This is why returning astronaut Sunita Williams' hair turned white

Bone loss: NASA estimates astronauts lose up to 1% of bone density monthly in microgravity. Over 288 days, Williams may have lost nearly 10%, primarily in weight-bearing bones like the legs, pelvis and spine — significantly raising fracture risks.

“Without gravity, bones aren’t stressed, so the body breaks them down rapidly,” Schenker explained. “Young astronauts lose as much bone in a month as elderly people do in a year on Earth.”

Muscle atrophy: Despite exercising 2.5 hours daily, Williams appeared frail post-landing. NASA reports astronauts lose up to 10% of muscle mass on long missions, particularly in legs, back and core muscles. “Muscles ‘disintegrate’ without constant Earth-like resistance,” Schenker said.

Cardiovascular risks: Microgravity redistributes fluids evenly, weakening the heart’s pumping strength. Over time, this may cause heart muscle degeneration. “If a child were born in space, their heart might be too small to function on Earth,” Schenker noted.

Balance and vision issues: Returning astronauts often struggle with dizziness and coordination as their inner ear recalibrates to gravity. Williams also experienced Spaceflight Associated Neuro-Ocular Syndrome (SANS), altering her eye structure and vision.

Space radiation poses severe genetic risks. Astronauts on extended missions face DNA damage comparable to “smoking a pack of cigarettes daily,” said NASA nutritionist Dr. Scott Smith. Studies show increased chromosome alterations and cellular aging, akin to findings in NASA’s Twin Study, where astronaut Scott Kelly’s telomeres shortened during a year in space.

“Ionizing radiation shreds DNA strands, accelerating cell death and aging,” Schenker said. “Even skin cells age faster.” Williams’ hair whitening may stem from metabolic imbalances and limited hygiene options — astronauts clean hair with towels, not showers.

Williams, who ran a marathon aboard the ISS in 2007, now undergoes daily 2.5-hour resistance training, calcium-rich diets and balance therapy. Full recovery may take months, with some bone damage likely irreversible.

Psychological challenges loom large. “Isolation in space breeds profound loneliness,” Schenker said. “What astronauts miss most isn’t gravity or fresh food — it’s their families.” NASA provides psychological support for years post-mission to address reintegration stress and the “Overview Effect,” an existential shift some astronauts experience.

While NASA confirmed Williams returned in “good health,” the long-term impacts of radiation and cellular damage remain unclear. “The body can heal but some changes, like immune decline or neurological harm, may persist,” Schenker cautioned.