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As we approach the colder months, Professor Mike Tipton from the the University of 1024�˹��� and  from University College London have some tips and advice to help people stay warm and save money this winter.

Just stepping up and down on the bottom step of a staircase can produce and additional 200W of heat and raise body temperature in a matter of minutes. However, making heat requires fuel, so ensuring that enough energy dense foods are eaten to meet the demands of heat generation, is important. 

As we get cooler, the blood vessels in our skin shut down, shunting the flow of warm blood deep beneath the insulating layers of fat which we all have. This makes the skin, especially of the extremities, uncomfortably cool, but is an effective strategy for protecting deep body temperature: 2.5cm of fat insulates to a similar degree as a 7mm thick wetsuit. But we can limit loss even further by wearing warm insulating clothing. Mountaineers and polar explorers, of course, can survive comfortably in environmental temperatures well below freezing by wearing the right clothes. 

So, taking some exercise, eating well, and adding some clothing can all help us stay warm. But poverty may limit options for some, and the elderly, sick and disabled may also be more vulnerable. Some medications can lower the body’s energy production, as can some diseases. Age is sometimes associated with loss of muscle mass, which not only normally makes heat, but offers some insulation too.

Metabolic rate at rest is lower in the elderly, and frailty in any form can make it hard to exercise and generate extra heat. The elderly tend to detect and respond to cooling less well than the young. In addition, there are health hazards (for instance, the appearance of fungal mould on walls, which can worsen lung function) if houses are kept too cold. For all of these reasons, current advice is that rooms should be kept at a temperature at or above 18°�� (although this may be less of an issue to the young and healthy). 

So, with winter coming, what do we do to stay healthy and wealthier? We can all act and visit the frail or elderly to help them take action.

Having evolved as tropical animals, a naked resting human is most comfortable in air at 26-28°��, with a deep body temperature of 37°�� and a mean skin temperature of 33°��. Humans are also homeotherms, that is they must maintain their body temperature within tightly constrained limits in order to remain alive and well. They do this biologically and behaviourally, by adjusting both their heat production or inputs, and its loss. 

On average the temperature of indoor environments in high income countries has increased over the decades; reversing this trend and turning the thermostat down can result in energy savings. So, at a time when energy costs are high and unsustainable, can we use what we know about how the body works (physiology) to remain safe and comfortable in cooler indoor environments?

The biochemical reactions which go on in our bodies generate heat as a by-product: at rest, the equivalent of an 80W heater. We can generate more through physical activity: when we exercise, about 25 percent of the ‘chemical work’ we do to power our muscles actually goes to moving us, and about 75 percent is lost as heat.