Thrombosis, jet lag, circulation 21 21 hours of sitting: This is how your body survives the long-haul flight

A new record-breaking flight will soon test the human body’s limits as Qantas prepares to launch its first direct service between London and Sydney, spanning 21 hours with no intermediate stops. The flight, set to begin in autumn 2027, will be the longest commercial non-stop journey ever offered, raising questions about how the human body copes with such extended periods in confined conditions. Experts from Zurich University's Centre for Travel Medicine have examined the physiological effects of this unprecedented travel duration, highlighting potential risks and offering practical advice for passengers. The flight presents similar challenges to existing long-haul journeys but extends them significantly. Factors such as lack of movement, dry cabin air, reduced oxygen levels, and close proximity to other passengers all persist over a much longer period. Modern HEPA filters reduce infection risk, but they do not eliminate it entirely. The most noticeable effect comes from the increased thrombosis risk: for each additional two hours of flight time, the risk rises by approximately 18 percent. While statistical data indicates that lost luggage occurs more frequently than deep vein thrombosis, about six per 1,000 checked bags compared to one per 4,600 passengers on average, the estimated risk for a 21-hour flight could reach roughly one in 1,300, though reliable data on such long flights does not yet exist. Movement is the key factor in preventing thrombosis, responsible for around 75 percent of cases. Passengers seated by the window tend to move less than those near the aisle, making aisle seats potentially beneficial. Standing up every two hours and performing seated calf muscle exercises can effectively lower the risk. Compression socks offer added protection for those with higher risk. Contrary to popular belief, aspirin does not provide sufficient prevention. Dry cabin air contributes to eye and nasal discomfort. Humidity levels inside aircraft range from 10 to 20 percent, comparable to conditions in the Atacama Desert, causing tears and mucus membranes to evaporate quickly. Preservative-free artificial tears applied before the flight prove most effective. Conscious blinking and using a screen positioned below eye level help mitigate these issues. Additionally, the airflow from overhead vents exacerbates dryness, which can be counteracted with moisturizing nasal sprays. Low oxygen levels in the cabin, maintained at a pressure equivalent to about 2,400 meters above sea level, lead to a noticeable drop in blood oxygen content. This mild altitude adjustment is generally well tolerated by healthy travelers. However, during simulated 20-hour flights, seven percent of participants developed symptoms resembling mild altitude sickness, including headaches, typically within three to nine hours of the flight. Preparation is crucial for managing the physical demands of such a long flight. Adjusting sleep schedules two to three days prior to the trip helps align with the destination's time zone. For eastbound flights, shifting the sleep schedule earlier by one to two hours is recommended, while westbound trips require delaying it accordingly. Caffeine intake should be limited during this period. During the flight, wearing loose, comfortable clothing facilitates movement. Alcohol consumption should be avoided due to its dehydrating effects and disruption of sleep. Staying hydrated is essential. Melatonin can be taken strategically: for eastbound flights, it should be consumed at bedtime upon arrival, while for westbound trips, it is best taken in the second half of the night. Dosages ranging from 0.5 to 1 mg are advised, with amounts exceeding 5 mg discouraged. After landing, adapting quickly to the local light and sleep cycle is vital. Exposure to natural light helps reset circadian rhythms, aiding recovery and reducing jet lag. Engaging in light physical activity and maintaining hydration continue to support overall well-being post-flight.