What Happens When You Endure An 18.5 Hour Long Flight?

Eve Simmons turns herself into a test subject to see what happens on board a 18.5 hour direct flight, wearing an assortment of wearable health trackers to measure her heart rate, blood oxygen levels, blood pressure, as well as her brain waves to monitor her stress and alertness.

She was armed with a glucose monitor and tests to check her reaction times to see how the flight affected her ability to think clearly, as well as a device to measure ankle circumference to check for swelling which is a sign of sluggish circulation. 

She also brought a pollution monitor to continuously monitor the quality of air around her, as she was concerned about harmful pollutant in reports that are linked to asthma and chest infections could be in the cabin air:

Tristan Loraine, a former British Airways captain who campaigns for cleaner air on planes, says: “The air you breathe in on most aircraft is compressed via the engine. So it becomes contaminated with toxic compounds in engine oils.”

Terry Tetley, Professor of Lung Cell Biology at Imperial College London, says: “The heating of engine fuel emits tiny, toxic substances – known as ultra-fine particles – and other chemicals which penetrate deep within the sensitive lung lining and are taken up by the bloodstream. They cause inflammation of the lungs and increase the risk of some cancers.”

Microscopic toxic compounds have been topic of debate in several reports. A detector was recently used by Loraine aboard several flights which were suggested to have cabin air that contained over 100 times the amount outside of traffic congested Victoria Underground Station in London. Several companies have tried to improve cabin air quality, but this may only be fighting half the issue. 

Dr Susan Michaelis, an aviation safety researcher from the University of Stirling says, “Air is only filtered the second time it enters the cabin, so the toxic particles have already made their way around the cabin once,” she says. “Ultra-fine vapours, emitted when fuel is burned, are in the air at the airport, and this can enter the cabin before take-off.”

Apon board the plane the pollutant detector was in the green, almost 0 toxic compounds found, levels climbed steadily after take off, and peaked halfway through the flight in a red circle which is a significant warning about high levels of pollution being in the cabin air. The levels did fall some after leveling out, but remained moderately high. 

Prof Tetley says: “Exposure like this might trigger temporary inflammation and irritation on the airways and lungs. But it is chronic exposure that causes damage to the body’s cells, increasing the risk of cancers and lung infections.”

A detector picked up alarmingly high levels of radioactive gas radon at 100 times higher than levels in central London. Radon is found in cigarette smoke as well as being emitted from certain rock, it is a known cancer risk with exposure over long periods, and over long flights which tend to fly at higher altitude radon is a big concern. 

Professor Michael Lockwood, Professor of Space Environment Physics from the University of Reading, says: “We’re very concerned about radioactive particles in the atmosphere at extremely high altitudes. These high-energy particles break off from rays outside the solar system and enter the cabin air supply. They attack human cells and are known to cause cancers of the skin and lungs. While it is unlikely to cause harm in a single flight, it’s a concern for frequent flyers. Roughly 12 return flights to the US from the UK gives the same radiation dose as a CT scan – so roughly 200 X-rays. That would be roughly your safe radiation allowance for the entire year.”

Flying can also cause other health effects by disrupting the internal clock patterns which determine our sleep and wake cycle which are largely governed by light. Natural light triggers an alert response which kick starts the cardiovascular system, brain, and metabolism into action; as darkness sets in hormones are released that slows down bodily processes. Disruptions can affect anything from digestion, immunity, and cardiovascular health. 

Preflight Simmons had a resting heart rate of 49 beats per minute. After take off this increased to 60, which may be partially due to stress, and her blood pressure increased by 10%. Three hours into the flight, her heart rate reached 65 beats per minute where it remained even with the lights dimmed to simulate the evening. 

Prof Foster says: “Your body was in day mode and fighting the chemicals emitted in response to dark to make you feel sleepy.” Foster also says that stressful experiences can also cause a fluctuation in heart rate throughout the day.

Halfway into the flight, her heart rate returned to 49, despite being awake for 14 hours and being incredibly tired. When the flight reached New York, at the time when she would normally awake, her heart rate went up to 53. When the plane was landing it went to 60 beats per minute, and her blood pressure suddenly increased after remained stable throughout the flight higher than normal.

Prof Foster says: “Fluctuating heart rate and blood pressure is a risk for people with pre-existing heart conditions or those who must take medication in accordance with body clocks. It could put vulnerable people at higher risk of stroke.”

Flying increases the risk of developing a fatal blood clot in the lower leg called deep vein thrombosis, symptoms of sluggish circulation can include swollen ankles as fluid collects in the lower limbs. 

Professor Mark Whiteley says: “DVT isn’t only a result of sitting down for a long time. Reduced oxygen causes fewer anti-clotting proteins to be produced. A lack of moisture in the cabin dehydrates blood, making it even thicker. Combine this with the lack of movement and it’s the perfect storm for a blood clot.”

During the flight there was no change in her ankle width, but her blood oxygen monitor showed gradually depleting levels which had dropped almost 10% four hours into the flight, and gradually stabilised towards the end of the flight at 95%. Her fasting blood sugar increased to 5.3 from 4.7 on board, increasing slightly after eating then returning.

GP doctor Ellie Cannon was dubious about the results. “With a reading of 90 you’d be having an asthma attack or fainting. I suspect you were either very cold or there was a problem with the machine.”

Prof Foster says: “At night the body is less able to clear sugar from your blood because the metabolism slows down in preparation for sleeping. In the morning, our cells convert food to energy much more efficiently. If you’re eating when the body is programmed to be sleeping, it won’t process the food effectively, causing more dramatic spikes and drops in blood sugar,” warns Prof Foster. “Over time, this increases the risk of obesity and type 2 diabetes.”

“Exercise can help the body to burn up excess glucose,” says Prof Foster. “And on a plane you’re just sitting in one position. Your body clock thinks it’s the evening and releases hunger hormones,” explains Prof Foster. “It can take up to two weeks for your metabolism to adjust,” Prof Foster says. “These spikes can be risky if you’re on the cusp of type 2 diabetes.”

Cortisol stress hormones naturally increase during the day and decrease in the evening, levels can also  peak in response to feelings of anxiety or stress to trigger the fight or flight response. “Brain areas involved in learning, memory and emotions are impaired at night,” says Prof Foster. “At 4am, our brain capacity is akin to that of being legally drunk.”

Simmon’s headband detected changes every hour, before take off brain activity was calm, within an hour of take off stress response was active; and her reaction times began with 16 out of 22, this dropped to an end scoring of only 4. 

“It takes the brain and the rest of the body roughly two weeks for the clock to reset,” says Prof Foster. “Meanwhile, world leaders fly across the globe making crucial decisions while chronically jet-lagged. We need to start considering chronic jet lag as an international health problem.”

In a statement, Singapore Airlines said: “Airbus has demonstrated during extensive flight testing that the air quality on board the A350 meets all airworthiness requirements and international standards. Generally, medical conditions don’t stop you from flying. However, our passengers are encouraged to ensure that they are medically fit before flying with us.”