Safety of 3750 mg / day NR for 6 days
Relating my experiments with large doses of NR to the study on mice described in http://www.ergo-log.com/safe-dose-of-nicotinamide-riboside.html, and given my 70 kg mass and daily dose of 3750 mg, the comparable rat equivalent dose (RED) is given by
RED (mg/kg) = Human Dose (mg/kg) x [Human Km/Animal Km ]
= (3750/70) (37/3)
= 660 mg/kg
A RED dose of 660 mg/kg/day falls about halfway between the 300 and 1000 mg/kg published results. At the end of 90 days male rats in this range experienced about a 10% drop in weight (due to higher metabolism) and a slight increase in weight of the brain, kidney, liver and thymus. I judge these changes to be positive. At a higher dose of 1000 mg rats showed an increase in the concentration of white blood cells, which can be a sign of tissue damage.
From these results, it is likely that a dose of about 4000 mg per day for a week is safe in humans who weigh 70 kg. There may also be benefits to the brain, kidney, liver and thymus.
I think you may interpret the table wrongly. The relative organ weight is up but in absolute terms they shrink.
stefan_001, as you point out, the table of organ weights shows organ weight ratio relative to body weight at day 91. While relative organ weights are generally shown to increase, they decrease in absolute terms. At doses of up to 1000 mg/kg/day in rats, these absolute decreases were, in the words of the authors, “considered to be treatment related, but mild and potentially adaptive in nature due to prolonged exposure.”
Excerpts from the publication should help clarify interpretation of the results.
“Safety assessment of nicotinamide riboside, a form of vitamin B3” (2016) http://het.sagepub.c...tent/35/11/1149
Abstract
Nicotinamide riboside (NR) is a naturally occurring form of vitamin B3 present in trace amounts in some foods. Like niacin, it has been shown to be a precursor in the biosynthesis of nicotinamide adenine dinucleotide (NAD+). The safety of Niagen™, a synthetic form of NR, was determined using a bacterial reverse mutagenesis assay (Ames), an in vitro chromosome aberration assay, an in vivo micronucleus assay, and acute, 14-day and 90-day rat toxicology studies. NR was not genotoxic. There was no mortality at an oral dose of 5000 mg/kg. Based on the results of a 14-day study, a 90-day study was performed comparing NR at 300, 1000, and 3000 mg/kg/day to an equimolar dose of nicotinamide at 1260 mg/kg/day as a positive control. Results from the study show that NR had a similar toxicity profile to nicotinamide at the highest dose tested. Target organs of toxicity were liver, kidney, ovaries, and testes. The lowest observed adverse effect level for NR was 1000 mg/kg/day, and the no observed adverse effect level was 300 mg/kg/day.
Excerpts
At 1000 mg/kg/day of Niagen, increases in liver and kidney weights were statistically significant. All other relative to body weight organ weight changes, which reached statistical significance were likely secondary to decrease in terminal body weight and/or random biological variation and not considered treatment related.
Relative to brain weight, at 3000 mg/kg/day, there were statistically significant reductions in heart, epididymides, prostate and thyroid/parathyroid in males; liver, heart, ovaries and kidney were increased in females. In the nicotinamide-treated group, there were statistically significant reductions in weights of spleen, epididymides, testes and heart in males; liver weight was increased. At 1000 mg/kg/day there were no changes in organ weights relative to brain weight in males and a statistically significant increase in liver weight in females. No changes in organ weights relative to brain weights were seen in either males or females treated with 300 mg/kg/day of Niagen.
At 1000 mg/kg/day, there were statistically significant reductions in absolute organ weights of thyroid/parathyroid, pituitary and heart in males; no effects on absolute organ weights were seen in females. At 300 mg/kg/day, there were statistically significant reductions in absolute organ weights of brain and heart in males; no effects on absolute organ weights were seen in females.
Treatment-related histopathological changes were observed in liver, thyroid, kidneys, testes, epididymides, ovaries, and adrenals in both the 3000 mg/kg/day Niagen-treated and nicotinamide-treated groups.
NR administration at 1000 mg/kg/day dose level resulted in treatment-related organ weight changes in liver and kidney and increases in neutrophils, ALT and triglycerides, which were statistically significant in female rats only. Although these changes were considered adverse, based on their dose-dependent responsiveness, the increases in ALT and triglycerides occurred only in one gender and were below the twofold increase that is typically used as the cutoff for a biologically significant effect in the absence of histological results. The kidney weight increases at this dose also occurred in the absence of corresponding histopathology. Therefore, the liver and kidney effects at 1000 mg/kg/day were considered to be treatment related, but mild and potentially adaptive in nature due to prolonged exposure to this form of niacin. There were no treatment-related adverse effects noted at 300 mg/kg/day, although there was a slight decrease (8%) in overall body weight (day 90) at 300 mg/kg/day, which was considered adaptive. The NOAEL (no observed adverse effect level) and LOAEL (lowest observed adverse effect level) for NR were determined to 300 and 1000 mg/kg body weight/day, respectively.