It comes as part of the build-up to Tokyo 2020 where races are expected to take place in warm weather.

Organisers have already moved the start of the men's and women's events to 6.30am in the hope of cooler conditions.

However, the temperature was nearly 30 degrees by 6am at the Olympic test event in August, according to the Japan Times.

France's Cassandre Beaugrand was treated in hospital for heatstroke and the run section of the women's race was halved from 10 kilometres to five.

Fears over heat prompted a decision to move the Tokyo 2020 marathons to Sapporo, 800 kilometres to the north of the capital.

Triathlon, however, is remaining in the city with a course around Odaiba Marine Park.

Beat the Heat has been released in cooperation with Australia's University of Canberra and Britain's Loughborough University. 

Topics covered include heat acclimation, core temperature, cooling strategies and how much an athlete should drink.

The ITU rules to mitigate heat stress are also covered.

"We in ITU have always put the athletes' health and safety first, and this comprehensive document is a clear example of the commitment of our team, the sport department and the Medical Committee in ITU, in guaranteeing that all triathletes and Paratriathletes can perform at their best conditions and do it with all the safety measures that we can provide them," said ITU President Marisol Casado, an International Olympic Committee member.

The ITU said that their document is the first heat advice from a sporting organisation which also covers Para-athletes specifically. 

"The sport and medical team in ITU is fully committed to guarantee the safety of all the athletes," said Thanos Nikopoulos, the ITU's head of operations and one of the authors of the study. 

"After analysing the impact of the heat and humid conditions in the test event held in Tokyo in the summer of 2019, and after establishing a working group with representatives from our Athletes, Technical, Medical and Coaches' Committees along with a number of experts on this field, we decided to elaborate these guidelines to try to help all athletes on their road to Tokyo 2020 and beyond."

The Tokyo 2020 Olympics will take place between July 24 and August 9.

More than 50 deaths were recorded in Japan because of the heat in July of last year.

"Beat the Heat is the ultimate publication for triathletes and Paratriathletes," said ITU Medical Committee chairman Sergio Migliorini.

"We have gathered all the scientific and medical information available to make it easy to comprehend for athletes and coaches, in order to facilitate their performance, training and acclimation."

The guidelines can be viewed here.