But sustained periods of heat do more than that – they age us faster. Cumulative heat stress changes our epigenetics – how our cells turn on or off gene switches in response to environmental pressure.

Now, new research from the United States explores the pressing question of how extreme heat affects humans. The findings are concerning. The more days of intense heat a participant endured, the faster they aged. Longer periods of extreme heat accelerated ageing in older people by more than two years.

How, exactly, does heat age us?
Ageing is natural. But the rate of ageing varies from human to human. As we go through life, our bodies are affected by stresses and shocks. For instance, if we don’t get enough sleep over a long period, we will age faster.

What does that look like on a genetic level? You might think your genes don’t change over your life, and this is mostly true (apart from random mutations).

But what does change is how your genes are expressed. That is, while your DNA stays the same, your cells can switch some of its thousands of genes off or on in response to stresses. At any one time, only a fraction of the genes in any cell are turned on – meaning they are busy making proteins.

This is known as epigenetics. The most common and best understood pathway here is called DNA methylation (DNAm). Methylation here refers to a chemical our cells can use to block a DNA sequence from activating and producing proteins with various functions. Cellular changes in DNAm can lead to proteins being produced more or less, which in turn can flow on to affect physiological functions and our health status. This can be both bad or good.

To date, much research on how heat affects epigenetics has focused on animals and plants. Here, the evidence is clear – even a single episode of extreme heat has been shown to have a long-lasting effect on mice.

What did the study find?

The study set out to better understand what happens to human bodies at a biological level when they’re exposed to intense heat over the short, medium and longer term.

To do this, the researchers took blood samples and measured epigenetic changes at thousands of sites across the genome, which were used to calculate three clocks measuring biological age, named PcPhenoAge, PCGrimAge and DunedinPACE.

We need to know more

Perhaps surprisingly, there has been little research done to date on what heat does to human epigenetics.

In 2020, we conducted a systemic review of the science of how environment affects human epigenetics. We found only seven studies, with most focused on the effect of cold rather than heat.

Now we have this new research which sheds light on the extent to which heat ages us.

As we face a warmer future, our epigenetics will change in response. There is still a lot of work to do to see how we can adapt to these changes – or if we even can, in some parts of the world.

Source: https://findanexpert.unimelb.edu.au/news/100235-intense-heat-changes-our-biology-and-can-make-us-age-significantly-faster--study