At the end of each month, participants underwent a detailed 'thermal metabolic evaluation' in a whole room calorimeter. Measurements taken at the end of the first month represented 'baseline'.
In addition, cold-stimulated PET/CT scans measured brown fat, and muscle and fat biopsies revealed tissue metabolic changes.
Independent of the season during which the study was carried out, brown fat increased during the cool month and fell during the warm month.
Among the metabolic benefits of increased brown fat was heightened insulin sensitivity. This suggests that people with more brown fat require less insulin after a meal to bring their blood sugar levels down.
"The big unknown until this study was whether or not we could actually manipulate brown fat to grow and shrink in a human being," said Dr Lee.
"What we found was that the cold month increased brown fat by around 30-40%."
"During the second thermo-neutral month at 24 degrees, the brown fat dropped back, returning to baseline."
"When we put the temperature up to 27 degrees during the fourth month, the volume of brown fat fell to below that of baseline."
Dr Lee sees promise in brown fat for people with diabetes, whose bodies have to work hard to bring sugar levels down after a meal.
"The improvement in insulin sensitivity accompanying brown fat gain may open new avenues in the treatment of impaired glucose metabolism in the future. On the other hand, the reduction in mild cold exposure from widespread central heating in contemporary society may impair brown fat function and may be a hidden contributor to obesity and metabolic disorders," Lee said.
"Studies have been performed in the UK and US measuring bedroom, dining room and lounge room temperatures in people's homes over the last few decades, and the temperature has climbed from about 19 to 22, a range sufficient to quieten down brown f
|Contact: Alison Heather|
Garvan Institute of Medical Research