„Morning or evening?” and „With food or on an empty stomach?” are some of the most common practical questions regarding NAD+ precursors. However, studies specifically analysing the timing of intake are much more limited than those evaluating whether these compounds can influence biomarkers associated with NAD+.
In this article, we discuss what is currently known about NAD+ and circadian biology, the impact of meals, combining with resveratrol, and whether the importance of timing differs depending on the product form.
Morning or evening? What determines the right time?
There is a scientific basis for researching whether the time of day can affect NAD+ metabolism. However, this does not currently translate into a definitively established optimal time for taking NAD+ precursors.
Circadian rhythm rationale. Research published in 2009 by two independent teams demonstrated that NAD+ levels and the activity of NAMPT, an important enzyme in the NAD+ salvage pathway, oscillate over 24 hours in mice. These fluctuations were linked to the core circadian clock components CLOCK and BMAL1. NAD+ also interacts with circadian rhythm regulation via the NAD+-dependent enzyme SIRT1, creating a feedback loop between cellular NAD+ metabolism and the molecular circadian clock [1].
These results confirmed a significant mechanistic link between NAD+ metabolism and circadian rhythms in animal models. They also provide a scientific rationale for further research into whether the timing of NAD+ precursor intake can influence biological responses.
What human clinical data actually show. Evidence from humans is more limited. One study used magnetic resonance spectroscopy to measure brain NAD levels in 25 healthy participants during morning and afternoon sessions. The researchers found no significant effect of the time of day on NAD levels in the examined brain region. However, salivary cortisol measurements confirmed that the participants were assessed in different physiological states associated with circadian rhythms [2].
This means that while animal studies indicate circadian regulation of NAD+ metabolism at a mechanistic level, this human study found no significant difference between morning and afternoon in the studied brain NAD levels.
What this means in practice: current human clinical data does not confirm that taking a NAD+ precursor at one specific time of day produces significantly different effects than taking it at another time.
The involvement of NAD+ in circadian biology is well documented at the mechanistic level, particularly in animal studies, but this has not yet led to the establishment of a validated supplementation regimen in humans indicating the optimal time of day. In practice, taking the product regularly at a fixed time may be more justified than assuming that morning or evening is biologically better.
Should NAD+ be taken with food or on an empty stomach?
Research directly comparing the intake of NAD+ precursors with food and on an empty stomach is limited. No controlled human study has been identified that directly compares these conditions to determine differences in absorption or efficacy.
The main published human studies on nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) have generally not analysed the timing of intake relative to meals as an independent experimental variable. While some studies have used standardised instructions regarding supplement intake, including taking it in a specific relation to meals, these studies were not designed to determine whether taking it after a meal or on an empty stomach is better.
The overall tolerance of the supplement may also be significant. Taking an oral preparation with food can sometimes reduce gastrointestinal discomfort, but this does not automatically mean that food improves its absorption or biological activity. In some studies concerning NAD+ precursors, mild gastrointestinal symptoms have been reported.
Without direct comparative data, it cannot be stated that taking NAD+ precursors with food or on an empty stomach is consistently more effective. Individual tolerance and instructions concerning a specific formulation may therefore be more important than the assumption that one of these methods has been scientifically proven to be better.
Timing of administration when combined with resveratrol
NAD+ precursors and resveratrol are often discussed together, yet it is important to distinguish between mechanistic rationale and clinical evidence from human studies.
The mechanistic rationale for investigating such a combination is partly related to sirtuin biology. Resveratrol is a polyphenolic compound studied in the context of SIRT1, whilst enzymes from the sirtuin group require NAD+ for their enzymatic activity. This provides a biochemical rationale for investigating the interaction between compounds affecting NAD+ availability and substances associated with sirtuin pathways.
However, a mechanistic rationale does not mean that combining these substances provides additional clinical effects, nor that they must be taken at the same time.
What was actually studied in humans looks somewhat different. In one important published clinical trial, nicotinamide riboside was evaluated together with pterostilbene rather than resveratrol alone. Pterostilbene is chemically related to resveratrol, but has different pharmacokinetic properties. In this study, multiple administrations of the combination of NR and pterostilbene increased NAD+ levels over the study period. However, the timing of administration of the individual ingredients was not evaluated as an independent experimental variable [3].
This distinction matters because results concerning pterostilbene should not automatically be treated as direct evidence concerning resveratrol.
No dedicated published human clinical study has been identified that specifically evaluates the combination of an NAD+ precursor with resveratrol and compares whether taking these substances simultaneously or separately affects outcomes.
Therefore, there is currently a lack of sufficient direct clinical data to determine the „best time” to take an NAD+ precursor together with resveratrol. Recommendations to take them at the same time or at different times would therefore go beyond the available evidence regarding administration timing.
Does the administration time differ depending on the oral, sublingual, and injection forms?
The importance of timing may vary depending on the formulation and route of administration, although evidence to establish the optimal time remains limited.
Oral capsules and tablets: Current human clinical data do not indicate an optimal time of day for oral NAD+ precursors. Repeated-dose studies show that NAD+-associated biomarkers can change during regular exposure, but do not prove that a specific time of administration provides an advantage [4].
Sublingual forms: Adequate studies on humans regarding the optimal time for taking sublingual NAD+-related products have not been carried out. General rules for sublingual administration cannot be automatically transferred to NAD+ products without studies on the absorption of the specific formulation. Therefore, claims that a specific interval relative to meals or beverages significantly improves NAD+ absorption require direct evidence.
Injection (intramuscular/subcutaneous) and intravenous forms: the administration time depends on the specific formulation, research protocol or medically supervised use, rather than an established advantage of morning over evening. In published studies of intravenous NAD+, specific administration schedules were used, but it has not been shown that the time of day is an independent factor influencing efficacy [5].
Injection and intravenous administration also involve different issues regarding safety, sterility, pharmacokinetics and regulation compared to oral supplementation. Evidence concerning one route of administration should not be automatically extrapolated to another.
For all of these forms, available research does not indicate a single universal, optimal time for administering NAD+-related products. Where multiple administration was evaluated, adhering to a fixed study protocol has a much better scientific basis than claims regarding a specific time of day.
What happens if you take a product at the „wrong” time?
Current data does not indicate a specific period in the morning or evening as the „wrong” time to take a NAD+ precursor.
Available research on human brain NAD levels showed no significant time-of-day-dependent difference in the measured analysis [2]. Similarly, major studies on NAD+ precursors in humans have not typically indicated the time of administration as a controlled variable responsible for differences in primary outcomes.
This does not mean that the timing of administration has no biological significance. Research into circadian rhythms clearly indicates that NAD+ metabolism is linked to the molecular clock [1]. Rather, it means that current research on human supplementation has not yet established whether deliberately altering the time of administration produces clinically significant differences.
Regularity and adherence to the regimen are separate issues from circadian rhythm optimisation. In multiple-dose studies, NAD+-related biomarkers were assessed over several days or weeks, and the observed changes may diminish after supplementation ceases [4]. These results show that exposure over time matters for the biomarkers studied, but they should not be interpreted as evidence that sporadic differences in the time of administration are harmful or that an exact time every day is necessary.
Based on current evidence, there is insufficient justification for designating a single universal morning or evening window as the optimal time for administration. Therefore, specific times should not be presented as a proven method for increasing efficacy unless this is supported by human studies regarding the specific formulation.
Limitations of current evidence
- Basic research demonstrating the circadian regulation of NAD+ and NAMPT has been conducted mainly on mice. An available human study measuring brain NAD levels at different times of day showed no significant diurnal difference in the analysed parameter, which limits the possibility of directly translating the mechanism observed in animals into recommendations regarding the timing of supplementation in humans [1,2].
- No published human study has been identified that directly compares taking NAD+ precursors with food and on an empty stomach to determine which method is better.
- No published human study has been identified that specifically evaluates the combination of an NAD+ precursor with resveratrol and compares different times of administration. Evidence concerning the related compound, pterostilbene, should not be considered equivalent to evidence concerning resveratrol [3].
- Time of day, timing relative to meals, and timing relative to other supplements have generally not been analysed as controlled variables in major studies on NAD+ precursors. This significantly limits the possibility of formulating unambiguous evidence-based recommendations.
- Evidence regarding one NAD+ precursor, formulation, route of administration, dose or studied population cannot be automatically generalised to other products or groups.
Disclaimer
The article is for educational and scientific-information purposes only. It does not constitute medical advice, a diagnosis, therapeutic guidelines or a recommendation regarding the use of a supplement, injection or combination of different substances.
NAD+, NAD+ precursors, resveratrol and pterostilbene should not be presented as FDA- or EMA-approved treatments for diseases, unless referring to a specific approved medicinal product and indication. Changes in NAD+-related biomarkers do not in themselves constitute evidence of disease prevention, treatment, life extension, anti-ageing effects or other clinical benefits. A qualified healthcare professional should be consulted before using supplements or combining them with medicines, particularly during pregnancy or breastfeeding and in the case of medical conditions requiring treatment.
References
[1] Nakahata, Y., Sahar, S., Astarita, G., Kaluzova, M., & Sassone-Corsi, P. (2009). Circadian control of the NAD+ salvage pathway by CLOCK-SIRT1. Science, 324(5927), 654–657. https://doi.org/10.1126/science.1170803
[2] Cuenoud, B., Huang, Z., Hartweg, M., Widmaier, M., Lim, S., Wenz, D., & Xin, L. (2023). Effect of circadian rhythm on NAD and other metabolites in human brain. Frontiers in Physiology, 14, 1285776. https://doi.org/10.3389/fphys.2023.1285776
[3] Dellinger, R. W., Santos, S. R., Morris, M., Evans, M., Alminana, D., Guarente, L., & Marcotulli, E. (2017). Repeat dose NRPT (nicotinamide riboside and pterostilbene) increases NAD+ levels in humans safely and sustainably: A randomised, double-blind, placebo-controlled study. npj Aging and Mechanisms of Disease, 3, 17. https://doi.org/10.1038/s41514-017-0016-9
[4] Berven, H., Svensen, M., Eikeland, H., Tvedten, N., Sheard, E. V., Amdahl Af Geijerstam, S., Søgnen, M., McCann, A., Arnsten, L., Årseth, O., Skjeie, V., Hjellbrekke, A., Skeie, G.-O., Torres Cleuren, Y. N., Nido, G. S., Haugarvoll, K., Riemer, F., Tzoulis, C., & Dölle, C. (2026). The NAD-brain pharmacokinetic study of NAD augmentation in blood and brain using oral precursor supplementation. iScience, 29(3), 114764. https://doi.org/10.1016/j.isci.2026.114764
[5] Reyna, K., Heinzen, G., Patel, N., Ritter, M., Siojo, A., Legere, H., & Pojednic, R. (2026). Intravenous infusion of nicotinamide adenine dinucleotide (NAD+) versus nicotinamide riboside (NR): A retrospective tolerability pilot study in a real-world setting. Frontiers in Aging, 7, 1652582. https://doi.org/10.3389/fragi.2026.1652582