Prolonged Exposure of the Head to Strong Sunlight Impairs Motor-Cognitive Performance
Wed, April 14, 2021

Prolonged Exposure of the Head to Strong Sunlight Impairs Motor-Cognitive Performance



Performance and health impairments provoked by thermal stress are some of the societal challenges that are intensifying and spreading with global warming. However, science may still be underestimating its true impact because no study has evaluated the effects of prolonged direct sunlight exposure on human brain function and temperature.


Effects of direct sunlight exposure to the head

In a new study conducted by Jacob F. Piil from the University of Copenhagen's Department of Nutrition, Exercise and Sports and colleagues, they suggest that prolonged exposure of the head to strong sunlight impairs the motor-cognitive performance of the person. The findings may have important implications for work productivity and safety.

According to the team, approximately 50% of the world population lives in regions where heat stress affects their ability to live productive and healthy lives. Working in a hot environment is also linked to hyperthermia, which is a group of heat-related conditions characterized by abnormally high body temperature. The condition happens when the heat regulation system of the body becomes overwhelmed by the outside factors, causing an increase in a person’s internal temperature. Working in the sun also impairs the ability to perform manual work that is physically demanding.

The University of Copenhagen's study provides evidence that direct exposure to the sun, especially to the head, impairs the cognitive and motor performance of a person. Professor Lars Nybo, who co-authored the study, said via Science Daily that they observed the decline in cognitive and motor performance at 38.5 degrees, which is 1-degree lower body temperature than past studies have established. He said this is already a “substantial difference.”

They said that many workers in transport, construction, and agriculture are at risk of being exposed to strong sunlight and it can affect their productivity and safety, not just their health.

Associate professor Andreas D. Flouris also shared that there is a need to adapt to a solution that will prevent the negative effects of direct sunlight exposure while working. For instance, people undertaking daily work outside should protect their head against the sun. We must also mitigate the performance and health impairments caused by thermal stress. The co-author considers it relevant for traffic and work safety as well as to lessen the risk of making mistakes while working outdoors.



Impaired scores for motor-cognitive tasks

Human brain function is highly dependent on a stable supply of oxygen and blood glucose but is also highly vulnerable to changes in the ability to maintain the cerebral heat balance, they added. This kind of vulnerability stems from the increased metabolic heat production of the brain, being highly insulated because of its enclosure in the cranium – the top portion of the skull that protects the brain.

They went on to say that impaired scores for motor-cognitive, complex motor, and simple tasks suggest that prolonged exposure of the head to sunlight has considerable consequences for performance.


The overall design of the study

Eight healthy and active males aged 27 to 41 participated in the study. The team conducted a motor-cognitive test on them consisting of four different logical and computer math tasks that relied on their fine motor precision. All participants completed two sessions on two different occasions in the environmental chamber at the University of Copenhagen.  Four lamps were also used to radiate the head (sides, back, and top to avoid blinding the participants) and on their lower body.  The motor cognitive testing was done three times in each session. Prolonged exposure to the radiant heat during the test lasted for two hours until the core temperature increased by 1 degree above the baseline. They were also exposed to no radiation or acute exposure after 15 minutes of simulated sunlight exposure.

Before they started with the experimental sessions, all participants were familiarized with the experimental procedures to be conducted, such as EEG measurements, cognitive testing, and the radiant heat exposure from the lamps. The purpose of this is to avoid significant learning effects in the motor-cognitive protocol during the actual test as it may obscure the result. All study participants also arrived at the laboratory 30 to 45 minutes before the beginning of the experiment during the two sessions. They also emptied their bladders into a sealed urine container and the individual urine samples were analyzed by the team for urine specific gravity.

The team said that in terms of ecological outdoor settings, their findings will be relevant for the billions of people who are living in areas with seasonal and permanent heat stress, including high levels of solar radiation that are not currently included in weather analyses.



Outdoor workers and sun exposure

UK’s Health and Safety Executive (HSE) also advised that when sunlight is intense for outdoor workers, it is sensible to protect themselves by keeping their top on, wearing a hat with a flap that covers the back of the neck and the ears, drinking plenty of water to avoid dehydration, using a high factor sunscreen of at least SPF15 on any exposed skin, staying in the shade whenever possible, such as during lunchtime and breaks, and checking the skin regularly for unusual spots or moles.

In the US, the jobs that were likely to require outdoor work were construction and extraction (95.1%), protective service (91.4%), installation, maintenance, and repair (87.3%), building and grounds cleaning and maintenance (77.0%), personal care and service (73.9%), transportation and material moving (72.9%), education, training, and library (64.2%), community and social service (58.1%),  management (56.1%), and architecture and engineering (55.9%).

On the other hand, the jobs that are least likely to require work outside were those in production (17.4%), office and administrative support (18.7%), computer and mathematical (20.9%), healthcare practitioners and technical (23.4%), business and financial operations (36.5%), healthcare support (39.8%), food preparation and serving related (40.7%), and sales related (42.1%), according to the US Department of Labor.

Overall, 70.8% of US adults use at least some form of sun protection, such as protective clothing, sunscreen, and shade, according to the CDC. 

While the sun offers our body plenty of good things such as increased vitamin D, improved mood, stronger bones, higher quality of sleep, and lower blood pressure, there are also risks of getting too much sun. These risks go beyond the skin. As the present study demonstrates, prolonged exposure of the neck and head can impair performance in various tasks that rely on the combined motor and cognitive functions.