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.
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.
from the above mechanism, chronic
inflammation has also been associated with the development of insulin
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.
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.
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.
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.
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.
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.
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
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
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.
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.
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
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