London - We tend to think of our body temperature in the same way that Goldilocks thinks of porridge - it is either too cold, too hot or just right. But scientists have found that being “too hot” or “too cold” can be medically beneficial.
In fact, by altering our temperature we may be able to change crucial aspects of our lives for the better.
The myth of “normal” body temperature
Most people think of normal body temperature as 37 degrees Celcius. This benchmark was set by Dr Carl Wunderlich, a 19th-century German physician, after he took the temperatures of thousands of patients.
However, an American re-evaluation of his work in 1992 found that 36.8 degrees Celcius is more accurate. Such small differences can play a big role in determining things such as a woman’s fertility. Moreover, our normal body temperature changes by as much as 0.6 degrees Celcius through the day. Usually you wake with a cool temperature because your body is rested. As you begin daily activities, it starts to rise.
Older people are often cooler than average, and when they fall ill with an infection their bodies may never reach “normal” fever temperatures. Good Health’s GP, Dr Martin Scurr, explains: “As you get older your body’s ability to regulate its temperature gets less efficient. In very hot weather older people’s bodies don’t sweat and lose heat so well.
“Furthermore, in cold weather they don’t conserve heat that much. It is easier for them to get hypothermia.”
When having a fever is good for you
Having a temperature was traditionally thought of as a bad thing that, in extreme circumstances, could cause serious brain damage and even kill.
But now scientists have discovered that fever helps to boost our bodies’ immune defences - and that for mild illnesses, taking fever-reducing drugs such as paracetamol and ibuprofen makes it more likely we will infect others.
This is because viruses replicate less efficiently in higher temperatures, so fever can lower the amount of virus in a sick person’s body.
Canadian researchers have estimated that in a typical flu season, fever-reducing drugs may lead to tens of thousands more cases.
The guidance from NICE (the National Institute for Health and Care Excellence) is for parents to avoid giving fever-reducing drugs to children unless they look distressed.
Dr Scurr says children with viral infections can look very worrying to parents. ‘But if you unwrap them from their clothes and bedclothes and put a fan on them or bathe them quickly in lukewarm water, it can lower their temperature significantly.’
Hot women are more fertile
Raised temperature in a woman is a sign that she is at the most fertile part of her monthly cycle. It rises by about 0.2 degrees Celcius just after ovulation. This is thought to be due to raised levels of fertility hormones, including progesterone.
Women who are trying to conceive often use a basal thermometer (which has a finer scale than a normal one) to help them pinpoint when they are ovulating - and cellphone technology may make this more precise, as new apps use sensors worn on the skin to monitor a woman’s temperature throughout the day.
“These may help to get a more accurate idea of when fertility is peaking,” says Dr Allan Pacey, a fertility expert at the University of Sheffield. But he stresses that it still isn’t foolproof.
“You can’t predict when you’re going to be most fertile from temperature - only that it’s already happening.”
It is also tight timing, as there is only a 24-hour window from ovulation when the egg is viable. “Realistically, you may not end up taking a temperature reading until 12 hours into that window - or you could miss it altogether. Regular sex is still a more reliable method.’
Men need to be chilled to conceive
Men trying to become fathers should keep their testes cool. These need to be a degree or two below normal body temperature for sperm to form properly - which is why they are outside the body.
‘If men take regular hot baths - anything significantly above lukewarm - or spend long periods driving a car with heated seats or with a laptop on their lap, this could heat the testes enough to reduce quality and motility of sperm,’ says Yasmin Sajjad, a director of the IVF centre at St Mary’s Hospital, Manchester.
Research has shown that boxer shorts keep testes cool better than briefs.
Menopausal women feel worse at 6.25pm
Menopausal hot flushes are determined partially by a woman’s 24-hour body clock - and the peak time for her to ask “Is it hot in here?” is 6.25pm, according to a recent study.
Body temperature can fluctuate by 9 degrees Celcius during a hot flush, causing sweating and problems sleeping if it happens at night.
Three-quarters of menopausal women have hot flushes. Although this is a nuisance, there is a positive side - they may lower the risk of cardiovascular disease and stroke.
A Harvard Medical School study that followed 60 000 women for a decade found that those who had hot flushes when they began the menopause had fewer cardiovascular events than those who experienced flushes late in menopause or not at all, reported the journal Menopause in 2011.
More research is needed to understand why this is.
Turn the heating down, lose weight
Feeling cold might help you to lose weight. Being cold and shivery can make us burn more calories to try to generate heat - and last month scientists also reported that cold temperatures can set off an immune reaction that converts energy-storing white fat - the sort that makes plump tums and dimpled thighs - into brown fat that burns up energy.
Babies have lots of brown fat to keep their temperature stable. As we age it almost all disappears. But now a study in the journal Cell has found that cold temperatures trigger our bodies to convert some white fat into a ‘browned’ form called beige fat.
Until science can create a fat-burning pill, just turn down the central heating to 19c. The average house thermostat is set at 23 degrees Celcius - that’s too warm.
Stay cool and you may live longer
The Baltimore Longitudinal Study of Aging, published in the journal Science in 2002, reported that men with a below-average core body temperature lived longer than men with above-average body temperature.
One theory is that a lower body temperature may produce fewer free-radical compounds that could damage cells and promote ageing.