3β) in peripheral blood mononuclear cells. These biomarkers are thought to reflect amyloid plaque formation and neurofibrillary tangle formation (physiological characteristics of Alzheimer's disease [AD]).
All 4 groups had a similar gender ratio, education level, mean BMI, baseline MMSE score, and WM score. The patients ate a typical Chinese diet, with 80% eating turmeric-containing curry sometimes and 16% consuming cinnamon. Three patients were excluded after randomization; 1 in the cinnamon group for protocol violation and 1 each in the placebo and turmeric-plus-cinnamon groups due to grossly abnormal findings on the study day.
Neither turmeric nor cinnamon altered the glycemic and insulin responses to the breakfast. Turmeric, but not cinnamon, increased WM (P<0.05). It should be noted that since there was no significant difference between the effect of turmeric and the effect of the combination (turmeric and cinnamon) on WM, the authors pooled the data into 2 groups — turmeric users (turmeric group plus combination group, n=23) and non-users (placebo group plus cinnamon group, n=22). Only the pooled data for the change in WM of turmeric users versus non-users is reported.
Multivariate linear regression models were used to evaluate the influence of BMI, glycemia, insulin, and AD biomarkers on WM changes. There were significant negative correlations between insulin response and insulin:glucose ratio versus the improvement in WM. AD biomarker levels were not correlated with improvement in WM. The improvement in WM observed with turmeric was correlated with insulin resistance and BMI.
In summary, turmeric improved postprandial WM in patients with prediabetes. "The extent to which turmeric improved WM was dependent on the participants' body fatness and insulin resistance, suggesting that the benefits of turmeric might be enhanced where these characteristics were less abnormal." The improvement in WM after turmeric ingestion was not related to the amelioration of amyloid plaque (APP, PS1, and PS2 biomarkers) or neurofibrillary tangle formation (GSK-3β biomarker). The authors acknowledge that these findings may not be generalizable since the study included only older people of Chinese ancestry and culture who may have different gut microflora than other populations.
The authors conclude that "co-ingestion of turmeric with white bread increases working memory independent of body fatness, glycaemia, insulin, or AD biomarkers." They suggest these results may also be relevant to the longer-term prevention of diabetes and cognitive impairment. The study was limited by the small sample size and the pooling of data to increase statistical power; the findings should be confirmed in larger and more culturally diverse study populations.
—Heather S. Oliff, PhD
