Contrary to long-held dictum, the average person's normal peak body temperature apparently is not 98.6 degrees Fahrenheit, researchers reported Tuesday.
The true normal average top body temperature for an adult is 99.9, according to a new study in the Journal of the American Medical Association."In view of the data presented, we believe that (98.6) should be abandoned as a concept having any particular significance for the normal body temperature," wrote Dr. Philip Mackowiak of the Veterans Affairs Medical Center in Baltimore and his colleagues in reporting the findings.
The traditional 98.6 reading should be replaced by 98.9 in the early morning and 99.9 overall as the upper limit of normal oral temperature in healthy adults age 40 or younger, they said.
"In our study population, (98.6) was not the overall mean temperature, the mean temperature of any of the time periods studied, the median temperature, or the single most frequent temperature recorded," they said.
"The source of confusion over what constitutes the upper limit of the normal body temperature, we believe, derives from individual variability that limits the application of mean values derived from population studies to individual subjects and from the fact that the maximum oral temperature, exhibited by any population, varies according to time of day," they said.
Mackowiak and his colleagues collected 700 oral temperature readings from 122 men and 26 women at 6 a.m., 8 a.m., noon, 4 p.m. 6 p.m. or midnight. The subjects were asked not to eat, drink or smoke for 15 minutes before each reading.
The temperatures ranged from 96 to 100.8, with the overall mean temperature being 98.2, plus or minus 0.7, the researchers said.
The average temperature varied, depending on the time of day, from a low of 97.6 at 6 a.m. to a high of 98.5 at 4 p.m. and 6 p.m., they said.
But a temperature of 98.6 accounted for only 8 percent of the readings, they said.
Women had slightly higher average temperatures than men - 98.4 versus 98.1, and blacks tended to have slightly higher temperatures than whites - 98.2 versus 98.1, they said.