Heat sensitivity is a considerable problem for people with MS, with the majority experiencing worsening of their symptoms when their body temperature increases – even if this is just by a small amount. One symptom that can be most exacerbated by heat is fatigue, which can limit the ability to exercise and carry out day to day tasks.

Why people with MS experience heat sensitivity is still unclear. It is thought that a rise in core body temperature of about 0.5 ˚C may slow or block signals travelling along nerves that have already been damaged or demyelinated. This is known as Uhtoff’s phenomenon – named after Wilhelm Uhthoff, who first described it in the 1890s.

Physical activity and exercise are very important for people with MS to manage their MS and to improve overall health and fitness. So, scientists around the world are working on the best strategies to help people with MS manage heat sensitivity.

Many, such as wearing cooling vests containing ice or submerging the lower half of the body in cold water before exercise, may not always be practical.

A team of Australian researchers, led by Dr Ollie Jay of the University of Sydney, has published new research in the scientific journal Medicine & Science in Sports & Exercise into the efficacy of a simple strategy to reduce heat sensitivity during exercise: drinking cold water.

Cycling test

In this study, the scientists recruited 20 people: 10 with MS and 10 without MS. The participants were asked to cycle on a stationary bicycle in a controlled atmosphere set at 30°C and 30% humidity on three separate occasions. They had to cycle either until exhaustion, or for a maximum of 60 minutes. The participants were given a drink of water of 3.2ml per kilogram of body weight every 15 minutes. The water was either cold water (1.5 degrees) or warm water (37 degrees).

The control group who didn’t have MS all managed to complete 60 minutes cycling, whereas only 3 of the 10 people with MS could manage the full 60 mins at 30°C when given warm water. However, when the people with MS were given cold water to drink, five of the ten managed the full 60 minutes of cycling, whilst those who couldn’t make the full 60 minutes did manage to cycle for approximately 30% longer.

During the activity, the scientists also measured core body temperature, skin temperature, and heart rate. Surprisingly, given the effects it had on exercise duration and the perception of fatigue, the cold water had no impact on heart rate, core body temperature, or skin temperature.

The research team suggests that it may be the temperature sensors in the mouth, digestive tract, and abdomen that could be playing a role in signalling to the brain to affect the perception of fatigue, rather than the cold water acting via a change in core body temperature.

The researchers are now planning to investigate this fascinating finding in more depth. Practically, it is possible that, since most of the temperature sensors are in the mouth and on the tongue, merely swilling cold water in the mouth without swallowing may reduce heat sensitivity in people with MS and the team will investigate this possibility further.
These fascinating and unexpected results may change the way we think about heat sensitivity and the way it can be managed in people with MS.

With thanks to MS Research Australia – the lead provider of research summaries on our website.