A Few Key Scientific Findings Regarding Human Muscle Growth and Maintenance after Young Adulthood
As well as the initial results of a personal test of these findings -- brief and to the point
The General Problem
When people are young and actively growing, there is a direct positive linear relationship between how much amino acid-containing protein they eat and how much muscle they subsequently build and maintain (Layman 2024); i.e., the more protein they consume every day, the more muscle tissue they build and maintain. In addition to the biochemical efficiency of this process in the young, muscle repair and growth continues in their bodies uninterrupted after each meal as long as amino acids from that most recent meal are still present in their blood.
On the other hand, as humans move on into their middle years and beyond, this positive linear relationship between the amount of protein eaten in a meal and the amount of muscle added and repaired weakens. For a start, in older people it takes higher levels of mealtime protein consumption just to initiate the muscle repair and building process. If insufficient protein is taken in at one time, little or no muscle building or re-building takes place – or can take place.
Besides this general cellular reluctance to start up the muscle building and repair process if too little protein is eaten in a meal, once begun the muscle building and repair process in older people only lasts for a couple of hours after the meal – even if abundant amounts of amino acids are still present in the blood.
When this multi-causal muscle cell growth and replacement problem is not addressed consciously and consistently, it inexorably leads to the muscle loss (sarcopenia) that eventually causes aging people to become physically incapacitated. The same problem also leads at the same time to gradually increasing vital organ dysfunction (ibid.) as amino acids needed to repair those organs at night and during other periods of catabolism grow in ever shorter supply.
As Layman (2024) explains, the foreshortened pulse of muscle growth and repair that takes place after older people eat a sufficiently proteinaceous meal evidently occurs because of exhaustion of cell-level (mitochondrial) energy reserves after the protein synthesis cellular work has begun. This apparently underlying biological problem that significantly limits muscle repair and growth in aging humans is reflected in the graphs below showing the marked decline of energy-generating cellular NAD+ stores (and causally-related ATP stores) that begins to develop immediately after young human adulthood.
Working Around the Age-Blunted Muscle Synthesis Problem
However, Pirinen et al., 2020, demonstrated that a once-a-day evening dose of NAD+-boosting time-release niacin of 750 to 1000 mg/day markedly increased the muscle mass and decreased the fat mass of healthy human control subjects (n=10, average age 50 years, range 25-64 years: 8 females, 2 males) after 4 months. See graphs below.
Note that my wife and I (both in our early 70s) recently tested the Pirinen et al., 2020, study results by augmenting our normal diet with twice daily oral niacin supplementation with, respectively, 1/32 teaspoon and 1/16 teaspoon inositol hexanicotinate with the semiquantitative consequences depicted below. The half-life of inositol hexanicotinate is approximately 10 hours, so its twice daily supplementation is believed to have kept our cellular and blood NAD+ levels more elevated than was previously normal throughout each day and night following the start of supplementation. Again, the results of our test of the Pirinen group’s niacin supplementation study are provided in the graphs below.
Inositol hexanicotinate supplementation took place throughout the shaded date areas shown in each of the graphs. The evident significant increases in muscle mass, decreases in fat mass, and increases in bone mass, all occurred more or less immediately after the start of daily niacin supplementation and have held more or less constant since. The changes in muscle and fat mass shown are entirely consistent with the results of the Pirinen study. While Pirinen et al. did not test changes in the bone mass of their subjects, given the ordinary loss of bone mass with age, our bone mass increases following this very minor nutritional augmentation are quite encouraging.
All semi-quantitative measurements of muscle, fat, and bone mass were made with a Withings Body Cardio scale.
