Keeping warm - 1

Regarding warmth we're only 25 per cent efficient, with 75 per cent of the energy we produce being released as heat.

Although we feel hot and cold throughout the day, our core body temperature - that of our vital organs - is always kept at about 37C.

Maintaining this temperature is vital to survival: a 2Cdrop can cause hypothermia, a 12C drop results in death.

Our extremities dictate how hot or cold we feel; the temperature in our hands and feet varies widely compared with that of our organs.

If our hands or feet are chilly, we'll feel cold.

Most of our biological temperature sensors are located in the skin, and we have four times as many cold sensors as hot sensors.

Our heightened sensitivity to cold makes a chilly draught invariably feel more uncomfortable than a warm breeze.

And women really do feel the cold more than men, but this is because they are better at conserving heat than men.

Mark Newton, a scientist at W.L. Gore, the company that makes Gore-Tex, and a researcher at the University of Portsmouth, explains:

“Women have a more evenly distributed fat layer and can pull all their blood back to their core organs.”

However, this female heating system means that less blood flows to their hands and feet, and as a result they feel cold.

So there is literal truth in the old saying cold hands, warm heart.

One theory as to why women have evolved this system, says Newton, is to enable them to survive freezing temperatures.

Women carry less fat and muscle mass than men, and so need a more efficient technique of protecting their core body temperature.

Research also indicates that women's perception of cold varies during their menstrual cycle, says Newton, with the core body temperature often changing by more than 1C.

A study in 2001 found that women's core temperature rises in the luteal phase (the post-ovulation phase) of the cycle.

The researchers also found that women on the Pill have a slightly elevated core body temperature.

But it's not only hormones that can muck around with our biological thermostats; sleep can also affect how chilly or hot we feel.

When we are tired we're more sensitive to changes in temperature, says Newton.

Our body temperature falls at night, with women reaching their minimum body temperature quicker than men.

But what else determines our temperatures, apart from gender?

Diet can make a difference, as can a host of other factors, says Professor Tipton.

“People who are fatter tend to have cooler extremities because their skin is insulated from their body heat by a layer of fat.

People who are physically active tend to have higher peripheral temperature because they have better blood flow to extremities.

Those people who smoke may have lower extremity temperatures, because they may have poor circulation.”

Moreover, how hot or cold we feel also depends on the temperature we're used to living in,

Professor Tipton adds. If you spend a lot of time in a cold house, going to a warm house will be a shock to the system, even if others insist that the temperature is normal.

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