While 98.6 degrees Fahrenheit is often cited as the standard for normal body temperature, adults' average body temperature may be closer to 97.9 degrees Fahrenheit, according to a study published Sept. 5 in JAMA Internal Medicine.
Researchers analyzed data on 396,195 outpatient encounters at Stanford (Calif.) Health Care that included temperature measurements from April 28, 2008, through June 4, 2017. Patients that had diagnoses or medications associated with extremely high or low body temperatures were excluded from the analysis.
Normal body temperatures ranged from 97.3 to 98.2 degrees Fahrenheit, and the overall average was 97.9 degrees Fahrenheit.
Researchers also found normal body temperature varies from person to person based on physical characteristics and can fluctuate throughout the day. Statistical modeling revealed temperatures decreased with age and height but increased with weight. Time of day had the most influence on body temperature — patients' temperatures were lowest in the morning and highest around 4 p.m.
"Most people, including many doctors, still think that everyone's normal temperature is 98.6 F. In fact what's normal depends on the person and the situation, and it's rarely as high as 98.6 F," study author Julie Parsonnet, MD, the George DeForest Barnett Professor in Medicine and professor of epidemiology and population health at Stanford Medicine, said in a news release.