The effects of polyphenol rich chocolate on cardiovascular risk and glycaemic control in type 2 diabetes mellitus

Mellor, Duane Daniel

Abstract

Background:
Type 2 diabetes mellitus (T2DM) is characterised by increased rates of morbidity and mortality, much of which is related to cardiovascular disease. T2DM is considered to be a non-communicable disease, with its cause and aetiology linked to a number of genetic factors, which are influenced by dietary behaviours and lifestyle. Diet has a significant role to play in the prevention and management of T2DM. Both in vitro and in vivo studies suggest that plant flavanols may have beneficial effects for people with diabetes, including potentially those found in cocoa and chocolate. Cesar Fraga suggested in 2005 that perhaps we should eat more chocolate to prevent and manage diabetes, following a study of just 15 healthy individuals, which demonstrated improvements in insulin sensitivity and blood pressure. Despite this remark seven years ago, almost no work has been published outside of that presented in this thesis has investigated the effect of chocolate containing only its native flavanols (predominantly epicatechins) on glycaemic control and markers of cardiovascular risk in T2DM.

Methodology:
An exploratory review of the literature suggested that the effect of chocolate might be greater than that seen with cocoa. This thesis considered the published literature to ascertain whether chocolate provides greater efficacy over cocoa supplementation using a meta-analysis. This led into a series of clinical trials aimed at testing chocolate supplementation at levels which provide an adequate dose of flavanols without leading to excess energy or sugar intake. The first of the three studies consisted of a proof of concept study feeding 45g of chocolate over eight weeks in a double-blinded randomised crossover design (n=12). The second, using 13.5g again used a doubleblinded randomised crossover design to assess the acute effects of flavanols rich chocolate over a three-hour period in individuals with T2DM with an induced transient hyperglycaemia caused by a 75g oral glucose load (n=10). The final clinical trial was a three-arm randomised double-blinded parallel study aimed to investigate the effects over a 12-week period of milk chocolate enriched with flavanols in an attempt to maximise palatability.

Results:
The exploratory review with meta-analysis demonstrated that chocolate supplementation resulted in significantly greater reduction in blood pressure (both systolic and diastolic, sub-group analysis, p<0.05) compared to cocoa supplementation. Cocoa was significantly more effective at reducing LDL cholesterol (p=0.02). The key difference between studies which used chocolate (38.8±13.1%) and those which used cocoa (68.2±13.8%) was the chocolate used in trials appeared to have significantly lower percentage energy from carbohydrate (p<0.001). The pilot study provided 45g of chocolate for 8 weeks, had no adverse effects on weight or glycaemia despite it providing an additional daily energy content of 1.03Mj (246kcal). HDL cholesterol improved following consumption of high flavanols chocolate (p=0.05) with HDL cholesterol: total cholesterol significantly falling (p=0.04). The provision of 13.5g of flavanols rich chocolate prior to a 75g oral glucose load, resulted in improved endothelial function, measured by Reactive Hyperaemia- Peripheral Artery Tonography (RH-PAT) as a functional measure and adhesion molecules (P>0.05). This effect was accompanied by a simultaneous reduction in urinary 15-F2t-isoprostane (a marker of oxidative stress). The final study using a milk chocolate and lower doses of epicatechin did not have an adverse effect on weight or glycaemia after 12 weeks, with participants actually gaining weight in the four weeks immediately after the completion of the study (p=0.002). No clear beneficial effects of any one chocolate were seen.

Conclusion:
The work in this thesis finally provides evidence to support Fraga’s suggestion, that there are benefits in terms of improved lipid profile and endothelial function with chocolate supplementation for individuals with T2DM. The equivocal results from the final study which used a chocolate containing about a third of the epicatechin dose of the first two studies, suggest that the dose required for benefit may be at least that accepted as being beneficial with respect of endothelial function (EFSA, 2012a) at
200mg of flavanols in the general population for individuals with T2DM.

Citation

Mellor, D. D. (2013). The effects of polyphenol rich chocolate on cardiovascular risk and glycaemic control in type 2 diabetes mellitus. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4214543

• Thesis Type: Thesis
• Deposit Date: Oct 2, 2013
• Publicly Available Date: Feb 23, 2023
• Keywords: Medicine
• Public URL: https://hull-repository.worktribe.com/output/4214543
• Additional Information: Postgraduate Medical Institute, The University of Hull
• Award Date: Jan 1, 2013