Bryan Johnson is known for trying unusual ways to slow down ageing. The American tech entrepreneur, who spends millions every year on health research, has now shared another detail from his personal experiments that has surprised many people.
In a post on X, Johnson revealed that he keeps a small sample of his girlfriend’s menstrual blood stored in a freezer at -80°C. He later explained that it is part of his ongoing research into health and longevity.
Why He Stores The Blood
Johnson wrote, “Kate’s period blood is in my -80 °C freezer,” referring to his girlfriend, Kate Tolo, a 30-year-old Australian-Bosnian biohacker. He added that he stores around 10 ml of her menstrual blood.
The post came just a day after Johnson publicly questioned whether he had “taken this whole longevity thing too far.”
After people reacted to his post, Johnson explained why he believes menstrual blood is useful for research. According to him, menstrual blood can reveal information that regular blood tests cannot because it comes directly from the uterus.
He said it can be studied to look for uterine cells, immune cells, stem cells, and harmful substances such as microplastics, PFAS (also known as “forever chemicals”), and endocrine-disrupting chemicals.
“Menstrual blood is valuable and underutilized,” he wrote. “We collected to look for diseased tissue, measure microplastics, measure endocrine disruptors, measure PFAS.”
He further explained, “It’s a non-invasive look into the uterus,” adding, “This is great because you get the data without surgical biopsy, it can be repeated every single cycle, and it measures the uterine environment directly instead of inferring it from a standard blood draw.”
Kate’s period blood is in my -80 °C freezer.
Around 10 mL. pic.twitter.com/OdLxO9qyJu
— Bryan Johnson (@bryan_johnson) July 31, 2026
Who Is Bryan Johnson?
Bryan Johnson is an American entrepreneur who founded the online payments company Braintree. The company was acquired by PayPal in 2013 for around $800 million.
Over the past few years, Johnson has become widely known for his efforts to slow ageing through a project called Blueprint. As part of that project, he follows a strict daily routine that includes a carefully planned plant-based diet, regular exercise, fixed sleeping hours, supplements and frequent medical tests.
He also tracks hundreds of health markers, undergoes regular scans and blood tests, and often shares the results of his experiments publicly as he continues exploring different ways to improve long-term health.