Harvard 24-Week Trial: NR Boosts NAD⁺ Levels Threefold
Long COVID lingers like a persistent shadow, leaving hundreds of millions worldwide struggling with brain fog, fatigue, and insomnia.
In November 2025, a team from Harvard Medical School published a 24-week double-blind, placebo-controlled clinical trial in eClinicalMedicine, a journal in The Lancet family. The results showed that nicotinamide riboside (NR) increased NAD⁺ levels in the body by 2.6–3.1 times within five weeks. Exploratory analyses also suggested that after 10 weeks of continuous supplementation, participants experienced improvements in fatigue, sleep quality, depressive symptoms, and executive function.
SARS-CoV-2 infection activates PARP enzymes, which consume large amounts of NAD⁺.
Reduced NAD⁺ impairs mitochondrial function.
This contributes to uncontrolled inflammation and cognitive fatigue.
NR is currently one of the most clinically supported NAD⁺ precursors and has been shown to effectively raise NAD⁺ levels in blood and tissues.
Study design
High-dose intervention: 2000 mg of NR per day.
Long-term follow-up: 24 weeks, including both placebo and NR phases.
Key Finding 1: NR acts like a powerful “cellular charger”
The data were striking. After only 5 weeks of NR supplementation, participants’ blood NAD⁺ levels rose by 2.6–3.1 times. This demonstrates NR’s high bioavailability and its ability to rapidly replenish cellular energy capacity.
Key Finding 2: Positive signals in exploratory analyses
Although the strict statistical comparison between the NR group and the placebo group did not reach significance (the primary endpoint was negative), combining data from all participants during the NR phase (43 individuals) revealed several encouraging trends when compared with their own baseline before NR use.
Subjective cognitive reports (ECog) improved during both the placebo and NR periods. This suggests that perceived improvement may partly reflect expectation effects or natural symptom fluctuations over time.
Objective cognitive testing (TMT-B, measuring executive function) showed a different pattern: reaction speed improved significantly only during the NR supplementation phase.
Compared with subjective impressions, objective behavioral improvements are often considered stronger evidence of real physiological change. These findings therefore provide a noteworthy clue that NR may help alleviate long-COVID-related “brain fog.”
This trial offers reassuring evidence: even at 2000 mg per day, NR showed excellent tolerability.
Most adverse events were mild, mainly nausea or muscle cramps.
Only one serious adverse event occurred, and it was judged unrelated to NR.
Together, these can form a synergistic “energy metabolism + neuroprotection” formulation matrix.
500–1000 mg/day is a commonly used supplemental range.
Continuous use for at least 10–12 weeks is recommended before evaluating subjective effects.
High doses such as 2000 mg/day should be used under professional guidance.
This Lancet-affiliated study did not claim that “NR cures long COVID.” What it did show, through rigorous data, is that raising NAD⁺ levels and improving fatigue and sleep is a pathway worth exploring further.
Whether NR can become a true breakthrough for long COVID will require larger, more precise clinical trials.
For product developers seeking an NAD⁺ precursor backed by clinical evidence, NR remains one of the strongest current options in terms of both evidence and safety.
Reference：
Wu CY, et al. Effects of nicotinamide riboside on NAD+ levels, cognition, and symptom recovery in long-COVID: a randomized controlled trial. EClinicalMedicine. 2025;89:103633. doi: 10.1016/j.eclinm.2025.103633
In November 2025, a team from Harvard Medical School published a 24-week double-blind, placebo-controlled clinical trial in eClinicalMedicine, a journal in The Lancet family. The results showed that nicotinamide riboside (NR) increased NAD⁺ levels in the body by 2.6–3.1 times within five weeks. Exploratory analyses also suggested that after 10 weeks of continuous supplementation, participants experienced improvements in fatigue, sleep quality, depressive symptoms, and executive function.
PART 01
Why NR? — NAD⁺ as the “Master Switch” of Cellular Energy and Immunity
People with long COVID often exhibit NAD⁺ depletion:SARS-CoV-2 infection activates PARP enzymes, which consume large amounts of NAD⁺.
Reduced NAD⁺ impairs mitochondrial function.
This contributes to uncontrolled inflammation and cognitive fatigue.
NR is currently one of the most clinically supported NAD⁺ precursors and has been shown to effectively raise NAD⁺ levels in blood and tissues.
PART 02
The Trial: What Happened Over 24 Weeks?
This was a rigorously designed study involving 58 long-COVID patients suffering from brain fog.Study design
High-dose intervention: 2000 mg of NR per day.
Long-term follow-up: 24 weeks, including both placebo and NR phases.
Key Finding 1: NR acts like a powerful “cellular charger”
The data were striking. After only 5 weeks of NR supplementation, participants’ blood NAD⁺ levels rose by 2.6–3.1 times. This demonstrates NR’s high bioavailability and its ability to rapidly replenish cellular energy capacity.
Key Finding 2: Positive signals in exploratory analyses
Although the strict statistical comparison between the NR group and the placebo group did not reach significance (the primary endpoint was negative), combining data from all participants during the NR phase (43 individuals) revealed several encouraging trends when compared with their own baseline before NR use.
Subjective vs. Objective Cognitive Changes
An interesting nuance emerged:Subjective cognitive reports (ECog) improved during both the placebo and NR periods. This suggests that perceived improvement may partly reflect expectation effects or natural symptom fluctuations over time.
Objective cognitive testing (TMT-B, measuring executive function) showed a different pattern: reaction speed improved significantly only during the NR supplementation phase.
Compared with subjective impressions, objective behavioral improvements are often considered stronger evidence of real physiological change. These findings therefore provide a noteworthy clue that NR may help alleviate long-COVID-related “brain fog.”
NAD⁺ and Sleep Improvement
The study also found that the magnitude of NAD⁺ increase was significantly associated with improvements in sleep quality (p = 0.03), offering preliminary support for a possible “NAD⁺ mechanism → symptom improvement” pathway.
PART 03
Safety: Good Tolerability Even at High Doses
Many consumers worry about the safety of high-dose supplementation.This trial offers reassuring evidence: even at 2000 mg per day, NR showed excellent tolerability.
Most adverse events were mild, mainly nausea or muscle cramps.
Only one serious adverse event occurred, and it was judged unrelated to NR.
Conclusion
NR demonstrated a favorable safety and tolerability profile during long-term, high-dose use, supporting its potential application as a functional food or dietary supplement ingredient.Practical Implications for Product Developers and Consumers
Potential application areas
Post-COVID syndrome support.Chronic fatigue.Sleep disturbances.Suggested combination ingredients
NR may work synergistically with:PQQ (mitochondrial biogenesis).Coenzyme Q10 (electron transport chain support).NMN (another NAD⁺ precursor).Magnesium (nervous system calming support).Together, these can form a synergistic “energy metabolism + neuroprotection” formulation matrix.
Dosage and duration reference
Based on this study and previous literature:500–1000 mg/day is a commonly used supplemental range.
Continuous use for at least 10–12 weeks is recommended before evaluating subjective effects.
High doses such as 2000 mg/day should be used under professional guidance.
PART 04
Final Thoughts: A Small but Meaningful Step in Science
Scientific progress is rarely instantaneous, and science is never perfect — but each study helps refine the direction forward.This Lancet-affiliated study did not claim that “NR cures long COVID.” What it did show, through rigorous data, is that raising NAD⁺ levels and improving fatigue and sleep is a pathway worth exploring further.
Whether NR can become a true breakthrough for long COVID will require larger, more precise clinical trials.
For product developers seeking an NAD⁺ precursor backed by clinical evidence, NR remains one of the strongest current options in terms of both evidence and safety.
Reference：
Wu CY, et al. Effects of nicotinamide riboside on NAD+ levels, cognition, and symptom recovery in long-COVID: a randomized controlled trial. EClinicalMedicine. 2025;89:103633. doi: 10.1016/j.eclinm.2025.103633
