The internal clock of immune cells: Is the immune system younger in the morning?

As the immune system ages, it reacts more slowly to pathogens, vaccines become less effective, and the risk of cancer increases. At the same time, the immune system follows a 24-hour rhythm, as the number and activity of many immune cells fluctuate throughout the day.

Researchers  have now investigated whether this daily rhythm influences the aging of the immune system and whether the immune system behaves "younger" or "older" at certain times of the day.

For the new study published in Frontiers in Aging, researchers took blood samples from participants in the morning, at noon, and in the evening. Using the so-called "IMMune Age indeX (IMMAX)," they determined each individual's immune age and analyzed how it changed throughout the day.

The IMMAX is a biomarker determined by the ratio of certain immune cells in the blood. As part of biological age, it correlates with actual chronological age.

Individual immune cells that are relevant for calculating the IMMAX fluctuate throughout the day. For example, in the morning, researchers observed an increased frequency of natural killer cells (NK cells)—key protective cells that defend the body against infections and cancer. In contrast, other immune cell types showed the opposite pattern.

The circadian rhythm regulates immune system activity. Hormones, body temperature, nerve signals, and messenger molecules tell immune cells when to move or become active. This leads to daily fluctuations in the number of immune cells in the blood. However, these fluctuations do not appear to influence immune age over the course of the day, as the researchers discovered. Despite measurable daily differences, the IMMAX remained largely stable, as individual immune cell types apparently balance each other out.

The IMMAX is a biomarker for immune age that is largely independent of the time of day. Nevertheless, slight differences were observed depending on a person's chronotype—that is, whether they are more active early in the day ("larks") or late in the day ("owls"). For early risers ("larks"), the IMMAX value decreased slightly from morning to noon. This suggests that the time of blood sampling in relation to waking up is important.
"When we wake up in the morning and become active, this apparently influences the movement of our immune cells and thus has a slight effect on the IMMAX value.

In large cohort studies, the timing of sampling is less critical, as fluctuations are balanced out.

Sina Trebing et al, Influence of circadian rhythm on the determination of the IMMune age indeX (IMMAX), Frontiers in Aging (2025). DOI: 10.3389/fragi.2025.1716985

The study findings can help develop early-stage cancer prevention strategies.

Researchers have discovered why a specific mutation leads to tumorous growth in human lungs. The same mutation, however, fails to develop a tumor in human breasts, reducing the chances of a cancer.

They focused on the human epithelial tissues, the thin sheets of cells that line our vital organs. That’s because eighty percent of all human cancers begin in epithelial tissues. 

epithelial cells act as the body’s first barrier and are constantly exposed to stress, damage, and mutations. In fact, both the lung and the breast epithelial tissues display ‘epithelial defense against cancer’ — the epithelium’s natural act against tumorous cells. That’s why the group tested a specific cancerous mutation that occurs in both breast and lung epithelial tissues.

Researchers have long recognized that breast and lung epithelial tissues exhibit distinct differences. Breast epithelium is relatively stable and compact — the cells are tightly packed with stronger junctions. On the other hand, lung epithelium expands and relaxes with each breath, which is why its cells are more flexible, elongated, and loosely connected.

The group, through a combination of live imaging and computer models, has determined how these differences directly lead to the lung epithelium being more prone to growing tumors compared to the breast.

Once a cancerous mutation sets in the breast tissue, single mutant cells are pushed out, and groups of cells get stuck together. In lung tissue, the same mutant cells spread easily and make finger-like shapes.

The team found that the “tug-of-war” forces between normal and mutant cells decide whether cancerous cells are removed, trapped, or allowed to grow. Thus, cell mechanics help explain tissue-specific cancer risk. The surprise was how directly those mechanics determine whether mutant cells are restrained or allowed to spread.

A belt forms around the tumor in the breast epithelia, raises tension, jams the mutant cluster, and often forces out single mutants. Thus, this belt restrains the tumor.

In the lung epithelia, the cells are more elongated, motile, and weakly connected. So, no such belt forms, allowing the mutant cells to survive, grow longer, and spread into the tissue.

The group’s work demonstrates a pathway to resisting the growth of mutations into tumors, and eventually, into cancers. 

https://elifesciences.org/reviewed-preprints/106893v1

How much protein you really need

Most official guidelines recommend a bare minimum of close to one gram of protein per kilogram of body weight per day. But many scientists object to suggestions flying around social media that people need m.... Here’s what experts advise:

• Protein needs can vary from person to person and can change throughout a lifetime. “For older adults, 1.2 grams per kilogram is just giving them a little extra protection,” says nutrition and exercise researcher Nicholas Burd.
• Meeting your protein needs with plants rather than meat is better for your heart and the planet, but it might require a greater variety of foods (and maybe supplements).
• If you’re getting enough calories and eating a varied diet, you’re probably getting enough protein.
• For most people, unless you have kidney disease, too much protein won’t hurt you.

https://www.nature.com/articles/d41586-025-03632-1?utm_source=Live+...