Summer Heat and Longevity: 6 Surprising Ways Warmth Strengthens You by Jayney Goddard, MSc, PG DipEd, FCMA, FRSM. Founder and President, the Complementary Medical Association

I’m writing this in what I believe is the fourth heat wave of the summer here in the South of England. Of course, we are all very aware of the catastrophic wildfires that are popping up all over the place in Europe and here in the UK, further afield too, of course, in the USA. Many people I speak to are thoroughly are fed up with the excessive heat, particularly those of us in Europe, where we don’t tend to have air conditioning. So, I wanted to bring a little bit of good news amidst the sweat, and that is that warmth strengthens you! It’s a topic that not many people know about, so I thought I’d share the latest findings. Hopefully this will enable us all to find a grain of positivity in the current situation.

This is not an invitation to bake yourself on a lounger with no shade in sight — quite the opposite, as you will see. But the science of “hormesis” — the idea that mild, well-managed stressors can trigger the body’s own repair and resilience systems — offers a genuinely interesting lens on why sauna cultures, hot springs, and warm-climate longevity have long been linked in folk wisdom, and what the modern evidence does and does not support.

What Is Hormesis? The Biology of “Good Stress”

Hormesis describes a U-shaped relationship between a stressor and a biological outcome: too little produces no benefit, too much causes harm, but a moderate, well-timed dose can stimulate the body’s own protective and repair pathways.³ We already understand this well in the context of resistance training, where the micro-stress of lifting a weight prompts muscle tissue to rebuild stronger than before. Exercise remains, in my view, the single most reliable hormetic tool we have for healthy ageing, with heat exposure sitting alongside it as a supporting — not replacement — strategy.

Heat appears to work on the body in a similar fashion. When core temperature rises moderately, cells respond by producing heat shock proteins, activating vascular adaptations, and triggering a cascade of repair processes that researchers believe may echo some of the benefits of physical exercise.

1. Heat Shock Proteins: Your Cells’ Emergency Repair Crew

Heat shock proteins (HSPs) are molecular chaperones first identified for their role in the body’s response to thermal stress. Their job is to refold or clear away damaged and misfolded proteins before they accumulate and cause cellular dysfunction — a process implicated in several age-related conditions.³ Reviews of hormetic ageing research describe HSP induction as one of the most consistently observed hormetic mechanisms across species, from yeast to mammals.³

It would be lovely to say the case is closed, but honest reporting means telling you where the evidence is more nuanced. A meta-analysis pooling 27 studies across 12 animal species found that, contrary to expectations, heat shock exposure did not measurably extend longevity when all the data were combined — and that higher temperatures, longer exposures and more frequent repeated shocks actually reduced the likelihood of any life-extending effect.⁴ The authors concluded that if heat-induced hormesis benefits longevity at all, it likely does so only within a narrow window of mild, moderate exposure — which is precisely why the practical guidance later in this piece matters more than the underlying biochemistry.

2. Sauna Bathing and Cardiovascular Longevity — the Finnish Evidence

The most robust human data on heat and longevity comes from Finland, where sauna bathing is woven into daily life. In a prospective cohort study following over 1,600 adults for a median of 15 years, researchers found that cardiovascular mortality risk decreased in a linear, dose-dependent fashion with more frequent sauna sessions, with no threshold effect observed.¹ Compared with once-weekly sauna use, those bathing four to seven times a week had a substantially lower risk of cardiovascular death, even after adjusting for established risk factors such as blood pressure, cholesterol and physical activity.¹

A separate analysis of the same Finnish cohorts found that frequent sauna bathing was also associated with a reduced risk of stroke.² The proposed mechanisms include improved heart rate variability, reduced arterial stiffness, and short-term reductions in blood pressure — effects that plausibly compound over years of regular use.

3. Passive Heat Therapy and Blood Vessel Health

Where sauna research is largely observational, controlled trials of hot water immersion — sometimes called passive heat therapy — give us a clearer window into mechanism. In one trial, previously sedentary adults who completed eight weeks of repeated hot water immersion (40.5°C, sufficient to raise core temperature to 38.5°C, for an hour, four to five times weekly) showed almost a doubling of flow-mediated dilation — a key marker of healthy blood vessel function — alongside reduced arterial stiffness, thinner carotid artery walls, and lower blood pressure.⁵ The changes were, notably, on par with or greater than what is typically seen from an exercise training programme of similar length — though the researchers were clear this makes heat therapy a complement to exercise for those with limited mobility, not a substitute for it.

4. Hydration: The Overlooked Longevity Lever of Summer

If heat has a genuine longevity upside, hydration is very much the other side of that coin — and it is where I think most of us have the most straightforward win available this summer. Researchers at the US National Institutes of Health followed more than 11,000 adults over 25 years, tracking serum sodium — a marker that rises when fluid intake falls — against measures of biological ageing. Adults with serum sodium at the higher end of the normal range were found to be up to 50% more likely to show a biological age greater than their years, and to face an increased risk of chronic disease and earlier death, compared with those in the medium range.⁶ The researchers were careful to note that this is an association, not proof of direct cause, and that confirming the link will require dedicated clinical trials — but as a low-risk, low-cost intervention, keeping well hydrated across the summer months seems a sensible precaution while that fuller picture emerges.

In practice, this means leaning on water-rich, plant-forward foods — cucumber, melon, tomatoes, courgette, leafy salads — alongside plain water and herbal teas, particularly on warmer days when insensible fluid losses through the skin rise without our always noticing.

5. A Word of Caution: Who Should Be Careful with Heat

I would not be doing my job properly if I did not pair all of the above with a clear caveat, because heat is not universally benign, and British summers increasingly bring genuine heatwave conditions. An analysis of the 2020 heatwaves in England found significant excess mortality concentrated in adults aged 65 and over, with cardiovascular disease, respiratory disease, and dementia among the leading causes of heat-related excess deaths.⁷ The same research noted that a large share of those deaths occurred at home, often in dwellings that had overheated, underlining how important it is to manage indoor temperature as well as personal heat exposure.⁷

Older adults, those with cardiovascular or respiratory conditions, and anyone taking medications that affect fluid balance or the body’s ability to regulate temperature should take particular care in hot weather, and should always seek individual medical guidance before starting a sauna or heat therapy routine of any kind.

How to Bring This Into Your Summer, Sensibly

Drawing the threads together, here is how I think about applying this evidence in daily life, always tailored to the individual:

• Keep it mild and habitual, not extreme and occasional. The strongest evidence comes from regular, moderate heat exposure over months and years — not from one punishing session.
• Hydrate proactively, not reactively. Drink ahead of thirst on hot days, and favour water-rich plant foods alongside plain water.
• Pair heat with movement, not instead of it. Resistance training remains the primary intervention for healthy ageing; heat exposure is a supporting act, not a substitute.
• Cool your bedroom at night. The research on 2020’s heatwaves specifically flagged high night-time temperatures as a driver of excess mortality — ventilation and shading matter as much as anything you do outdoors.
• Get individual guidance if you fall into a higher-risk group. Age, cardiovascular health, respiratory conditions and certain medications all change the calculus, and a tailored plan matters far more here than generic advice.

As with so much in longevity science, the most exciting individual finding rarely tells the whole story on its own — it is how these pieces fit your particular physiology, medical history and lifestyle that determines whether they help or hinder.

Do please let me know below whether you have found this interesting and helpful, and of course any other topics that you would like me to look at for you

With love and in strength,
Jayney xoxo

Frequently Asked Questions About Summer Heat and Longevity

Is sauna use good for longevity?

Large Finnish cohort studies link frequent sauna bathing with significantly reduced cardiovascular mortality and stroke risk, in a dose-dependent way — though as with all observational research, this shows association rather than definitive proof of cause.^1,2

What are heat shock proteins and why do they matter for ageing?

They are the cell’s repair chaperones, cleared into action by mild thermal stress. The mechanism is well established; whether it reliably extends human lifespan is still an open question, with animal evidence genuinely mixed.^3,4

How much water should I drink in summer to support healthy ageing?

General guidance suggests around 1.5–2.2 litres daily for women and 2–3 litres for men, adjusted upward in hot weather — though individual needs vary with health status, medication and activity level.⁶

Who should be cautious about heat exposure in summer?

Adults over 65, those with cardiovascular or respiratory conditions, and anyone on medication affecting fluid balance or thermoregulation should take particular care, and seek individual medical advice.⁷

Medical Disclaimer

This article is provided for general educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making changes to your health routine, particularly if you have an existing medical condition, are pregnant, or are taking medication.

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About the Author

Jayney Goddard MSc, PG Dip Ed, FCMA, FRSM is the Founder and President of The Complementary Medical Association (The CMA), the world’s leading professional body for complementary medicine. With more than three decades at the forefront of complementary and integrative healthcare, Jayney has dedicated her career to raising professional standards across the sector and to championing rigorous, evidence-based natural approaches to health and longevity. She is the author of several best-sellers, including Rewind Your Body Clock – the Complete Natural Guide to a Happier, Healthier, Younger You (Watkins/Penguin Random House), which debuted on the Amazon charts at No. 1 among ALL books on the platform. Jayney is a sought-after international speaker and a passionate advocate for the safe, ethical integration of complementary medicine within mainstream healthcare. Through The CMA, she supports a global community of Practitioners, Fellows, and Approved Suppliers committed to the very highest standards of practice.

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Further Reading

• Muscle and Longevity: Why It’s the Most Important Organ You’re Ignoring
• Urolithin A: 5 Breakthrough Discoveries
• Five Remarkable Health Benefits of Awe

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References

1. Kunutsor SK, Khan H, Zaccardi F, Laukkanen T, Willeit P, Laukkanen JA. Sauna bathing reduces the risk of stroke in Finnish men and women: a prospective cohort study. Neurology. 2018;90(22):e1937–e1944. DOI: 10.1212/WNL.0000000000005606
2. Heat shock proteins and hormesis in the diagnosis and treatment of neurodegenerative diseases. Immunity & Ageing. 2015;12:20. DOI: 10.1186/s12979-015-0046-8
3. Life extension after heat shock exposure: assessing meta-analytic evidence for hormesis. Ageing Research Reviews. 2013;12(2):653–660. DOI: 10.1016/j.arr.2013.03.005
4. Brunt VE, Howard MJ, Francisco MA, Ely BR, Minson CT. Passive heat therapy improves endothelial function, arterial stiffness and blood pressure in sedentary humans. The Journal of Physiology. 2016;594(18):5329–5342. DOI: 10.1113/JP272453
5. Dmitrieva NI, Gagarin A, Liu D, Wu CO, Boehm M. Middle-age high normal serum sodium as a risk factor for accelerated biological aging, chronic diseases, and premature mortality. eBioMedicine. 2023;87:104404. DOI: 10.1016/j.ebiom.2022.104404
6. Thompson R, Landeg O, Kar-Purkayastha I, Hajat S, Kovats S, O’Connell E. Heatwave Mortality in Summer 2020 in England: An Observational Study. International Journal of Environmental Research and Public Health. 2022;19(10):6123. DOI: 10.3390/ijerph19106123