The opening image is an editorial period scene, not an authenticated portrait or an exercise demonstration.
What the Letter Establishes
Franklin described sitting undressed in his room while reading or writing. His letter is personal testimony, not a controlled health experiment.
What Research Says About Mild Cold Exposure
Scientists have studied what happens when people spend regular time in cool air.
A 2013 study by van der Lans and colleagues placed 17 healthy young adults in a cool room.
The room was kept at 15 to 16 degrees Celsius for 10 days: two hours on day one, four on day two, then six hours on each remaining day.
After those 10 days, the volunteers showed more active brown fat, a tissue that burns energy to make heat.
Their heat production without shivering also went up, from about 10.8 percent to 17.8 percent.
Among the participants who completed comfort ratings, the cold felt warmer and more comfortable by the end.
Their reported shivering dropped as well.
The participants wore shorts and T-shirts. This laboratory schedule did not establish a home starting duration or a benefit from nudity.
What a Large Cold Shower Trial Found
Another line of research looks at short cold exposure, like a cold shower.
In a 2016 trial, Buijze and colleagues enrolled 3,018 working adults.
People were assigned to end their warm shower with 30, 60, or 90 seconds of cold water, or to skip the cold.
The cold shower groups had 29 percent less sickness absence from work than the control group.
But the number of days people actually felt ill did not differ between groups.
The authors also found that regular physical activity was linked with a similar drop in absence.
The trial cannot tell us why reported sick leave differed. It did not show a significant reduction in illness days.
References
- Buijze, G. A., et al. (2016). The effect of cold showering on health and work. Trial report.
- Franklin, B. (1768). Letter to Jacques Barbeu-Dubourg. Primary extract and editor notes.
- van der Lans, A. A. J. J., et al. (2013). Cold acclimation recruits human brown fat and increases nonshivering thermogenesis. Study report.
Health disclaimer: This article is general health information, not medical advice or an individual cold-exposure plan. If you have a medical condition or concerns about cold exposure, talk to a doctor before changing your routine.
