Blood sugar levels too high? Turn down your central heating!

ThE changing of the seasons can pass you by — if you stay indoors. Over the past 40 years homes have been getting warmer in winter and cooler in summer.

household temperatures during colder months average 18C — up from a mere 12c in the Seventies — as we rely on central heating. And as sales of domestic air conditioners have risen by 400 per cent since 2000, we no longer have to feel the heat in the summer.

But while this has made us more comfortable, has it been harmful to our health? research suggests our bodies need to feel a range of hot and cold conditions each day. So spending our lives in offices and houses where the temperature hardly changes may be bad news for our health — and make us fatter.

Last week, a study by scientists at maastricht University in the netherlands showed changes in temperature can affect patients with type 2 diabetes as much as common medicines.

researchers repeatedly moved patients between rooms where the temperature averaged a snug 21c or fell within a chillier 15c to 19c.

the patients’ sensitivity to insulin — the hormone that keeps blood sugar at a healthy level — increased by more than 40 per cent.

normally, doctors prescribe type 2 diabetics drugs such as metformin to improve the body’s use of insulin.

But the Dutch study, published in Building research and information, suggests turning the thermostat down by 5c or 6c for two hours a day in winter can be just as effective.

Moving between the temperatures speeds up the rate at which the body burns calories, say the researchers. this creates energy that generates warmth and may make cells more responsive to insulin.

‘ it has previously been assumed that stable indoor temperatures would satisfy comfort and health,’ says study leader Wouter van marken Lichtenbelt, Professor of Ecological Energetics and health at maastricht University.

‘ however, this research indicates that mild cold and variable temperatures may have a positive effect.’

the maastricht team believe we need to rethink our attitude to heating. they say ‘thermo-neutral’ conditions with hardly any change in climate mean the body has to expend little energy to maintain its core temperature.

it’s not the first time this idea has been raised. in 2010, scientists writing in medical hypotheses said they believed the fact that people work in temperatures close to their body temperature is a ‘causal factor in global obesity’.

Any change of temperature, hotter or colder, makes us burn more calories.

‘A 6c drop in temperature can help the body to burn an extra 167 calories,’ says Dr thomas Barber, a consultant endocrinologist at University hospitals Coventry and Warwickshire nhS trust.

Even small swaps in temperature help by encouraging a process called nonshivering thermogenesis.

While shivering to create body heat happens when the temperature drops by 6c or 7c, non-shivering thermogenesis can occur with a relatively small drop of just 1c or 2c.

it triggers the burning of ‘ brown’ fat — a type of fat found mainly around the neck — which turns food into body heat.

But now we spend months in buildings, where we hardly ever change the temperature, this rarely happens.

‘in the early Seventies, only one in three houses had central heating,’ says Dr Barber. ‘ Average household temperatures have gone up by about 6c.

‘that would have had an impact on energy expenditure and it’s possible it has contributed to weight gain.’

it seems any constant temperature can cause problems — even when it involves chilly temperatures.

Scientists at the national Yang- ming University in taiwan found that sleeping with the air conditioning on causes blood pressure to soar in the early morning.

they measured the blood pressure of 24 men in their mid-20s every 30 minutes as they slept in rooms chilled to 16c, and compared the readings to those taken when the same people slept in rooms heated to 24c.

the study, in PLOS One, found that blood pressure in the morning was significantly higher after having the air conditioning on all night as lower temperatures cause blood vessels to narrow.

So when it comes to controlling the heat of your home, the answer seems to be to keep it like the British climate: changeable.