Denmark Mountain Hikers

December 31, 2025

Jacob Schor

I wanted to let you know that we’re going to make a pot of chilli for Friday and probably some corn bread as well.

Then before I knew what I was doing wrote out the following note:

If it seems that the Denmark Mountain Hikers have been easily influenced by the weather of late and prone to canceling hikes based on chilly forecasts, then you are correct in your observations.  While there is a certain kind of joy for some in hiking on a cold crisp day that freezes their nose hairs, these cold days come with  risks that we wish to take into account.  There are the well known risks such as hypothermia, frostbite, and the routine difficulty in performing tasks with chilled extremities. A much greater concern is the recent research confirming a long held suspicion that cold exposure significantly increases risk of death from heart disease.

Let me reference the paper by Fan et al published in 2023 in the Frontiers of Cardiovascular Medicine. full text link: https://pmc.ncbi.nlm.nih.gov/articles/PMC10083291/

Fan JF, Xiao YC, Feng YF, et al. A systematic review and meta-analysis of cold exposure and cardiovascular disease outcomes. Front Cardiovasc Med. 2023;10:1084611. Published 2023 Mar 27. doi:10.3389/fcvm.2023.1084611

Fan’s report was not a study but rather a meta-analysis of data from previously published studies.  Their team of researchers combed through the world’s medical literature for research relate to heart disease risks and cold exposure.  While it is well known that cold exposure raises risk of heart trouble, Fan’s goal was to quantify this and begin to understand the burden that climate change is having and will have on global health. While some think of climate change as just warming temperature, these changes are also associated with instability of normal weather patterns and an increase in frequency, intensity and duration of extreme weather including extreme cold spells.

In total Fan and colleagues identified 159 studies for analysis and incorporation into their analysis. They looked only at original research that explored the association between cold exposure (low temperatures and cold spells) and cardiovascular disease outcomes (that is mortality or morbidity).  They analyzed the combined data to calculate the relative risk of various cardiovascular outcomes per either a 1°C decrease in temperature or a cold spell in the weather.

They report that every 1°C decrease in temperature, increases risk of death from cardiovascular disease by 1.6% (RR 1.016; [95% CI 1.015–1.018]) and morbidity by 1.2% (RR 1.012; [95% CI 1.010–1.014]).

As one reads the actual study one wonders what temperature the authors are measuring from to calculate these decreases.  They use a reference point referred to as the Minimum Mortality Temperature (MMT).  This is not a fixed temperature but  varies by geographical location, the population living there and even by season: a cold day in July is a bigger shock to the system than a cool day in February. Mortality rates fluctuate with temperature, increasing if the temperature is too low or also if it is too high. [i]

 A graph of these data will yield a U-shaped curve..  One might say temperature has a hormetic effect.: too little or too much is a problem.  The MMT is the sweet spot Goldilocks would say is just right.  The temperature where mortality rates are at their lowest point is used as the reference point for these mortality studies. MMT will vary by various factors so each population study gathered in Fan’s meta-analysis will have calculated a MMT to use as its reference  point.

For example, the average MMT for Portland, Maine has been calculated to be 70°F (about 21°C).  Looking at our outdoor thermometer as I type this, it’s -5.5 ° C.  So, we are about 26 degrees below our local MMT.  If Fan et al calculated a 1.6% increase in risk per Celsius degree so, 26 times 1.6%= 41.6 % increase in risk of dying today just from being out in the cold. 

There are things we might do to reduce these cold day risks, aside from moving to warmer climates in the winter.  For people with coronary artery disease (CAD) , cold exposure increases the workload on the heart while at the same time it constricts blood vessels reducing the oxygen supply to the heart. The heart muscle becomes oxygen deficient and this is experienced as angina.

On cold days make a point to avoid getting chilled as this triggers constriction of the blood vessels. Wear extra layers rather than just a single super warm coat.  This allows you to shed clothing as you warm up while hiking.  Don’t shed the layers until you are warm and then be sure to put them back on before you get chilled.  In more moderate temperatures many of us strip down before starting an uphill climb cold.  In cold weather don’t do this; start warm and then stay warm Avoid getting chilled. Shed layers to avoid overheating and getting sweaty

Breathing in cold air chills the blood moving from the lungs to the heart and things would be better off if this weren’t to happen.  A face mask or scarf over the mouth will prewarm your breath and reduce the cold impact on your heart.

Start slow.  Giving your body to warm up, the way you let your car warm up when it’s cold, will reduce the stress on heart and lungs.

Use of blood pressure lowering medications improves exercise performance in the cold for those with CAD or heart failure.  Do not skip medications on cold days.

[iii] Ikäheimo TM. Cardiovascular diseases, cold exposure and exercise. Temperature (Austin). 2018;5(2):123-146. Published 2018 Feb 1. doi:10.1080/23328940.2017.1414014

[iv]

In total, we included 159 studies in the meta-analysis. As a result, every 1°C decrease in temperature increased cardiovascular disease-related mortality by 1.6% (RR 1.016; [95% CI 1.015–1.018]) and morbidity by 1.2% (RR 1.012; [95% CI 1.010–1.014]). The most pronounced effects of low temperatures were observed in the mortality of  ary heart disease (RR 1.015; [95% CI 1.011–1.019]) and the morbidity of aortic aneurysm and dissection (RR 1.026; [95% CI 1.021–1.031]), while the effects were not significant in hypertensive disease outcomes. Notably, we identified climate zone, country income level and age as crucial influential factors in the impact of ambient cold exposure on cardiovascular disease. Moreover, the impact of cold spells on cardiovascular disease outcomes is significant, which increased mortality by 32.4% (RR 1.324; [95% CI 1.2341.421]) and morbidity by 13.8% (RR 1.138; [95% CI 1.015–1.276]).

Conclusion

Cold exposure could be a critical risk factor for cardiovascular diseases, and the cold effect varies between disease types and climate zones.

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[i] Yin Q, Wang J, Ren Z, Li J, Guo Y. Mapping the increased minimum mortality temperatures in the context of global climate change. Nat Commun. 2019 Oct 11;10(1):4640. doi: 10.1038/s41467-019-12663-y. PMID: 31604931; PMCID: PMC6789034.

[ii] Ikäheimo TM. Cardiovascular diseases, cold exposure and exercise. Temperature (Austin). 2018;5(2):123-146. Published 2018 Feb 1. doi:10.1080/23328940.2017.1414014

[iii] Ikäheimo TM. Cardiovascular diseases, cold exposure and exercise. Temperature (Austin). 2018;5(2):123-146. Published 2018 Feb 1. doi:10.1080/23328940.2017.1414014

[iv] Yin Q, Wang J, Ren Z, Li J, Guo Y. Mapping the increased minimum mortality temperatures in the context of global climate change. Nat Commun. 2019 Oct 11;10(1):4640. doi: 10.1038/s41467-019-12663-y. PMID: 31604931; PMCID: PMC6789034.