How long can you survive without gravity?

Weightlessness is not acutely dangerous, but the body reads it as an instruction to stop maintaining things it no longer needs. Fluid shifts headward in the first days, producing puffy faces, congestion and, over months, changes to the shape of the eyeball that can blur vision. Weight-bearing bone loses roughly 1 to 1.5 per cent of its mass per month without countermeasures, concentrated in the hip and spine, and postural muscle wastes alongside it. Crews on the International Space Station spend around two hours a day on resistive and aerobic exercise specifically to hold that at bay, and it works well enough that the practical limit is now radiation exposure and supply rather than physiology. The longest single spaceflight remains Valeri Polyakov's 437 days aboard Mir.

What happens, in order

Physiology, not instruction. Every figure here is a population range under particular conditions, and individual variation is large — temperature, exertion, fitness and health move all of them substantially. Nothing on this page is medical advice.

Going without something

• How long can you survive without water? About three days in mild conditions — but under a day in desert heat, and up to a week at rest in the cold.
• How long can you survive without food? Weeks rather than days — one to three weeks is typical, and water runs out long before calories do.
• How long can you survive without air? Consciousness goes in about a minute and brain injury begins around four to six minutes.
• How long can you survive without sleep? No one has died of sleep deprivation alone; the record is 11 days, and severe impairment arrives within two.
• How long can you survive without food and water? About three days — water sets the limit and food barely enters into it.
• How long can you survive without sunlight? Indefinitely, provided vitamin D comes from food or a supplement — sunlight itself is not a requirement.
• How long can you survive without human contact? Indefinitely in the direct sense — but isolation measurably raises the risk of dying early.
• How long can you survive without salt? Weeks to months at rest — kidneys are very good at conserving sodium — but days if you are sweating heavily.
• How long can you survive without vitamin C? Scurvy appears after roughly one to three months of near-zero intake, and is fatal in a few months more.
• How long can you survive without protein? Months, because the body cannibalises its own muscle — which is exactly why it eventually kills you.
• How long can someone with type 1 diabetes survive without insulin? Days. Missing insulin in type 1 diabetes is an emergency, not an inconvenience.