Effects of blueberry and cranberry consumption on type 2 diabetes glycemic control: A systematic review

ABSTRACT

The metabolic effects of cranberry and blueberry consumption on glycemic control have been evaluated in vitro and in animal models as well as in human studies, although findings have not been systematically reviewed yet. Therefore, a systematic review was carried out of relevant randomized clinical trials (RCTs) in order to assess the effect of berries (blueberry and cranberry) consumption on type 2 diabetes (T2DM) glycemic control. Some evidences were also discussed on the anti-diabetic mechanisms exerted by berries polyphenols. Studies were identified by searching electronic databases: LILACS, PubMed/MEDLINE, Scopus, The Cochrane Library and Web of Science. Three authors independently searched and extracted RCTs in which the effect of berries (cranberry or blueberry) consumption on T2DM glycemic control was assessed. A total of 7 RCTs, involving 270 adults with type 2 diabetes were included. Despite the heterogeneity of the administration forms (in natura, dried, extract, preparations – juice), dosage, duration of the intervention and type of population of the studies involving these two berries some studies highlight the potential benefit of berries, especially of blueberry, on glucose metabolism in T2DM subjects. Daily cranberry juice (240 mL) consumption for 12 weeks and blueberry extract or powder supplementation (9.1 to 9.8 mg of anthocyanins, respectively) for 8 to 12 weeks showed a beneficial effect on glucose control in T2DM subjects. Those results indicate a promising use of these berries in T2DM management; although more studies are required to better understand the mechanisms involved.

KEYWORDS:

• Anthocyanins
• glucose control
• glycemic response
• nutraceuticals
• polyphenols

Conflict of interest

The authors state that they have no conflict of interest.

Acknowledgments

We thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Foundation by grants to Caldas APS, Rocha DMUP and da Silva BP. Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) have supported related research projects. Hermsdorff HHM and Alfenas RCG are CNPq fellows.

Additional information

Funding

Conselho Nacional de Desenvolvimento Científico e Tecnológico, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, e Fundação de Amparo à Pesquisa do Estado de Minas Gerais.