The Boston Marathon: One of the world’s best-known road races held annually on Patriots’ Day is hosted by several cities in a point-to-point fashion and finishes in Boston. The race was first run in 1897. It’s now the world’s oldest annual marathon. Despite its meagre 15 participants in 1897, it now attracts around 30,000 participants and around 500,000 spectators yearly.

The marathon is a long-distance race with a distance of 42.195 km (26.2 miles). Despite being  one of the original modern Olympic events in 1896, the distance did not become standardized until 1921.

The current men's world record time is 2 hours, 1 minute and 39 seconds. It was set in the Berlin Marathon by Eliud Kipchoge on September 16th, 2018, an improvement of 1 minute 18 seconds over the previous record also set in the Berlin Marathon by Dennis Kipruto Kimetto, of Kenya on September 28, 2014. The women’s world record was set by Brigid Kosgei of Kenya in the Chicago Marathon on October 13, 2019, in 2 hours, 14 minutes and 4 seconds.

In 1923, coincidentally, at the Boston Marathon, Samuel A. Levin, a famous American cardiologist and Harvard professor, was one of the first scientists to draw attention to glucose measurement during exercise. The results of such a very early investigation were published a year later in the Journal of the American Medical Association (JAMA), one of the first studies that revealed the impact and the relevance of monitoring glucose levels during exercise.

The cover of the famous paper from Samuel A. Levin published in JAMA in 1924.

Levine and colleagues studied a group of 11 runners with the aim to see what changes occurred in some of the more important constituents of blood. This included sugar and uric acid (the “sugar” they were referring to was glucose) after the 1924 Boston marathon. Measurements were made right before and right after the marathon (within 2 minutes was reported) and changes were associated with performance (time to complete the marathon), individual feeling, and perception of effort.

In the table below are charted the data obtained from the study.

Glucose data from the 1924 Boston Marathon.

Here’s what Levin noticed:

“The most striking feature of the study was the marked fall in the sugar content of the blood that occurred in a majority of the runners. An analysis of the individual findings proves rather illuminating.”

The table here shows an interesting association between the “sugar level” at the end of the marathon and the “physical condition” of the runners reported by the researchers at the finish line. All those who had a glucose level <70 mg/dL at the end of the race were declared as in “Poor” or “Very Poor” condition afterward. Symptoms of pallor, irritability, shock, unconsciousness and dizziness (classic of hypoglycemia) were also interestingly reported in those with very low glucose levels (<50 mg/dL). One of those (participant #37 with a glucose level of 45 mg/dL at the end of the marathon) was reportedly “unconscious and brought in by the police, perfectly limp.”

Those who had normal glucose showed no symptoms or signs of shock. On the contrary, the participants that finished the race with higher glucose levels felt and performed better. The winner of the race (runner number 1 in the table) broke the world record at that time and was one of those with the higher glucose level at the start of the race and was in excellent condition at the end.

Interestingly, those with the higher glucose level at the end of the marathon ingested some food (bread, meat, and soda water) either before or along the course of the race. For the first time, we saw the close association between carbohydrate intake and glucose levels during a field experiment.

The main result?

“The significance of the foregoing data is that, during such a prolonged and violent effort as a marathon race, when the metabolism is more than ten times the normal, the normal supply of the reserve blood sugar in the body is insufficient.”

And also:

“There was also a close correlation between the condition of the runner at the finish of the race and the level of his blood sugar.”

The beauty and relevance of such a very early study lies in being one of the first research reports that highlighted the key role of glucose control in supporting human performance during exercise. With such information, 100 more years of research has been conducted to highlight the importance of carbohydrates feeding during endurance training and racing. Now, thanks to accessible CGM technology for sports, it would also be possible to visualize the impact of carbohydrate intake over what seemed to matter the most 100 years ago: glucose control.

There’s so much more to learn in this science. And we’re honored to be pioneering these insights.

Interested in your own glucose levels? Supersapiens offers a window into your body. Come track your own glucose levels at


  1. Levine Sa, Gordon B, Derick Cl. Some Changes In The Chemical Constituents Of The Blood Following A Marathon Race: With Special Reference To The Development Of Hypoglycemia. Jama. 1924;82(22):1778–1779. Doi:10.1001/Jama.1924.02650480034015