Microbial species in the genus Lactobacillus, found in the human intestine as well as in fermented foods like yogurt and kefir, are known to provide health benefits to us. A number of important health benefits have been associated with increased populations of intestinal Lactobacillus, such as protection from fungal/Candidal overgrowth and vaginitis, reduction of the dysbiosis of irritable bowel syndrome/small intestinal bacterial overgrowth, and reduced unhealthy oral bacteria (e.g., Streptococcus mutans) that cause cavities.

Of the nearly 200 known species of Lactobacillus, however, one species is beginning to stand out: L. reuteri. There are about a dozen studies that demonstrate that L. reuteri probiotic supplementation (typically around one billion CFU doses) reduces intestinal inflammation, reduces constipation, and reduces the severity and duration of diarrheal diseases and unexplained abdominal pain in children. But a new collection of observations in experimental models coming from MIT and the University of Thessaloniki in Greece suggest that L. reuteri strain in particularly may also yield some dramatic age-reversing effects. While supplementing experimental mice with this microbial species, the investigators noted that the mice began to appear younger in as little as one week. They therefore pursued this line of research and documented that L. reuteri supplementation:

  • Increased blood testosterone levels in males dramatically (by up to 800% over the negligible levels seen in aged mice), as well as increasing testicular size and Leydig cell volume. (Leydig cells produce testosterone.) A reduction of Leydig cells and testicular size, along with a reduction in testosterone, are among the changes that occur in aging human males, effects associated with reduced libido, sexual interest/performance, increased visceral fat accumulation/weight gain, decreased muscle and bone density, and cognitive impairment.
  • Caused thicker, more luxuriant fur to develop in aged mice that was associated with increased sebum production, increased number of sebocytes that produce sebum, and (markedly) increased dermal thickness. Thicker hair and smoother skin, of course, are hallmarks of youth. Incredibly, these changes began as early as one week after probiotic supplementation, likely due to the increased sebum and sebocyte density.
  • Was associated with anti-inflammatory effects (increased levels of anti-inflammatory interleukin-10 and decreased interleukin-17) that may account for the increase in testicular volume (since hypogonadism or testicular atrophy can result, in part, from inflammation) and normalizes intestinal immune responses.
  • Was associated with marked acceleration of wound healing. (Note how quickly children recover from an injury compared to older adults.)
  • Was associated with slenderness, in comparison to overweight/obese unsupplemented mice.
  • Was associated with greater physical activity and increased muscle mass.

(Notably, the L. reuteri strain ATCC PTA 6475 was used.)

Whether parallel hormonal changes develop in females is not yet clear.

These are unprecedented observations with magnitudes of changes that are staggering. The tantalizing question is, of course, whether humans will likewise experience smoother, thicker skin with thicker, more luxuriant hair, and whether human males will experience increased testosterone levels via increased testicular Leydig cell volume? And, if such age-reversing effects develop via some metabolite produced by L. reuteri, what other potentially age-reversing effects might develop?

We need to bear in mind that these observations were generated in mice, not humans, though most microbiome observations that have made in mice have held true in humans, also.

Next: My high-dose personal L. reuteri experiment.