Lettuce grown in chambers onboard the International Space Station (ISS) is safe to eat, NASA has concluded, six years after astronauts began growing and eating the crops.
Astronaut Steve Swanson harvests some of the lettuce crop in June 2014 (Photo: NASA)
Astronauts first grew red romaine lettuce from surface-sterilised seeds within specialised growth units equipped with LED lights and a watering system between 2014 and 2016, which grew undisturbed for up to 56 days.
Crew members ate part of the mature leaves before the remaining crop was deep frozen in preparation for being sent back to Earth for chemical and biological analysis.
Following extensive testing, a new study published in journal Frontiers in Plant Science confirmed the space-grown lettuce was safe to eat, paving the way for future crop, fruit and vegetable growth in microgravity during long missions.
Providing astronauts with fresh but safe food while in space has been a key challenge for NASA for decades: the organisation has been experimenting with plant growth onboard the ISS since 2002.
Crew members usually eat processed pre-packaged rations of chicken, beef, peanut butter, shrimp cocktails, fruits, nuts and chocolate that's been sterilised through heat, freeze drying or irradiation to ensure their longevity.
Scientists back on Earth recreated the same conditions as on the ISS in terms of temperature, carbon dioxide and humidity to grow control plants for testing.
The control plants were similar in composition to the space-grown lettuce, but some tests revealed that the space-grown leaves tended to be richer in potassium, sodium, phosphorus, sulphur and zinc, alongside phenolics - molecules with proven antiviral, anticancer, and anti-inflammatory activity.
Both sets of lettuce had similar levels of anthocyanin and other antioxidants, compounds which protect your body by fighting free radicals.