Anti-oxidants in Coffee Reduce Blood Sugar but Not Inflammation in Diabetes
A new study published in Nutrition Journal reveals that drinking coffee moderately may reduce blood sugar levels in type-2 diabetics but its antioxidants do not reduce inflammation. This goes to show that coffee's ability to reduce blood sugar levels is not related to its antioxidant properties. On the other hand, tea reduces inflammation but does not affect blood sugar levels in diabetics.
The rising incidence of Type-2 Diabetes Mellitus in Asian countries is having an impact on the quality of life of people. Food and lifestyle play a very important role in the quality of life in diabetics. Therefore, various foods and strategies to improve insulin sensitivity are being studied intensively.
Insulin carries nutrients into tissues, primarily adipose, liver, and muscle tissue. It is released by the beta cells of pancreas in response to an increase in glucose, amino acids, and free fatty acids. Most diabetics suffer from Type-2 diabetes which is characterized by either a decreased ability to secrete insulin or a decrease in insulin sensitivity.
The blood sugar levels rise on food consumption. This triggers the release of insulin so that the glucose can be utilized by the body cells to produce energy. Due to cells being insensitive to the presence of insulin it makes it difficult for the body to remove sugar from the blood leading to type-2 diabetes. Insulin resistance develops when excessive simple sugars are consumed on a daily basis and the insulin levels are high persistently. When insulin secretion is high, the insulin receptors (which bind the glucose insulin complex and carry it into the cell) fall short. A constant demand for excess insulin secretion may also damage the beta cells of the pancreas. This disturbance in the body hormones leads to the development of Type-2 diabetes, insulin resistance and metabolic syndrome.
Apart from the above mechanism, chronic inflammation has also been associated with the development of insulin resistance.
C - reactive protein is a sensitive marker of inflammation. Adiponectin is a protein produced by the adipocytes (fat cells). Higher C-reactive protein (CRP) and lower adiponectin concentrations are known to be associated with insulin resistance.
Coffee is a rich source of antioxidants and has proven to promote insulin sensitivity. In sync with the previous studies, it is postulated that the effect of coffee on lowering CRP (C-reactive protein) concentrations and raising adiponectin concentrations is the possible reason behind improving insulin sensitivity and diabetes overall.
Therefore, Salome A Rebello and colleagues from National University of Singapore conducted a study to analyze the mechanism behind lowering of insulin resistance by coffee and tea intake. They hypothesized that coffee and tea consumption are associated with lower insulin resistance and that this association is due to its effects on lowering inflammation. (As evident by plasma adiponectin and CRP concentrations) The study was conducted in a multi-ethnic population consisting of Chinese, Malays and Asian- Indians.
Data on coffee intake were obtained by asking participants about the habitual amount of coffee consumed. Participants could select one of seven responses ranging from 'never/rarely' to '10 or more cups per day', with 1 cup being defined as a 215 ml standard coffee-shop cup. Similar questions were asked about green tea, Oolong tea and black tea.
Coffee intake was grouped into four categories (never/rarely, less than 1 cup/day, 1-2 cups/day and greater than or equal to 3 cups per day) and tea intake was divided into 3 categories (less than 1 cup/week, 2-6 cups/week, greater than or equal to 1 cup per day) for data analyses.
The investigators found that in a multi-ethnic Singaporean population, coffee consumption was inversely associated with insulin resistance independent of plasma CRP or adiponectin concentrations. This association appeared to be consistent for overweight and non-overweight participants and for Chinese, Malay, and Asian Indian participants. But the results for tea were exactly the opposite.
The authors stated 'We also noted an inverse relationship between green tea and plasma CRP concentrations, but found no evidence for an association between tea consumption and basal glucose metabolism'.
The reason for this beneficial effect has been a decrease in CRP concentrations and an increase in adiponectin levels.
These results suggest that the putative protective effect of coffee consumption against the development of type-2 diabetes is at least partly mediated by its effects on insulin resistance. However, this inverse association between coffee consumption and insulin resistance is probably not mediated by anti-inflammatory effects.
The researchers speculated -
• Although CRP is a well-established marker of systemic inflammation, it is possible that coffee alters other measures of inflammation that were not examined in this study.
• Second, the relatively low amounts of coffee consumed in this population, may have been insufficient to exert a biological effect on CRP and adiponectin.
• Apart from the anti-inflammatory effects, phenolic compounds in coffee have been postulated to affect glucose metabolism.
There was no significant association found between tea consumption and metabolic markers. However, these studies were all clinical trials that examined either the acute or short-term (4-8 weeks) effects of green tea intake. A longer duration may be needed to study the beneficial effects of green tea on CRP.
In conclusion, the researchers suggest that coffee consumption at modest level have beneficial effects on insulin sensitivity in Asians. This association did not appear to be mediated by anti-inflammatory mechanisms, and other pathways need to be considered for mechanistic studies.
Treatments aiming at improving insulin resistance, either non-pharmacological such as foods, or pharmacological such as metformin and thiazolidinediones, may lower CRP levels and thus provide additional therapeutic benefits beyond mere glucose lowering. Prospective studies are clearly needed to address the impact on coffee consumption lowering inflammation.
1. Salome A Rebello et al. "Coffee and tea consumption in relation to inflammation and basal glucose metabolism in a multi-ethnic Asian population: a cross-sectional study" BMC Nutrition Journal;2011
2. Festa et al. "Chronic Subclinical Inflammation as Part of the Insulin Resistance Syndrome" Circiulation; 2000;102:42