Dietary Niacin Is Linked to Strength After 40—But Don’t Buy Pills Yet

NAD+ supplements get marketed as though muscle aging begins and ends with a capsule. The more relevant human finding may be less glamorous: higher niacin intake from food was associated with stronger grip, more favorable lean-mass measures, and lower insulin resistance in U.S. adults over 40. That result deserves attention. It does not prove that niacin caused any of those outcomes, and trials of supplemental NAD+ precursors have not established a comparable benefit in healthy adults.

The practical implication is modest but useful. Build meals around ordinary niacin-containing protein foods—poultry, fish, and legumes—because they also provide protein and other nutrients tied to muscle health. Do not treat the observational result as a reason to take high-dose niacin, nicotinamide, NMN, or NR.

What the NHANES study actually found

A 2024 analysis by Xiang et al. examined several overlapping NHANES datasets of U.S. adults older than 40. The grip-strength analysis included about 3,772 participants from 2011–2014. The glucose-homeostasis analysis included about 9,189 participants from 1999–2018. The body-composition analysis used DXA data from adults aged 40 to 60 across 2011–2018.

People who reported higher dietary niacin intake had greater grip strength, more favorable appendicular lean-mass indices, and lower HOMA-IR, a calculated marker of insulin resistance. The authors adjusted for 14 covariates, including age, sex, body mass index, physical activity, diabetes status, smoking, alcohol use, income, education, race and ethnicity, Healthy Eating Index-2015 score, and the percentage of calories from protein, fat, and carbohydrate.

Those adjustments make the analysis more informative than a simple comparison of people who eat different diets. They do not turn it into a trial. The study used dietary recall and measured exposure and outcomes within a cross-sectional design, so it cannot determine whether niacin intake improved muscle or glucose control.

The publication excerpts available here do not report a reproducible intake threshold, dose-response inflection point, confidence interval, or effect estimate for the associations. That limits any attempt to translate the findings into a target number of milligrams per day. The sensible conclusion is that higher reported intake tracked with better outcomes in these datasets—not that a particular extra dose will build muscle.

Why niacin is biologically plausible

Niacin includes nicotinic acid and nicotinamide, and the body can also make NAD+ from tryptophan. NAD+ participates in mitochondrial energy production, DNA repair, and metabolic signaling. Skeletal muscle has high energy demands, so a relationship between NAD+ precursor availability and muscle metabolism makes biological sense.

Biological plausibility is a starting point, not a verdict. Food intake can correlate with muscle health because of the food package rather than niacin itself. Poultry and fish, major niacin contributors in the NHANES analysis, also supply protein. A person eating more of those foods may have a different training routine, total energy intake, income, appetite, or overall diet than someone eating less.

The protein problem is not a footnote

Jun et al. analyzed NHANES data in 2022 and found that absolute dietary protein intake was independently associated with appendicular lean mass and handgrip strength among middle-aged U.S. adults. Those are the same broad outcomes that make the niacin finding appealing.

Xiang et al. adjusted for protein as a percentage of energy, which helps, but protein percentage is not the same as total grams per day. Two diets can devote the same share of calories to protein while delivering different absolute amounts. Because niacin-rich animal foods often deliver substantial protein, an unknown share of the niacin association may reflect protein intake or other characteristics of a protein-rich whole-food diet.

This does not make the niacin finding worthless. It tells us the finding needs a trial designed to separate niacin from protein and from the rest of the meal. Until then, food-first advice has an advantage: it does not require pretending the nutrient works alone.

A 2024 population-based study of older adults reached a compatible broader conclusion: multiple dietary nutrient variables were associated with appendicular lean mass, muscle function, and strength. Muscle maintenance rarely depends on one biochemical celebrity. Adequate calories, protein, activity, and a diet that supplies micronutrients all matter.

What supplement trials do—and do not—show

The best positive human supplement signal comes from a 2021 double-blind randomized trial by Yoshino et al. Fifty prediabetic postmenopausal women took NMN, 250 mg daily, or placebo for 10 weeks. NMN increased skeletal-muscle insulin sensitivity and improved measures of insulin signaling and muscle glucose disposal compared with placebo.

That is meaningful proof of concept for muscle glucose handling in that population. It was not a grip-strength or lean-mass trial. It also enrolled women with prediabetes and suppressed baseline insulin signaling, not metabolically healthy adults with adequate dietary niacin. The study therefore cannot establish that NMN improves muscle function in the general population, or that NMN recreates the association seen with food-source niacin.

The direct counterweight is a 2022 randomized trial by Connell et al. in physically compromised older adults. Participants received L-tryptophan, nicotinic acid, and nicotinamide—conventional NAD+ precursors—or placebo. The intervention did not improve mitochondrial function or skeletal-muscle function versus placebo.

The two trials differ in population, intervention, duration, and endpoints. Yoshino et al. tested NMN for 10 weeks and measured muscle insulin sensitivity in prediabetic postmenopausal women. Connell et al. tested a combination containing nicotinic acid and nicotinamide in physically compromised older adults and measured mitochondrial and muscle function. They cannot be averaged into a single answer. Together, they show that NAD+ precursor results depend heavily on who takes what and what outcome researchers measure.

A systematic review and meta-analysis of NMN trials in middle-aged and older adults is available, but the published summary available here does not provide extractable pooled effect values. It should not be used to manufacture certainty around NMN's effects on muscle or liver outcomes.

Why "more niacin" is the wrong message

The study supports a normal dietary pattern, not supplementation beyond nutritional adequacy. It does not show whether the apparent benefit plateaus at ordinary intake, whether it requires intake above standard recommendations, or whether added niacin changes any clinical outcome.

There is also an unresolved safety concern at elevated intakes. Research on the niacin metabolite 4-pyridone-3-carboxamide, or 4PY, has linked higher levels to cardiovascular inflammatory signals in a clinical study, but the available evidence here does not provide a verified source for that claim. That gap matters. Until the safety evidence and dose context are verified, no responsible reading of the NHANES data supports chasing higher niacin intake with supplements.

What to do with this evidence

If you are over 40 and want a diet that supports muscle and metabolic health, choose protein-rich whole foods such as poultry, fish, and legumes regularly, alongside resistance training and sufficient total protein. Those foods can raise dietary niacin intake while also delivering nutrients with a much firmer connection to muscle maintenance.

Food-source niacin is associated with better strength, lean-mass measures, and insulin-resistance markers in observational U.S. data. The evidence does not show that niacin pills, NMN, or any other NAD+ supplement will produce the same result in healthy adults.

The honest verdict is pleasantly unexciting: eat real food, train your muscles, and let randomized trials—not supplement labels—decide whether isolated NAD+ precursors earn a role.