The effect of cold exposure on the glycaemic and insulinaemic responses to an oral glucose load

The purpose of the study is to evaluate the effect of cold exposure on an
individual's glucose tolerance. Previous research has already shown that 10
days acclimation to a mild cold environment (14-15°C) can enhance insulin
sensitivity. However, the duration in the cold environment was 6 hours per day
which may not be practical for everyone. Therefore, the present study will
investigate the effect of a shorter, and more intense cold exposure on an
individual's glucose tolerance. It is hypothesised that cold exposure before
consuming a glucose drink will enhance glucose clearance.

Primary objectives:
1) To investigate the effect of cold exposure on the glycaemic and insulinaemic
responses to an oral glucose load in healthy male adults.
2) To investigate the effect of cold exposure on the glycaemic and insulinaemic
responses to an oral glucose load in adults with prediabetes.

Exploratory Objective(s):
To investigate the effect of cold exposure on additional parameters linked to
energy metabolism and thermoregulation.

Sixteen healthy adult males will be recruited for a cross-over design study,
consisting of one screening, two test days and two short visits before the test
days. The participants will be exposed to two thermal conditions on two test
days. The first test day will always be cold exposure and then the second test
day will be exposure to a thermoneutral temperature (serving as the control).
The temperature intervention will be followed by a 1.5 h rest and then an oral
glucose tolerance test (OGTT). Immediately before and 3 h following the intake
of the glucose drink, blood sampling will be performed to monitor glucose and
insulin concentrations. Between each test day there will be at least 10 days to
prevent the previous test effecting the next test.
Depending on the outcome of the study in healthy adult males, the study may be
repeated with 16 adults with prediabetes as the target population. If the cold
exposure is accepted by the healthy population it would be important to then
test the cold exposure in a population with disturbed glucose metabolism, with
the aim to investigate if the cold exposure can improve hyperglycaemia.

Participants will be wrapped in a water-perfused suit. The temperature of the
suit will be lowered to 10°C. From the onset of shivering, the participants
will remain in the suit for 1 hour.

For the control:
Participants will be wrapped in a water-perfused suit. The temperature of the
suit will remain at a thermoneutral temperature (32°C) to avoid shivering and
excessive sweating. The duration will be matched to that of the cold exposure.

In this study, the major burdens are the frequent blood drawings and the cold
exposure. The frequent blood drawings may cause a haematoma after venapuncture.
Even a small puncture when blood is drawn may cause pain or discomfort. Other
risks are swelling of the vein and bleeding or bruising at the site of entry of
the skin. With the use of sterile techniques by trained personnel, these risks
are minimalised.
The frequent blood drawings can potentially be dangerous in the case of
anaemia. Therefore, subjects with a low haemoglobin content will be excluded
during screening. Additionally, an unexpected medical finding can potentially
be detected and participants may feel nauseous after consuming the glucose
drink.

The cold exposure may be perceived as uncomfortable by the participants.
However, this should not inhibit the research from taking place as exercise may
also be perceived as uncomfortable, yet the benefits to health are evident.
This study will provide insight into the effect of a more practical,
individualised cold exposure on glucose tolerance. Although further research
would be required, the research may lead to a new therapeutic option for the
treatment of type 2 diabetes.