What a long-haul flight does to your body
Thin air, dry air, still legs and a confused body clock, and what helps with each.
A long-haul flight is a strange experience for your body. For ten or twelve hours, you sit still in thin, dry air at the equivalent of a mountain altitude, eating at odd times and crossing time zones faster than your body clock can follow. Most people arrive tired and a bit swollen, and a few days later they feel normal again. Here is what is happening, and what helps.
Thin air
Aircraft cabins are pressurised, but not to sea level. The pressure inside is usually similar to being at 1,800 to 2,400 metres above sea level. Your blood carries a little less oxygen than normal. Healthy people rarely notice, apart from feeling more tired, but it is why alcohol can feel stronger in the air.
The pressure change also affects gas in your body. Your ears pop on the way up and down, and gas in your stomach expands, which is why some people feel bloated.
Dry air
Cabin air is very dry, often much drier than a desert. Your skin, eyes and throat lose moisture, and you may wake with a sore throat or tired eyes. Drinking water regularly helps. Coffee and alcohol are fine in moderation, but they do not replace water.
The cabin is a desert at altitude. Treat it that way.
Daniel Osei
Sitting still
Hours of sitting slow the blood flow in your legs. Your feet and ankles swell, and for a small number of people, the risk of blood clots rises. Moving regularly makes a difference: walk the aisle when you can, and flex your ankles and calves in your seat every half hour.
Jet lag
Jet lag happens because your body clock is still on home time. It usually takes about a day per time zone to adjust, and flying east is harder than flying west. Light is the strongest signal: get daylight in the morning at your destination if you flew east, and in the evening if you flew west.
| What helps | When |
|---|---|
| Water | All flight |
| Walking the aisle | Every 1–2 hours |
| Daylight | First days after arrival |
| Local meal times | From arrival |
Who should take extra care
People with heart or lung conditions, recent surgery, pregnancy or a history of blood clots should talk to a doctor before a long flight. Compression socks help many people with swelling.
Before you fly
Preparation makes a difference. In the days before a long eastward flight, going to bed and getting up an hour earlier each day helps your body clock start to shift. Before a westward flight, do the opposite. Pack a water bottle to fill after security, a warm layer for the cold cabin and comfortable clothes that do not press on your waist or legs.
After you land
The first day matters most. Stay awake until a reasonable local bedtime, get outside in daylight and eat at local mealtimes. A short nap of less than thirty minutes can help you get through the afternoon, but a long sleep in the middle of the day will make the first night much harder.
Food and drink on board
What you eat matters less than you might think, but a few choices help. Light meals are easier to digest in the dry, low-pressure cabin. Salty food adds to swelling, and fizzy drinks add to bloating as the gas expands. Many experienced travellers eat lightly on board and have a proper meal at local mealtime when they arrive, which also helps the body clock adjust.
If you need to sleep, an eye mask, earplugs or noise-cancelling headphones and a neck pillow make more difference than any pill. Sleeping tablets should only be taken with medical advice.
