Researchers from the University of California at Berkeley have thoroughly demonstrated that oxytocin, commonly known as the "love hormone," is strongly tied to muscle formation and regeneration. They suggest that oxytocin, which is most prominently linked to bonding behaviors, could be used to combat, or even prevent, the deterioration of muscle mass, strength, and agility as we age.

It's a sad fact of life that as we grow older our muscles atrophy, or decrease in size. Starting around age thirty, the average person loses about 1% of their muscle mass every year. The process accelerates in our later years, so that by the time we're closer to the century mark than the 50-year halfway line, we're probably hobbling and hunched -- hopefully not too hunched.

Regular weightlifting and exercise check the decline, but still, even the bulkiest 60-year-olds cannot match the strength or power of less-trained thirty-year-olds.

For a look at the cause of age-related muscle atrophy, sneak a peak at the bicep muscle on one of your arms -- feel free to flex it, if you want. Inside the muscle tissue are long, tubular cells called myocytes that work in unison to contract and move. Scattered amongst the myocytes are relatively dormant muscle stem cells, which stir to action when the hard-working myocytes become damaged. When awakened, they repair existing muscle tissue or grow into myocytes and build new muscle. However, as we age, the stem cells don't activate as promptly or efficiently as when we're younger. Scientists aren't exactly sure why, but one thing they have discovered is that sewing a young mouse and an old mouse together, a process called parabiosis, causes the muscles of the older mouse to regenerate almost like they're young again.

That procedure is tad macabre, however, and isn't exactly workable with humans. The new finding about oxytocin, published today in Nature Communications, is vastly more promising.

The Berkeley team, led by Christian Elabd and Wendy Cousin, first noted that aged mice (18 to 24 months) have about three times less oxytocin than their younger (2 to 4 months) counterparts. They subsequently performed an experiment, first administering oxytocin to one group of old mice and a placebo to another, then giving oxytocin, an oxytocin inhibiter, or a placebo to three different groups of young mice. All the mice were subsequently injected them with a toxin that damages muscle. In the wake of the injury, old mice that were given oxytocin formed a similar number of new muscle fibers as much younger mice that were given only a placebo. They also formed significantly more muscle fibers than old mice given a placebo. Moreover, young mice that were made to produce less oxytocin regenerated muscle almost like they were elderly. Oxytocin didn't boost the regenerative capabilities of young mice.

In a second experiment, the researchers bred mice that were deficient in oxytocin and watched how they grew in comparison to their normal littermates. After 12 months, the mice that produced less oxytocin had 32% and 22% less muscle mass in the two muscles analyzed in the leg: the gastrocnemius and the anterior tibialis.

The results of the two experiments provide clear evidence that oxytocin is tied to muscle regeneration. The next step is to test oxytocin out in human trials. Considering that the hormone is already widely used in medicine (PDF), easily administered via the nose, and has minimal side effects, we should know fairly soon whether or not the results carry over to people.

Source: Elabd, C. et al. Oxytocin is an age-specific circulating hormone that is necessary for muscle maintenance and regeneration. Nat. Commun. 5:4082 doi: 10.1038/ncomms5082 (2014).