Written by the Nuvirox Research Team
Key points
- Vitamins reliably reduce fatigue in one situation: when they correct a genuine deficiency. If your levels are already adequate, topping up tends to do little.
- If vitamins aren't helping, the likely reasons are that you weren't deficient, the cause is something a vitamin can't fix (sleep, stress, thyroid), or a real shortfall hasn't been confirmed by testing.
- Testing for specific gaps (iron/ferritin, B12, vitamin D, thyroid) is far more useful than guessing with a multivitamin.
Short answer: vitamins lift energy mainly when they're fixing a real shortage, so if you're not deficient, they often won't move the needle. It's one of the most consistent findings in the fatigue literature: correct a genuine deficiency and tiredness can improve markedly; supplement someone whose levels are already fine and the benefit largely disappears. So "tired even after taking vitamins" usually means one of three things, you weren't deficient, the vitamin isn't the right tool for your cause, or a real gap hasn't actually been identified. The fix is to find out what (if anything) you're short of, rather than stacking more pills.
Why don't vitamins always help with fatigue?
The mental model most people have, "vitamins give you energy", is slightly off. Vitamins are cofactors: they enable processes that turn food into usable energy, but only up to the point where you have enough. Beyond sufficiency, more doesn't mean more energy, because the bottleneck isn't the vitamin anymore. Picture a tank: if it's low, filling it helps a lot; if it's already full, adding more spills over without changing anything.
That's why the same B-vitamin or iron tablet can be transformative for one person and do nothing for another. The deciding factor isn't the supplement, it's whether there was a gap to close.
What does the evidence actually show?
When there's a deficiency, supplementing can clearly help. In a randomized controlled trial, non-anemic menstruating women with low ferritin and unexplained fatigue who took oral iron reported significantly less fatigue than those on placebo (Vaucher et al., 2012). An earlier randomized trial in similar low-ferritin women found fatigue dropped about 29% with iron versus 13% with placebo (Verdon et al., 2003). For the right person, the effect is real and meaningful.
When there's no real gap, the benefit largely vanishes, the honest counterweight. When researchers gave intravenous iron to non-anemic blood donors who had low ferritin but weren't notably fatigued, it raised their iron stores but produced no improvement in fatigue versus placebo (Keller et al., 2020). The pattern repeats across the energy-supplement literature: filling a deficiency helps; topping up an already-sufficient person does little. This is the single most important thing to understand about why your vitamins might not be working.
Study snapshot
Model: Non-anemic blood donors with low ferritin · Dose: Single 800 mg IV iron dose vs placebo · Duration: 6–8 week follow-up · Finding: iron stores rose but fatigue scores were no better than placebo (Keller et al., 2020)
If it's not a vitamin gap, what is it?
Often the cause of fatigue simply isn't something a vitamin addresses. The usual suspects, insufficient or poor-quality sleep, chronic stress, low physical activity, and conditions like thyroid disorders, sleep apnea, depression, or perimenopause, won't budge for a multivitamin because the bottleneck is elsewhere. If you've been diligently taking supplements and still feel wiped out, that's a strong hint the lever you need is somewhere other than the supplement aisle. Our overview of why you might be tired all the time walks through the broader list of causes, and if your fatigue is the run-down, low-reserve kind, our piece on feeling run down all the time goes deeper on rebuilding it.
What's worth testing before you supplement?
Because the benefit hinges on whether you're actually deficient, testing beats guessing. The fatigue-relevant labs worth discussing with a doctor include ferritin and a full blood count (iron status and anemia), vitamin B12 and folate, vitamin D, and thyroid function. Knowing your numbers turns supplementation from a shot in the dark into a targeted fix, and it spares you from taking things you don't need. It also flags causes a vitamin can't solve, so you don't keep chasing the wrong solution.
More is not safer. Some vitamins and minerals, including iron and the fat-soluble vitamins, can build up to harmful levels if over-supplemented. Confirming a deficiency before correcting it isn't just about effectiveness, it's about not taking high doses you don't need.
Where do NAD+ precursors fit in?
NAD+ precursors like nicotinamide riboside (NR) work on the cell's energy machinery and reliably raise blood NAD+ in human trials, roughly 60% at 1,000 mg/day in one crossover study (Martens et al., 2018), and dose-dependently in a larger one (Conze et al., 2019). But the same honesty applies: raising a biomarker isn't the same as guaranteed felt energy. A 2025 randomized trial in people with long-COVID found NR lifted NAD+ but did not significantly improve fatigue versus placebo (Wu et al., 2025). The sensible framing is that NAD+ support is one input among several, valued where the rationale fits, not a stimulant or a guaranteed fatigue cure.
Frequently asked questions
Why am I still tired even though I take a multivitamin every day?
Most likely because you weren't deficient in the first place, so there was no gap to fill, or because your fatigue stems from something a vitamin can't fix, like sleep debt, stress, or a thyroid issue. Testing for specific deficiencies is more informative than a blanket multivitamin.
Which vitamin deficiencies most commonly cause fatigue?
Iron (low ferritin, with or without anemia), vitamin B12, and vitamin D are common culprits, and thyroid problems often masquerade as a vitamin issue. A doctor can test these directly.
Could taking too many vitamins make me feel worse?
It can. Excess iron and fat-soluble vitamins (A, D, E, K) can accumulate to harmful levels. That's another reason to confirm a deficiency before supplementing rather than taking high doses on spec.
Should I try a stronger or more expensive supplement?
Not until you know whether you're deficient. If your levels are adequate, a pricier or higher-dose product is unlikely to help, the benefit comes from correcting a gap, not from the dose.
From Nuvirox
Why we formulated NAD+ Restore
We built NAD+ Restore around the precursor, with polyphenols in a supporting role — matching where the evidence is strongest. Each 2-capsule serving delivers 500 mg of Nicotinamide Riboside Chloride (NR), one of the two most-researched NAD+ precursors, within the dose range used in published human trials. Alongside it sit 150 mg trans-resveratrol (Japanese Knotweed) and 50 mg quercetin (Sophora japonica) — polyphenols studied alongside NAD+ pathways for cellular health support — plus 10 mg galactomannans from fenugreek to support absorption.
It comes with a 60-day money-back guarantee, long enough to actually evaluate it the way the research says you should.
Learn more about NAD+ Restore →The bottom line
If vitamins aren't touching your fatigue, the most likely explanation is that you weren't short of them, the evidence is clear that supplements help energy when they correct a real deficiency and do little otherwise. Rather than escalating to stronger pills, get the relevant levels tested (iron, B12, vitamin D, thyroid), and look hard at the causes a vitamin can't fix, like sleep and stress. Targeted beats blanket, and confirming a gap before filling it is both more effective and safer.
References
- Vaucher P, Druais PL, Waldvogel S, Favrat B. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ. 2012;184(11):1247-1254. DOI: 10.1503/cmaj.110950. PMID: 22777991.
- Verdon F, Burnand B, Stubi CL, et al. Iron supplementation for unexplained fatigue in non-anaemic women: double blind randomised placebo controlled trial. BMJ. 2003;326(7399):1124. DOI: 10.1136/bmj.326.7399.1124. PMID: 12763985.
- Keller P, von Kanel R, Hincapie CA, et al. The effects of intravenous iron supplementation on fatigue and general health in non-anemic blood donors with iron deficiency: a randomized placebo-controlled superiority trial. Sci Rep. 2020;10(1):14219. DOI: 10.1038/s41598-020-71048-0. PMID: 32848185.
- Martens CR, Denman BA, Mazzo MR, et al. Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults. Nat Commun. 2018;9(1):1286. DOI: 10.1038/s41467-018-03421-7. PMID: 29599478.
- Conze D, Brenner C, Kruger CL. Safety and metabolism of long-term administration of NIAGEN (nicotinamide riboside chloride) in a randomized, double-blind, placebo-controlled clinical trial of healthy overweight adults. Sci Rep. 2019;9(1):9772. DOI: 10.1038/s41598-019-46120-z. PMID: 31278280.
- Wu CY, Reynolds WC, Abril I, 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. PMID: 41357333.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for professional medical advice.