Vitamin B3 Linked to Younger Muscle Epigenetic Readings; Interval Training Mixed

The work is exploratory research in people. It draws on three separate studies that were not originally designed to be compared. One tested nicotinamide riboside (NR), a vitamin B3 form that the body uses to make NAD+, a molecule involved in energy use in cells. The other two tested high-intensity interval training (HIIT) on a stationary bike. The researchers call their analysis preliminary. It shows associations, not proof of cause.

The measure used was epigenetic age. Epigenetic clocks read chemical tags on DNA, called methylation, and turn the pattern into an estimate of biological age. The team applied seven clocks to muscle samples and looked at epigenetic age acceleration, meaning how far the reading runs ahead of or behind what is expected.

The NR data came from the Finnish Twin Cohort, in which adult twins aged 30 to 65 took NR for five months. The final dose was 1,000 mg a day. Muscle samples from the thigh (vastus lateralis) were available before and after for 30 people. Blood samples were available for 36 people. Some analyses compared leaner and heavier twins within pairs.

According to the study, NR was associated with reduced muscle epigenetic age acceleration. The effect was clearest on three clocks: PCHannum, MEAT and DunedinPACE. MEAT is the only clock built specifically for muscle. DunedinPACE estimates the pace of aging rather than an age in years.

The exercise data came from two studies. In EpiH, 20 younger and 20 older adults with overweight or obesity did six weeks of supervised HIIT, three sessions a week. In Gene SMART, healthy, moderately fit adults aged 18 to 48 did four weeks of HIIT, also three times a week. Gene SMART has enrolled 100 men and 30 women to date. The paper excerpt available to us does not give the final sample size for each clock analysis.

HIIT produced opposite effects in some clocks. Most notably, it increased the pace of aging as measured by DunedinPACE. The authors describe NR and HIIT as shifting muscle epigenetic aging in opposing directions, with responses that varied by person and by clock.

The researchers also checked mitochondria, the parts of cells that produce energy. Changes in muscle mitochondrial content tracked with changes in MEAT readings after NR and after six weeks of HIIT. The authors say this suggests a possible link between mitochondrial abundance and epigenetic clocks. It is a correlation, and the study does not show which drives which.

So what should a higher clock reading after hard training mean? On this evidence, not much yet. The readings were taken after only four to six weeks of training. The clocks were largely built for blood and to predict age, and the authors stress how much they differ across tissues and people. The available text does not report health outcomes such as strength, disease or lifespan in relation to these clock readings, so it cannot say that an older-looking clock reading after exercise is harmful. The authors note that earlier work linked HIIT to younger-looking methylation patterns, which adds to the uncertainty.

The same caution applies to NR. A lower muscle clock reading is not shown here to mean better muscle function or longer life. The authors note that earlier human NR results on whole-body outcomes have been mixed. The study also had no comparison arm described in the available text, and the groups were small.

The authors say further studies are needed to clarify how NR and exercise regulate epigenetic aging. Watch for larger, purpose-built trials that follow people for longer and pair clock readings with measures of muscle function and health.

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