Klotho and healthy aging: what the research says

Klotho has become a familiar name in conversations about aging, but the research is often described more confidently than it can support. The clearest starting point is more specific: α-Klotho is a protein with an established role in kidney signaling and mineral balance. Animal experiments and human studies have raised broader aging questions, but they do not show that changing Klotho makes people live longer.

What is Klotho?

KL is the name of a human gene, a stretch of DNA that carries instructions for making a protein. It makes α-Klotho (alpha-Klotho), a protein found especially in the kidney. α-Klotho is sometimes shortened to “Klotho” in papers. It is related to β-Klotho (beta-Klotho), but the two are distinct proteins made from different genes; a finding about one should not automatically be applied to the other.

Some α-Klotho sits in a cell’s outer membrane, like a part of a receptor at the cell surface. A portion can be cut free and circulate in blood; this is called soluble Klotho. The kidney is a major source of that circulating form. “Soluble” describes where the protein is found, not a separate supplement or a proven measure of how fast someone is aging. A clinical review describes both forms and their roles in kidney signaling (Neyra, Hu, and Moe, 2021).

An established role in kidney mineral balance

One well-described job of membrane-bound α-Klotho is to help the hormone fibroblast growth factor 23 (FGF23) signal in the kidney. FGF23 is made mainly by bone cells. Klotho helps FGF23 connect with its receptor on kidney cells, which helps regulate how much phosphate the kidneys return to the blood or remove into urine. Phosphate is a mineral needed for bones and many cell functions; too much or too little can disrupt normal physiology. A 2024 kidney-focused perspective describes this FGF23–Klotho role and why it has drawn interest in kidney research (Yanucil and Faul, 2024).

This is a mechanism: a proposed or established sequence explaining how a biological effect happens. Knowing a mechanism can help researchers ask useful questions, but it does not by itself prove that changing the pathway will improve health or lengthen life.

Why animal aging studies drew attention

In 1997, researchers reported that mice with a disrupted klotho gene developed several problems that resembled aspects of aging and had shortened lives (Kuro-o et al., 1997). In 2005, a separate experiment reported longer lifespans in genetically modified mice that overproduced Klotho (Kurosu et al., 2005).

These were important animal findings, not demonstrations in people. A mouse model can help isolate a gene or pathway under controlled conditions; it cannot reproduce the full mix of genetics, health conditions, environment, and care that shapes human aging. Even a lifespan effect in a particular mouse strain does not establish a safe or effective Klotho treatment for humans.

What human studies suggest—and what they cannot show

Researchers have measured soluble α-Klotho in people and looked for links with health outcomes. An association means two things vary together in a study; it does not show that one caused the other. For example, a 2024 analysis linked U.S. survey data from 13,749 adults to later mortality records and reported a nonlinear, U-shaped association between measured α-Klotho and all-cause mortality. In a U-shaped pattern, the statistical relationship differs across lower and higher values rather than following one simple line (Sadr et al., 2024).

This observational analysis cannot establish that Klotho levels caused the outcomes or that changing a level would change risk. Health, kidney function, age, and other factors may affect both a blood measurement and later outcomes. The participants were adults of different ages, not a study designed to answer questions specifically about midlife women or menopause. A reported association in that population is not a personal prediction.

There is also a measurement problem. In a study of human samples that included people with different levels of kidney function, two laboratory methods for measuring soluble Klotho did not perform equally; sample handling also mattered (Neyra et al., 2019/2020). This makes a single blood value difficult to interpret as a universal benchmark. Klotho is not a validated personal “biological age” score.

Healthspan is not the same as lifespan

Lifespan is how long a person lives. Healthspan means the time spent in good health or with physical and cognitive function. These are related questions, but evidence for a change in one does not automatically prove a change in the other. A blood association, a pathway mechanism, or an animal lifespan result cannot stand in for a human trial measuring a meaningful health outcome.

What is known, and what remains open

• Established: α-Klotho is part of FGF23 signaling in the kidney and helps regulate phosphate balance.
• Early or uncertain: animal experiments and observational human findings motivate study of Klotho in aging and disease, but they do not establish what would happen if Klotho were changed in people.
• Not established: no Klotho intervention has been proven to extend human lifespan or to prevent or treat disease. Research into possible therapies remains at an early stage.

A Klotho result is therefore best read as a research measure, not a diagnosis, treatment target, or forecast. The evidence does not support midlife-specific claims for women from studies that were not designed to study them.