Metabolic Benefits of Drinking Blueberry Tea in Type 2 Diabetes

Plant derived compounds, e.g. flavonoids from dark chocolate, green tea, or blueberries, show great potential as nutraceuticals for the treatment of various diseases such as type 2 diabetes (T2D). Flavonoids have been suggested to improve glucose metabolism, reduce blood lipids, reduce oxidative stress and improve vascular function. For these reasons we recently investigated the effects of daily consumption of locally produced blueberry tea and demonstrated that this could partially restore insulin sensitivity in an animal model. We propose to translate these findings to assess the efficacy of this nutraceutical as a new treatment for improving glucose tolerance in people with T2D.

Current treatments for T2D are limited, have unwanted side effects, and lose effectiveness over time. There is a growing public interest in the use of complementary and alternative approaches for treating insulin resistance and T2D. Blueberries, blueberry leaves and cinnamon have each been reported to improve insulin sensitivity or insulin action. Blueberry Boost™ is a locally produced Blueberry Tea and is a proprietary blend of dried blueberries (37% wt/wt), blueberry leaves, raspberry leaves, spearmint leaves and cinnamon. It is well established that improving glycemic control is important for managing insulin resistance and T2D and the associated vascular pathologies that directly contribute to end-organ damage (microvascular disease), hypertension and cardiovascular disease (stroke, heart attack and heart failure). We have recently demonstrated that a unique blueberry tea blend fully restores the vascular insulin sensitivity in muscle of the high-fat fed insulin-resistant rat model and is associated with substantial improvements in muscle glucose uptake and whole body insulin sensitivity. We propose to translate these findings to assess the efficacy of this nutraceutical as a new treatment for improving glucose tolerance in people with T2D. Aim: Determine whether chronic consumption (4 weeks) of blueberry tea can improve metabolic and vascular health in people with and without T2D.

Oral glucose tolerance test (75g glucose) measured on 3 occasions: at baseline, after 4 weeks of drinking blueberry tea, and after 4 weeks of no treatment (randomized cross-over design). Blood glucose and plasma insulin levels measured at 0, 15, 30, 60, 90 and 120 min following consumption of glucose load.

HbA1c levels measured on 3 occasions: at baseline, after 4 weeks of drinking blueberry tea, and after 4 weeks of no treatment (randomized cross-over design).

Improvement in fasting Serum Lipid (cholesterol, HDL, LDL,triglycerides) levels after 4 weeks of drinking blueberry tea.

Fasting serum lipids (cholesterol, HDL, LDL,triglycerides) measured on 3 occasions: at baseline, after 4 weeks of drinking blueberry tea, and after 4 weeks of no treatment (randomized cross-over design).

Improvement in fasting serum pro-inflammatory cytokine (IL-6, IL-1b, CRP, TNFa) levels after 4 weeks of drinking blueberry tea.

Fasting serum pro-inflammatory cytokines (IL-6, IL-1b, CRP, TNFa) assessed by ELISA will be measured on 3 occasions: at baseline, after 4 weeks of drinking blueberry tea, and after 4 weeks of no treatment (randomized cross-over design).

Fasting serum albumin levels measured on 3 occasions: at baseline, after 4 weeks of drinking blueberry tea, and after 4 weeks of no treatment (randomized cross-over design).

Fasting serum electrolytes (Na, K, Cl, HCO3) measured on 3 occasions: at baseline, after 4 weeks of drinking blueberry tea, and after 4 weeks of no treatment (randomized cross-over design).

Improvement in Resting Blood Pressure (central and brachial blood pressure) after 4 weeks of drinking blueberry tea.

Blood Pressure (central and brachial blood pressure) will be measured by Mobil-O-Graph and assessed on 3 occasions: at baseline, after 4 weeks of drinking blueberry tea, and after 4 weeks of no treatment (randomized cross-over design).

Augmentation index will be measured by Mobil-O-Graph and assessed on 3 occasions: at baseline, after 4 weeks of drinking blueberry tea, and after 4 weeks of no treatment (randomized cross-over design).

Large artery stiffness will be measured by Mobil-O-Graph and assessed on 3 occasions: at baseline, after 4 weeks of drinking blueberry tea, and after 4 weeks of no treatment (randomized cross-over design).

Inclusion Criteria: Aged 18-75 years. Normal to overweight (BMI 19-35 kg/m2). On lifestyle or metformin only diabetes treatment. Normotensive (seated brachial blood pressure <160/100 mmHg). No history of T2D (e.g. fasting plasma glucose <7.0mM); or with clinically diagnosed T2D on metformin or lifestyle intervention only (e.g. fasting plasma glucose ≥7.0mM, HbA1c). Willing to drink blueberry tea for 4 weeks (3 times per day with meals). Exclusion Criteria: Age <18 yrs or >76 yrs Morbidly obese with a BMI ≥36 kg/m2 Not on lifestyle and/or metformin only treatment for diabetes (e.g. insulin injections, sulphonylureas). History of myocardial infarction or stroke History of malignancy within past 5 years (except for non-melanoma skin cancers) Current smoker History of severe liver disease History of drug or alcohol abuse Elective major surgery during the course of the study Pregnancy/lactation Currently consuming (or have regularly consumed in the past 2 months) blueberry tea, or supplements containing blueberries, blueberry leaves, raspberry leaves, spearmint or cinnamon. Participation or intention to participate in another clinical research study during the study period. Not willing to consume blueberry tea for 4 weeks.

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