Warning signs your body is low on ferritin as Bryan Johnson reveals he's been deficient for over a decade

Bryan Johnson has revealed that he is battling an autoimmune disease, and there are some key warning signs your body may show that could indicate similar health issues.

The biohacker is known for his extreme methods to increase his life expectancy, spending millions of dollars each year and becoming the world’s most measured man in history.

In a post on social media, Johnson shared details about his new diagnosis, revealing that he has had low ferritin for the past 11 years.

In the statement, the venture capitalist explained how, ‘on the surface’, his low ferritin levels were ‘easy to dismiss’ but it ultimately caught up with him.

Key warning signs that your body is low on ferritin

There are some warning signs that others can look out for to indicate if their body is also low on ferritin.

Ferritin is the protein which stores iron in your cells and, when levels in the body are low, you might experience side effects such as extreme fatigue, pale skin, dizziness, shortness of breath, and it can eventually lead to iron deficiency anemia.

Common warning signs include: dermatological changes, neurological and sensory changes, cardiorespiratory strain, pica, fatigue and weakness.

In his tweet, Johnson explained: “Ferritin measures stored iron, while hemoglobin measures circulating iron, and because the body drains its reserves first to keep hemoglobin normal, you can be fully iron deficient with a perfectly normal hemoglobin and hematocrit. This is why my low ferritin kept getting dismissed: the numbers that define anemia looked fine, so no one asked why my iron reserves wouldn't refill.”

Bad news #1:

I have an autoimmune disease. My stomach is eating itself.

Bad news #2:

2–5% of people have this, too. Likely more, because it hides.

Good news:

I'm going to try and solve it. Will share all.

As a kid, I ate sugar cereal, drank sugary soda, and gobbled down… pic.twitter.com/EbJ8a916uS

— Bryan Johnson (@bryan_johnson) June 30, 2026

After being diagnosed with an autoimmune disease known as Autoimmune Gastritis (AIG), earlier this year, he discovered that this condition causes ‘irreversible damage: nutritional deficiency, anemia, and over a long horizon, elevated cancer risk’.

Bryan Johnson has been diagnosed with an autoimmune disease

Johnson continued: “My team pressed on that question. They first turned to a colonoscopy. I was 48 years old and overdue. It was good health hygiene to have while also serving a specific purpose of searching for a hidden source of blood loss such as a polyp or even cancer in my bowels. Either one of those would be an explanation of why the iron kept disappearing.

“At the same time, they began connecting the dots. Iron absorption depends on stomach acid, so one theory was that my stomach acid was disrupted. They also knew that thyroid and stomach autoimmunity often travel together, so often that the pairing has a name: thyrogastric syndrome.”