Most of us expect to become more sensitive to cold as we get older. We reach for a sweater sooner. A room that once felt comfortable suddenly feels chilly. Scientists have long known that aging can weaken the body’s ability to produce heat, but the biological reasons have remained difficult to pin down.
Unlike white fat, which primarily stores energy, thermogenic fat is a special type of body fat that burns calories to produce heat and helps us stay warm. Learning how the body controls this process may offer insights into obesity, type 2 diabetes and other metabolic disorders.
Thermogenic fat tends to become less active with age, which may explain why older people are more sensitive to cold.
Our new study in Nature reveals how signals from nerves and immune cells control how much heat thermogenic fat produces by changing the balance between highly active and less active fat cells. Experiments in mice suggest that this system becomes less flexible with age, leaving thermogenic fat slower to respond when temperatures fall.
Previously, we found that thermogenic fat cells vary in how much heat they produce. Some have high levels of UCP1, a protein that generates heat, while others have less UCP1 and remain less active. In this study, we observed a similar mix in human thermogenic fat samples, although we conducted most of our experiments in mice.
How the Body Turns Up the Heat
This mix of thermogenic fat cells may give the body a built-in way to adjust to changing temperatures. When more warmth is needed, signals from the nervous and immune systems prompt less-active cells to increase heat production. When the need passes, the system can dial that activity back.
In older mice, however, this response became sluggish. Their thermogenic fat could still increase heat production, but it took longer. As a result, the animals had more difficulty maintaining their body temperature during cold exposure.
We were able to restore some heat production in older mice by blocking one part of the biological pathway behind this slowdown. The treated animals produced more heat and burned more energy.
The drug used in the experiment, mifepristone, affects many parts of the body, so it is not a treatment for age-related cold sensitivity. But the results suggest that the decline in thermogenic fat activity could be reversed.
That possibility matters for more than staying warm. Thermogenic fat also burns glucose and fat, and its activity tends to decline with age. If scientists can find a safe, precise way to restore that activity, this foundational research could eventually deepen our understanding of age-related metabolic problems, including obesity and type 2 diabetes.
About the Author
Qiong “Annabel” Wang, Ph.D., is an associate professor at City of Hope’s Arthur Riggs Diabetes & Metabolism Research Institute. Her expertise includes fat cell development and accumulation, heat production by thermogenic fat and the cellular mechanisms connecting aging, fat tissue dysfunction and metabolic diseases such as obesity and type 2 diabetes.