Not So Hot: Why The Average Body Temperature Fell from 98.6

Why are we cooler than our ancestors - and why should wediscover the average Indian human temperature?

Health News
5 min read
Not So Hot: Why The Average Body Temperature Fell from 98.6

You know when you're feeling under the weather and you bring out your thermometer to check? 'Phew,' you breathe a sigh of relief, '98.6.'

The universal normal, average temperature that signalled all was well has been relied on for as long as we can remember.

But now, researchers at Standford argue that today's universal average stands at a slightly lower 97.5 degrees. Another study from Britain also put the number at around 97.88 degrees.

What does it mean when an assumed standard for an entire species changes? And can our average body temperature really change?

Our body’s temperature is roughly linked to our metabolic rate - and how tall we are, how fat we may get and health problems we could face. So what does a changing body temperature mean for our physical health?

FIT spoke to Dr Ashwini Setya, Programme Director in Delhi’s Max Super Speciality Hospital, who told us to halt the theatrics - it’s not really such a big deal. He said what could make a difference is if we use these findings to dig deeper for more specific research and those results would be more interesting.


Why is Our Temperature Falling?

The evidence suggests a change, but why exactly are we cooler than our ancestors?

Dr Ashwini Setya explained, “Even back in the late 19th century when this number (98.6) was arrived at, statistical instruments (mean, median, mode, standard deviation) were used to arrive at an average, and so the standard deviation was always there.”

In plain speak, he says,

“The average is and was never an absolute value. It is a range as it varies with many factors both internal and external. As a doctor, I know there are always outliers outside this range too. I’ll have a patient come in who will say he’s feeling feverish but the thermometer reading is normal. Is he lying? Of course not, some people have a different basal temperature depending on their individual metabolic rate”

Yes, he agrees that the latest findings indicate a trend toward a lower average, adding, “There could be many reasons for this as both evolutionary and socio-environmental factors play a role in contributing to your body’s temperature. as a species, we have become taller and so there could be more heat loss (specific to gender) which could contribute to a lower base temperature.”

Vox spoke to Stanford researcher Catherine Ley, who co-authored the research, to find out why these changes have happened. Her answer? “We don’t know.”

That’s honest. The hypothesis is that it’s an indicator for increased health - which is true, as a species we have grown healthier and live longer than ever before due to advancements in technology, awareness, hygiene, immunization and medical improvements.

Ley says that our advancements in vaccination that reduced the potency of tuberculosis had a huge impact on our bodies - besides saving more of us, it affected our average temperature too.

In an article on LiveScience, another co-author of the Standford study, senior researcher Dr Julie Parsonnet estimates that this global decline could reflect the decrease in infectious disease rates. How? Inflammation in the body creates proteins called cytokines that push up your metabolic rate and generate heat and so less overall infection, leads to less inflammation and less heat in our bodies.

Plus we now, more than ever before, live in temperature-controlled worlds - although much of the developing world doesn't have access to this as much.

What’s ‘Universal’ About it Anyway?

Let’s debunk the myth of the ‘universal global average.’ Humans are varied, and age, region and even time of the day can greatly impact your resting body temperature. So not only do different populations of people register slight variations in their temperature, the same person goes through many normal fluctuations as well.

So how did we come up with 98.6?

According to an article from the Wall Street Journal, this number was determined almost 150 years ago from a sample of just 25,000 people by a German physician called Carl Reinhold August Wunderlich.

If you think it may be time to update this 'universal standard' to modern humans, you're not alone. According to a recent study from Standford University, while 98.6 was representative in 1869, human bodies have evolved - maybe enough to result in a change in the average body temperature.

The latest Stanford researchers analysed samples from almost 200,000 individuals in the US for over 157 years - looking at Civil War veteran records from the 1940s to the 2017 database. They found a declining average over the years, as the decades passed.

Now whenever an idea is re-tested, it's prudent to scrutinise how. This is especially important for scientific studies that often use different methods or instruments or make other changes in data collection that make comparisons complicated.

Take temperature for example - how do you check your own? Most adults place a thermometer under their tongue or armpit, but for children, it's often the ear and for complicated cases, it is even the rectum. Now while each reading will yield roughly the same temperature, ear and rectal temperatures are often higher by half or one degree - seems small but makes a big difference in contributing towards the global average.

India Specific Research

We’re always talking about universal when we really mean American/European - all of the studies mentioned so far have a sample size made up of these populations.

In another study, this time focussed in Pakistan in 2008, the average temperature was still found to be 98.6 degrees.

Is it time for India to develop research to determine our own, specific average?

Dr Setya adds, “The fact about the body temperature changing due to our temperature-controlled lifestyle is not true for Indians. We have different factors affecting us - we’re an agricultural society who mostly don’t spend their time indoors, we do more manual labour on the whole, sweat more and regulate our body like that.”

He says,

“We need India specific research. Here we have people who can regulate their body’s anatomic phenomenons themselves. For example, many yogis can control their own body temperature, blood pressure and more. Yoga is more than just asanas!”

Temperature, and Bodies, Are Complex

There are many diverse things that impact our body temperature - from the foods you eat to seasonal changes to where you stay at the time of temperature collection.

Besides, women often have a resting temperature that’s slightly cooler to men - although this is impacted by weight, differing metabolic rates and hormonal changes or menstruation. This is perhaps why women are colder in office spaces too.

Dr Setya says that temperature is often a natural way to track women’s menstrual cycles, “Women’s body temperature increases by around 0.5 degrees on the day of ovulation. This is a totally normal, helpful change in temperature.”

According to the Standford study, “the mean body temperature in men and women, after adjusting for age, height, weight and, in some models date and time of day, has decreased monotonically by 0.03°C per birth decade.” So we get colder as we age too.

From internal changes to external ones, this really begs the question: can we really have one universal standard?

“Your average temperature really depends on who you are,” says Ley to Vox.

But what does this mean for us and for doctors, especially since as patients we often rely on our temperature to quantify how sick we are.

“For me, the importance of these findings are the implications for patients,” says Dr Setya.

“Will I change the treatment pattern due to this? No, since we always have treated people with an understanding of the range of ‘average’ temperature. ”

It’s too soon for the “hullaballoo” over these findings, but Dr Setya says he is interested in more specific research. “Maybe it will be able to indicate how long we live? We don’t know yet.”

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