Body temperature would seem to have an almost intuitive connection to lifespan. One of the original theories of aging was a metabolic one: the faster an organism burns, the sooner it burns out. Therefore a higher body temperature would correlate with a lower lifespan. In humans, this turns out to be the case.
Reduction of body temperature has been proposed to contribute to the increased lifespan in calorie restricted animals and mice overexpressing the uncoupling protein-2 in hypocretin neurons. However, nothing is known regarding the long-term effects of calorie restriction (CR) with adequate nutrition on body temperature in humans. In this study, 24-hour core body temperature was measured every minute by using ingested telemetric capsules in 24 men and women (mean age 53.7±9.4 yrs) consuming a CR diet for an average of 6 years, 24 age- and sex-matched sedentary (WD) and 24 body fat-matched exercise-trained (EX) volunteers, who were eating Western diets. The CR and EX groups were significantly leaner than the WD group. Energy intake was lower in the CR group (1769±348 kcal/d) than in the WD (2302±668 kcal/d) and EX (2798±760 kcal/d) groups (P<0.0001). Mean 24-hour, day-time and night-time core body temperatures were all significantly lower in the CR group than in the WD and EX groups (P≤0.01). Long-term CR with adequate nutrition in lean and weight-stable healthy humans is associated with a sustained reduction in core body temperature, similar to that found in CR rodents and monkeys. This adaptation is likely due to CR itself, rather than to leanness, and may be involved in slowing the rate of aging.
The study found that leanness that resulted from calorie restriction – but not leanness that resulted from exercise – was correlated with low body temperature.
The chart above shows the correlation between body fat percent and core temperature. The article also contains this statement: “In the Baltimore Longitudinal Study of Aging (BLSA) men with a core body temperature below the median lived significantly longer than men with body temperature above the median in the absence of CR .”
The study referred to is this one: Biomarkers of Caloric Restriction May Predict Longevity in Humans. The study notes three important biomarkers that are associated with longer life in calorie-restricted animals, body temperature (lower), plasma insulin levels (lower), and DHEA levels (higher). Then – here’s the interesting part – they looked at these biomarkers in aging humans, and plotted these against their survival curves. Results below:
What you see here is that in humans, who were not calorie restricted, lower body temperature and insulin, and higher DHEA levels, correlated with survival.
So, calorie restriction changes levels of these three important biomarkers, and in turn these biomarkers are correlated with longevity, even in the absence of calorie restriction.
For longer life, one wants to keep these biomarkers at levels that correlate with longevity. An easier, and probably all around better way to do this than calorie restriction is through intermittent fasting, which has virtually the same effects on these markers as calorie restriction, with the added advantage (and it’s a big one) that you don’t feel like you’re starving yourself all the time. Intermittent fasting will keep insulin levels and body temp lower, and DHEA levels higher.