Evidence reviews on vitamins, minerals, and supplement efficacy.
96 claims reviewed
Moderate evidence suggests 5-HTP may improve depressive symptoms by increasing serotonin synthesis, with some RCTs showing efficacy comparable to SSRIs. However, most studies are older, small, and methodologically limited, and safety concerns exist regarding long-term use.
Moderate evidence suggests ashwagandha may modestly increase testosterone levels in men, particularly those under physical or psychological stress. Effect sizes are typically 10-22% above baseline, but clinical significance for healthy young men remains uncertain.
Moderate evidence suggests berberine positively modulates gut microbiome composition, increasing beneficial short-chain fatty acid producers and reducing pro-inflammatory taxa. However, most data comes from metabolic disease populations, and effects in healthy individuals are less clear.
Moderate evidence from meta-analyses supports berberine supplementation reducing fasting blood glucose and HbA1c in individuals with type 2 diabetes. Effects are comparable to metformin in some trials, though one study found minimal benefit over placebo in non-diabetic populations.
Moderate evidence suggests oral astaxanthin supplementation may reduce UV-induced skin damage markers including erythema, DNA damage, and moisture loss. Effects are modest and do not replace sunscreen, but may provide an adjunctive photoprotective layer.
Moderate evidence suggests berberine lowers blood sugar through partially overlapping mechanisms with metformin, with comparable HbA1c reductions in some trials. However, it is not a validated pharmaceutical replacement and lacks the safety and regulatory oversight of metformin.
Moderate evidence supports beta-alanine for improving exercise capacity in efforts lasting 1-10 minutes by increasing intramuscular carnosine, which buffers hydrogen ions. Performance benefits average 2-3% for high-intensity endurance but are minimal for longer steady-state efforts or short sprints.
Moderate evidence suggests black seed oil (Nigella sativa) has anti-inflammatory properties, primarily through its active compound thymoquinone. Clinical trials show reductions in CRP and other inflammatory markers, though effect sizes vary and study quality is inconsistent.
Weak evidence suggests boron supplementation may modestly increase free testosterone, primarily by reducing sex hormone-binding globulin (SHBG). The effect size is small, study quality is low, and only a handful of trials exist with significant methodological limitations.
Moderate but early evidence suggests CBD has anxiolytic properties, particularly for acute situational anxiety. A handful of well-designed RCTs show benefit at doses of 300-600mg, but evidence for chronic generalized anxiety remains limited and product quality varies enormously.
Moderate evidence supports citrulline's ability to improve blood flow via nitric oxide production. L-citrulline converts to L-arginine in the kidneys, which then produces nitric oxide to promote vasodilation. Effects are most notable in clinical populations with existing vascular impairment.
Moderate evidence suggests hydrolyzed collagen peptides improve skin hydration, elasticity, and reduce wrinkle depth after 8-12 weeks of supplementation. Effects are modest but measurable.
Weak evidence exists for copper peptides (GHK-Cu) promoting hair regrowth. In vitro studies show stimulation of hair follicle cells and promotion of angiogenesis, but only one small human study exists for hair loss. Most evidence is extrapolated from wound healing research rather than direct hair loss trials.
Moderate evidence supports that hydrolyzed collagen supplementation (10-15g/day) reduces joint pain in osteoarthritis patients and activity-related joint pain in athletes. Effects are modest and typically require 3-6 months of consistent use.
Weak evidence supports bovine colostrum supplementation boosting immunity. While colostrum contains immunoglobulins and growth factors, human studies show inconsistent immune benefits. Some trials report reduced upper respiratory infections in athletes, but immunological biomarker changes are generally not statistically significant.
Moderate evidence supports CoQ10 supplementation for heart failure patients, with the Q-SYMBIO trial showing reduced cardiovascular mortality. Evidence for prevention in healthy individuals is weaker, and benefits for statin-related muscle pain are inconsistent.
Moderate evidence suggests creatine supplementation may benefit cognitive function in older adults, particularly under conditions of mental fatigue, sleep deprivation, or stress. Brain creatine levels decline with aging, and supplementation may partially restore cerebral energy metabolism, though large definitive RCTs are still needed.
A single 2009 study found creatine raised DHT levels in rugby players, but no study has directly measured hair loss from creatine use. The fear is largely unsupported by current evidence.
Strong evidence indicates that creatine supplementation is safe for kidneys in healthy individuals. Multiple long-term studies and meta-analyses show no adverse effects on renal function markers despite transient increases in creatinine levels, which are an expected byproduct of creatine metabolism rather than a sign of kidney damage.
Strong evidence from extensive meta-analyses confirms creatine monohydrate supplementation improves high-intensity, short-duration exercise performance by 5-15%. It is one of the most well-researched and effective ergogenic aids available, with benefits for strength, power, and repeated sprint ability.
Moderate evidence suggests creatine may improve short-term memory and reasoning ability, particularly under conditions of sleep deprivation or cognitive stress. Effects in well-rested, healthy adults are smaller and less consistent.
Weak evidence suggests creatine may have modest effects on bone mineral density when combined with resistance training, but standalone supplementation shows minimal benefit. Most positive findings are in postmenopausal women and remain preliminary.
Weak evidence suggests creatine may increase DHT levels. This claim stems primarily from a single RCT in rugby players showing a 56% DHT increase after loading. No replication studies have confirmed this finding, and the mechanism remains unclear.
Moderate evidence indicates that a creatine loading phase (20g/day for 5-7 days) saturates muscle stores faster but is not necessary. Low-dose daily supplementation (3-5g/day) achieves the same saturation within 3-4 weeks. Loading is optional for faster results but offers no long-term advantage.
Weak evidence suggests curcumin may have neuroprotective properties, but extremely poor bioavailability limits its practical cognitive benefits. Most positive findings come from bioavailability-enhanced formulations in small trials with short follow-up.
Moderate evidence from meta-analyses suggests curcumin supplementation can reduce inflammatory markers (CRP, IL-6, TNF-alpha), particularly in populations with elevated baseline inflammation. However, curcumin has extremely poor bioavailability, and concerns about its chemical properties as a promiscuous assay interferer complicate interpretation.
Moderate-to-low evidence suggests curcumin may reduce depression symptoms, with several meta-analyses showing statistically significant effects. However, methodological limitations, small sample sizes, and low bioavailability raise questions about clinical utility.
Moderate evidence suggests elderberry supplementation may reduce the duration and severity of upper respiratory infections, particularly colds, by 1-2 days. Evidence for prevention is weaker. Most positive trials are small, and a large 2021 RCT showed no significant benefit.
Moderate evidence suggests elderberry supplementation may reduce the duration and severity of upper respiratory infections by 1-2 days. A meta-analysis supports modest efficacy, but the evidence base consists of small trials with methodological limitations and potential industry funding bias.
Weak evidence suggests fenugreek may modestly influence testosterone-related outcomes, but most studies show improvements in subjective libido rather than significant changes in serum total testosterone. Methodological concerns limit confidence.
Strong evidence from systematic reviews and clinical practice guidelines confirms that omega-3 fatty acid supplementation (EPA and DHA) significantly reduces triglyceride levels in a dose-dependent manner, typically by 15-30%. However, this triglyceride reduction does not consistently translate to reduced cardiovascular events.
Strong evidence from multiple meta-analyses confirms that garlic supplementation produces clinically meaningful reductions in blood pressure, particularly in hypertensive individuals. Aged garlic extract appears most effective, with average reductions of 8-10 mmHg systolic in those with elevated baseline pressures.
Evidence on glucosamine for joint pain is genuinely conflicting. Industry-funded trials and earlier meta-analyses show moderate benefit, while large independent RCTs and Cochrane reviews find effects are clinically insignificant. The discrepancy appears driven by trial quality and funding source.
Weak evidence that glutamine supplementation improves muscle recovery in healthy, well-fed athletes. While glutamine is critical for immune function and gut health, plasma levels rarely drop low enough in recreationally active people to warrant supplementation. Most RCTs show no benefit for soreness, strength recovery, or muscle protein synthesis when protein intake is adequate.
Evidence for glucosamine slowing structural joint degeneration is weak and conflicting. While some earlier trials suggested modest structure-modifying effects, a landmark 2010 BMJ network meta-analysis found glucosamine clinically ineffective for osteoarthritis.
Weak evidence supports high-dose vitamin C as a cancer treatment. Intravenous (IV) vitamin C shows some anticancer activity in preclinical models and early-phase trials, but large RCTs of oral vitamin C found no survival benefit. IV vitamin C may improve quality of life in advanced cancer but is not a proven anti-tumor therapy.
Moderate evidence from multiple RCTs suggests oral hyaluronic acid (HA) may reduce knee joint pain and improve function in osteoarthritis patients. Effects are modest but consistent across studies, with high-molecular-weight HA showing slightly better outcomes.
Moderate evidence supports L-theanine for reducing situational anxiety and promoting relaxation without sedation. Multiple RCTs show increased alpha brain wave activity and reduced stress markers, though long-term clinical anxiety disorder evidence is limited.
Weak evidence suggests lion's mane mushroom may reduce anxiety symptoms. While preclinical studies show promising anxiolytic effects, human clinical trials are scarce, small in sample size, and methodologically limited, preventing firm conclusions.
Weak evidence suggests lion's mane (Hericium erinaceus) promotes nerve growth factor (NGF) synthesis in vitro and accelerates peripheral nerve regeneration in animal models. Human evidence for nerve damage repair is extremely limited and confined to small preliminary trials.
Moderate evidence from several small RCTs suggests maca root may improve subjective sexual desire in both men and women, without altering sex hormone levels. Effects appear independent of hormonal changes, and the mechanism remains unclear.
Observational studies and meta-analyses consistently associate low vitamin D levels with worse COVID-19 outcomes, but RCTs of vitamin D supplementation in hospitalized patients have shown mixed results, leaving the causal relationship uncertain.
Moderate evidence that magnesium supplementation reduces anxiety symptoms, particularly in people with low magnesium status or high stress. The glycinate form may have additional calming effects from the glycine component. However, most studies use various magnesium forms rather than glycinate specifically, and placebo-controlled evidence for glycinate alone is limited.
Strong evidence supports magnesium citrate improving bowel regularity. Its osmotic mechanism is well-established, and clinical trials demonstrate increased stool frequency and improved consistency in both constipated patients and healthy adults with suboptimal bowel habits.
Moderate evidence supports magnesium supplementation (400-600mg/day) for migraine prevention, with frequency reductions of approximately 40% observed primarily in individuals with documented magnesium deficiency.
Moderate evidence supports magnesium supplementation for migraine prevention, with meta-analyses showing reduced frequency and intensity of attacks. However, study quality is heterogeneous, optimal formulations are unclear, and the evidence base has significant methodological limitations.
Moderate evidence suggests magnesium supplementation may improve sleep quality, particularly in older adults and those with low magnesium intake. Effects include reduced time to fall asleep and improved subjective sleep quality.
Weak evidence suggests magnesium may support testosterone levels primarily in deficient individuals or those under heavy physical stress. In magnesium-replete healthy adults, supplementation shows minimal testosterone-boosting effects.
Meta-analyses show magnesium supplementation produces modest blood pressure reductions of 2-4 mmHg systolic. Benefits appear limited to individuals who are magnesium-deficient, with minimal effects in replete individuals.
Weak evidence supports magnesium supplementation for muscle cramp reduction. Despite biological plausibility, most well-designed RCTs find no significant benefit over placebo for exercise-associated or nocturnal leg cramps in the general population.
Preliminary evidence from a small number of trials suggests magnesium supplementation may improve mild-to-moderate depression symptoms, particularly in those with low magnesium intake. However, the evidence base is small, and observational study limitations complicate interpretation.
Moderate evidence suggests magnesium L-threonate (MgT) can elevate brain magnesium levels more effectively than other forms. Animal studies consistently show increased cerebrospinal fluid magnesium, though human data confirming direct BBB transport remains limited.
Weak evidence—large meta-analyses and RCTs consistently fail to demonstrate that daily multivitamin use reduces all-cause mortality in well-nourished populations. Any benefits appear limited to specific deficient subgroups rather than the general population.
Weak evidence for performance benefits. While NAD+ precursors (NR, NMN) successfully raise blood NAD+ levels, human trials have largely failed to demonstrate meaningful improvements in exercise performance, VO2max, or endurance in healthy adults.
Moderate evidence supports NAC for liver health, particularly in acetaminophen toxicity where it is the standard of care. For broader hepatoprotection, evidence is promising but less definitive, with benefits seen in non-alcoholic fatty liver disease and alcohol-related liver injury in smaller trials.
Moderate but conflicting evidence exists for omega-3 supplementation improving dry eye symptoms. Earlier studies and meta-analyses favored benefit, but the large DREAM trial found no advantage over placebo, creating uncertainty about true efficacy.
Strong evidence shows omega-3 fatty acids (EPA and DHA) reduce inflammatory markers, particularly C-reactive protein and IL-6. Effects are most pronounced in people with elevated baseline inflammation.
Moderate evidence from meta-analyses of RCTs suggests EPA-predominant omega-3 supplementation produces a small-to-moderate antidepressant effect (SMD ~0.28), particularly as adjunctive therapy. Pure DHA shows minimal benefit. Effects are most consistent in clinical depression rather than subclinical low mood.
Strong evidence confirms that omega-3 fatty acid supplementation (EPA and DHA) reduces triglyceride levels by 20-30% at prescription doses, with dose-dependent effects. This is one of the most well-established supplement effects. However, triglyceride reduction does not consistently translate to reduced cardiovascular events.
Moderate evidence confirms oregano oil demonstrates antibacterial activity in vitro against many common pathogens, primarily through its carvacrol and thymol content. However, translation to clinical efficacy in humans is poorly supported, and in vivo evidence for treating bacterial infections is limited.
Moderate evidence suggests phosphatidylserine (PS) can blunt cortisol responses to physical and psychological stress. Effects are most consistent at doses of 600-800mg daily, though lower doses show weaker results. The magnitude of cortisol reduction is modest (15-30%) and primarily observed during acute stress challenges.
Moderate evidence supports specific probiotic strains for specific conditions (antibiotic-associated diarrhea, IBS), but most commercial products lack evidence for their particular strain combinations and general 'gut health' claims remain poorly defined.
Multiple meta-analyses suggest probiotics reduce C. difficile infection risk by 50-60% when co-administered with antibiotics. However, the largest pragmatic trial (PLACIDE) found no benefit in elderly hospitalized patients, raising questions about generalizability.
Moderate evidence from meta-analyses supports that certain probiotic strains improve global IBS symptoms, abdominal pain, and bloating compared to placebo. However, the field is hampered by inconsistent strain selection, high heterogeneity, and difficulty determining which specific probiotics benefit which IBS subtypes.
Strong evidence supports probiotics reducing the incidence of antibiotic-associated diarrhea. Multiple Cochrane reviews demonstrate a relative risk reduction of 37-42% when probiotics are co-administered with antibiotics, with Lactobacillus and Saccharomyces boulardii showing the most consistent evidence.
Moderate but limited evidence suggests quercetin has antihistamine and mast cell-stabilizing properties that may reduce allergy symptoms. In vitro studies are compelling, but human clinical trials are few, small, and show modest effects compared to conventional antihistamines.
Moderate evidence supports rhodiola rosea's ability to reduce mental and physical fatigue. Multiple RCTs show improvements in fatigue scores during stress and prolonged cognitive work, though effect sizes are modest and study quality varies.
Moderate evidence supports selenium's role in protecting thyroid function, particularly in reducing thyroid peroxidase antibodies in autoimmune thyroiditis. The thyroid contains the highest selenium concentration per gram of any organ, and supplementation appears most beneficial in selenium-deficient populations.
Weak evidence from two small clinical trials suggests shilajit may modestly increase testosterone levels in healthy men. Studies are limited by small sample sizes, short durations, and manufacturer funding. The magnitude of testosterone increase may not be clinically meaningful.
Moderate evidence suggests spirulina may enhance certain immune markers, particularly natural killer cell activity and cytokine production. However, most studies are small and short-term, limiting confidence in clinical relevance.
Very strong evidence from large meta-analyses of randomized trials demonstrates that statins reduce major cardiovascular events by approximately 20-25% per 1 mmol/L reduction in LDL cholesterol, with consistent benefits across diverse populations.
Moderate evidence shows testosterone replacement in older men with low levels modestly improves sexual function, mood, and bone density, but cardiovascular safety remains uncertain and benefits are smaller than commonly claimed.
Moderate evidence that tongkat ali (Eurycoma longifolia) modestly increases testosterone in men with low or borderline-low levels, particularly in stressed or aging populations. Effects in young healthy men with normal testosterone are less clear. Quality and standardization of extracts vary significantly.
Weak evidence suggests tongkat ali (Eurycoma longifolia) may reduce cortisol levels by 10-16% in moderately stressed adults. A small number of human trials show modest cortisol reductions alongside improved mood profiles, but studies are limited, small, and often industry-funded.
Weak evidence supports trace mineral supplementation for energy improvement in the general population. Benefits are primarily observed in deficient individuals. For those with adequate dietary intake, supplementation shows no meaningful energy enhancement in controlled trials.
Moderate evidence shows curcumin (the active compound in turmeric) reduces pain and inflammation in osteoarthritis, comparable to NSAIDs. Benefits for other pain conditions are less clear, and bioavailability remains a challenge.
Moderate evidence supports L-tyrosine improving cognitive performance specifically under stressful conditions (sleep deprivation, cold exposure, multitasking demands) where catecholamine depletion occurs. Benefits are minimal or absent under normal, non-stressed conditions.
Strong evidence supports topical vitamin A derivatives (retinoids) for improving photoaged skin. Prescription tretinoin is the gold standard with 40+ years of clinical data showing increased collagen, reduced wrinkles, and improved texture. Over-the-counter retinol is less potent but still effective.
Weak evidence that B12 supplementation boosts energy in people with adequate B12 levels. Fatigue improvement occurs only in those with genuine B12 deficiency. For the majority of people with normal B12 status, supplementation does not increase energy, alertness, or reduce fatigue.
Weak evidence suggests high-dose vitamin B6 before bed may modestly increase dream recall and vividness. Only one rigorous RCT exists showing a small but significant effect, while earlier pilot data is methodologically limited. The mechanism is plausible but unconfirmed.
Moderate evidence indicates vitamin C does not prevent colds in the general population but may reduce cold duration by 8-14% when taken regularly. Benefits are more pronounced in people under heavy physical stress.
Weak evidence links vitamin D supplementation to athletic performance improvements. Correcting deficiency may restore baseline function, but supplementation above adequate levels does not enhance performance in vitamin D-sufficient athletes.
Regular vitamin C supplementation modestly reduces cold duration by about 8% in adults and 14% in children, but taking it after symptoms start shows no consistent benefit. The effect is more pronounced in people under physical stress.
Moderate-to-good evidence supports vitamin D's role in immune modulation, particularly in reducing respiratory tract infections in deficient individuals. Effects are most pronounced when correcting deficiency rather than supplementing above adequate levels.
Moderate-to-weak evidence suggests vitamin D supplementation may modestly improve muscle strength in deficient individuals, but recent well-designed trials in vitamin D-replete populations show no benefit for muscle function, strength, or physical performance.
Weak evidence suggests vitamin D supplementation may modestly reduce depressive symptoms in people who are deficient, but it does not appear effective as a standalone treatment for clinical depression.
Moderate evidence from observational studies and some RCTs suggests vitamin D deficiency is associated with worse COVID-19 outcomes. Supplementation may reduce ICU admission and mortality in deficient patients, but effects in replete individuals are minimal.
Earlier meta-analyses suggested vitamin D supplementation reduces fracture risk, particularly at higher doses combined with calcium. However, the large VITAL randomized trial found no fracture reduction, creating significant conflict in the evidence base.
Earlier meta-analyses suggested vitamin K (particularly K2) reduces fracture risk, but a large 2019 BMJ trial found no benefit from vitamin K1 supplementation. The evidence is mixed, with potential benefits limited to vitamin K2 in specific populations.
Weak evidence against vitamin E for heart disease prevention. Despite promising observational data and biological plausibility, large RCTs (HOPE, ATBC, SELECT) consistently show no cardiovascular benefit from vitamin E supplementation. Some meta-analyses suggest high doses may slightly increase all-cause mortality.
Moderate evidence suggests vitamin K2 (menaquinone) may reduce arterial calcification by activating matrix Gla-protein, which inhibits calcium deposition in vessel walls. Observational data is strong, but RCT evidence remains limited and mixed.
Strong evidence shows zinc is essential for immune function and that supplementation reduces cold duration by 1-2 days when taken within 24 hours of symptom onset. Zinc deficiency clearly impairs immunity.
Moderate evidence supports zinc supplementation improving wound healing, primarily in zinc-deficient individuals. In those with adequate zinc status, supplementation shows minimal additional benefit. The strongest evidence exists for surgical wounds and chronic leg ulcers in populations at risk of deficiency.
Moderate evidence supports zinc carnosine (polaprezinc) for protecting and healing gut mucosa. It is approved in Japan for gastric ulcer treatment and shows promise for NSAID-induced gut damage and exercise-induced intestinal permeability, though large Western RCTs are limited.
Moderate evidence suggests ashwagandha (Withania somnifera) significantly reduces self-reported anxiety and stress symptoms compared to placebo, with effects comparable to some low-dose anxiolytics.
Creatine monohydrate is one of the most extensively studied sports supplements. Decades of research in healthy adults show no evidence of kidney, liver, or cardiovascular harm at recommended doses.