Researchers develop a method for analyzing the content of NAD+ and its precursors in milk from different species and found NR, NMN, and NAD+ in human and donkey milk.(sergunt | iStock)
Vitamin B3 is a family of vitamins that includes three forms–nicotinamide (NAM), niacin (NA), and nicotinamide riboside (NR)–that are found naturally in some foods, added to foods, and sold as supplements. The vitamin B3 family participates in essential chemical reactions producing nicotinamide adenine dinucleotide (NAD+), a compound that helps enzymes do critical jobs for the body’s health. Interestingly, studies indicate that different related forms of vitamins (i.e., vitamers) for vitamin B3 at certain doses can boost intracellular NAD+ levels and may aid in treating metabolic and mitochondrial diseases.
For the first time, in a study published in Food Chemistry researchers quantified the amounts of vitamin B3 vitamers affecting NAD+ levels from different dairy species. To do so, the researchers tested the conversion of vitamin B3 vitamers to NAD+ based on a method that is fast, sensitive, affordable, and amenable to automation. This method is based on a fluorometric, enzyme-coupled assay–a way of determining the presence of a compound by measuring differences in fluorescence before and after a chemical reaction. “This analytical tool can be instrumental to select the most appropriate sources of the individual vitamers and to design better processing technologies to preserve their nutritional benefits,” said the investigators.
NAD+ is an essential molecule for many cellular processes and can be synthesized from a variety of compounds. NR, the most recently discovered form of vitamin B3, and nicotinamide mononucleotide (NMN) are potent supplements boosting NAD+ levels inside of cells. Indeed, through increasing NAD+ availability, NR and NMN administration enhance the activity of enzymes dependent on NAD+, which animal studies suggest result in protection against diet- and age-induced metabolic abnormalities.
The dietary precursors for the synthesis of intracellular NAD.
Vitamin B3 forms can be found as such in the diet or they can be formed from dietary NAD through a combined action of enzymes of the intestinal mucosa and the gut microbiota. Abbreviations: NA, nicotinic acid; NR, nicotinamide riboside; Nam, nicotinamide; NMN, nicotinamide mononucleotide; NAD, nicotinamide adenine dinucleotide (Ummarino 2016 | Food Chem.).
For these reasons, researchers developed a method based on a fluorometric, enzyme-coupled assay suitable for analyzing the content of NAD+ and its dietary precursors in milk from different species. The researchers showed that NR, NMN, and NAD+ were present in human and donkey milk, while they were selectively distributed in milk from cows, buffalo, sheep, and goats. Human milk was the richest source of NMN.
They saw that while most of the total vitamin B3 seems to be represented by NAD+ in sheep and goat milk, NR and NMN may account for a significant amount of the total vitamin B3 content in cow, buffalo, and human milk. “To our knowledge, this is the first evidence on the presence of NMN in a nutritional source, as well as the first quantitative determination of NR and NMN in food,” said the authors.
To assess NR bioavailability in processed foods, the researchers studied the influence of common heat treatments on cow milk content. The results showed that NR was resistant to pasteurization, but it was fully lost after the ultra-high temperature processing. “Our results indicate that NR does not resist [ultra-high temperature] treatment, therefore such process should be avoided in order to preserve the nutritional benefits of the vitamin,” said the authors.
Considering the nutritional importance of NR and NMN and the potential health benefits of their dietary supplementation through dairy products, a fast and sensitive assay targeting these nutrients would be of interest to the dairy industry. In particular, this method would enable the ability to assess the individual vitamer content in raw milk and monitor their stability during processing and storage.
According to the investigators, these findings might be of interest to small dairy enterprises to claim NR content in their products from minor dairy species, thus providing them with added value. The method might also be exploited to monitor NR levels in novel products intended to supplement the diet with a natural source of the vitamin; for example, probiotics selected for their ability to secrete NR.