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For generations, we were told the number that meant a “healthy” body was 98.6 degrees Fahrenheit or 37 degrees Celsius. That figure came from 19th-century measurements, but researchers are finding that it no longer describes most of us. 

One such independent researcher is named Matthew Cormier, and he has just published a review in the Journal of Independent Medicine arguing that average human body temperature has fallen nearly a full degree since the 1800s—to about 97.7 today—and that the drop tracks a broader metabolic and immunological problem. 

Cormier’s paper reviews 48 published studies. The decline shows up in U.S. records stretching from Civil War veterans to modern Stanford patients, and it appears in data from Japan, Canada, and Bolivia. It is visible in children and in middle-aged adults. Researchers have tested the usual objections—thermometer changes, air conditioning, simply being heavier—and none of them fully account for the drop. 

One of the sharper data points comes from the Tsimane (chee-MAY-nay), an indigenous population in Bolivia. In the early 2000s, their average temperature sat at the old 98.6 benchmark, and they had some of the healthiest hearts ever recorded. By 2018, without air conditioning or electricity, it had fallen to about 97.7… in just 16 years.  

If temperature is a readout of metabolic health, that rapid shift is hard to dismiss as evolutionary fine-tuning. 

Body temperature is a vital sign because it reflects how efficiently we produce heat—our basal metabolic rate—and how well we maintain the thermal barrier that keeps many pathogens in check. Cormier calls that barrier a “thermal exclusion zone.” Heat has been a survival advantage for hundreds of millions of years. Many fungi, bacteria, and parasites simply do not thrive at normal mammalian temperatures. 

Over the same decades the population cooled, the chronic-illness numbers moved the other way.  

U.S. diagnosed type 2 diabetes rose from 5.7 million people in 1980 to 38 million by 2021. Global diabetes climbed from roughly 200 million in 1990 to 830 million in 2022. About two in five American adults now have prediabetes. Only around 12 percent of U.S. adults meet standard criteria for metabolic health, that is, healthy levels of blood pressure, blood sugar, cholesterol, and waist circumference without the need for medication. 

Estimates cited in the review put 40 to 50 percent of American children in the category of at least one chronic condition. Invasive fungal deaths are also estimated in the millions annually. The paper does not claim the temperature drop causes every one of those conditions; rather, it treats temperature as a biomarker—a lesser-known sign that the body is under stress.  

Early 20th-century gains from sanitation and antibiotics reduced acute infections, making the continued decline in body temperature harder to explain as simply a product of evolution or improved survival. 

Some of the things that Cormier flags as potential contributors to this include heavy-metal exposures (cadmium, lead, arsenic appearing in commercial products, including some baby foods) and repeated antibiotic disruption of the gut microbiome—both expanding across the same historical window as the temperature decline. 

None of this means you should panic over a single thermometer reading. Individual temperatures vary. But a population-wide drop of nearly a degree deserves more than a shrug—especially as metabolic disease and chronic illness continue to rise. 

Check your own resting temperature over a few mornings. Maybe 97.7°F is the new normal. But that doesn’t necessarily mean it’s the optimal one.