winter-swimming and brown adipose tissue activity in middel-aged obese subjects (winterbat).

Conditions: Adipose Tissue, Brown; Brown Adipose Tissue; Uncoupling Protein 1; Cold Exposure; Obesity; Type 2 Diabetes Mellitus; Winter Swimming

Summary: this study investigates repetitive cold-water exposure on brown fat activity assessed by pet/ct scanning. furthermore we will assess glucose control upon winter-swimming. obese prediabetic men and women will be randomized to winter-swimming or control conditions for 4 months.

brown fat (bat) is an energy-consuming tissue. long-term activation of bat in adults increases clearance of blood glucose and non-esterified fatty acids (nefa), insulin sensitivity and metabolic rate. moreover, adipokines released from bat, known as batokines, represent a promising but currently unexplored area in terms of metabolic regulation. cooling activates bat; however, current cooling protocols fail to activate bat in a large part of the population. whether this failure in activation is related to biology, inefficient detection or cooling protocols is unknown. with our initial acute cooling study (protocol number: h-16038581), these protocols have successfully been optimized whereupon novel batokines will be identified. having established a methodology for assessing bat activity and batokine profiles, a longer-term cooling intervention (winter swimming) will be performed to examine the effect of repetitive cold-water exposure on bat activity. obese pre-diabetic subjects will be included in a 4-month supervised winter swimming (ws) intervention. it is hypothesized, that repetitive cold-water exposure constituted by ws, increase bat activation and volume, followed by improved glycemic control in obese pre-diabetic subjects. method the study is a randomized controlled, parallel-group intervention study. the investigator will recruit 30 obese pre-diabetic non-winter-swimmers to participate in a ws intervention group (n=15) or control group (n=15) with no ws activities. subjects will either be randomized to the ws group, who will winter-swim 4 months, 2-3 times/week including sauna-visits if desired, or control conditions with no ws during the 4 months (october to may). main aims * to assess whether ws will have an immediate effect on bat recruitment or function. * to assess whether ws will have an effect on glycemic control.

Eligibility criteria:
inclusion criteria: * waist circumference above 80 cm for women and 94 cm for men. * bmi \> 25 but \<40 kg/m2 * age \> 40 years. * low to moderate physical activity level (no physical activity or on average 30 minutes of moderate physical activity per day and not more than 3 hours of training pr. week) subjects will be included in either one of these cases after the screening: * fasting plasma glucose above 5.6 millimol per liter (mmol/l). * hba1c \>39 millimol per mol (mmol/mol). * 2 hour plasma glucose after a 75 g. oral glucose tolerance test (ogtt) above 7.8 mmol/l. exclusion criteria: * winter swimmer * any history of cancer, * clinically significant liver, kidney, heart, inflammatory or lung-disease. * pregnancy * taking medication (not for hay fever), including glucose-lowering treatment. * hba1c \>55 mmol/mol and/or 2-h plasma glucose in the 75-g ogtt \> 15 mmol/l, fasting plasma glucose above 6.9. * iron deficiency * increased international normalised ratio for coagulation (inr). * femoral hernia, vene prostheses (pants prosthesis), thrombs in v. femoralis. * abnormal ultrasound echocardiography of the heart found at the health-examination day. * contraindications to cold exposure including severe raynauds disease. * history of alcohol abuse or use of more than 14 units pr. week. * history of drug abuse, including marihuana. * smoking including occasional smoking. * pacemaker or other electronics implanted in the body. * claustrophobia, communication problems, including understanding the experimental protocol. * history of contrast allergy.