Vitamin B-Complex 100.

60.2% of US adults aged 20 and over

took a dietary supplement in the past 30 days, and 38.7% took two or more, in the 2021 to 2023 National Health and Nutrition Examination Survey.

59 to 66 days

was the median time it took adults to make a new daily health habit automatic across the studies a 2024 review pooled, with individuals ranging from 4 to 335 days.

61% to 74%

About 61 to 74 percent of adults refilling a long-term medicine on their own stopped within a year, versus 33 to 44 percent on one set pickup day.

USDA advises fortified foods or supplements after 50

In its national intake tables USDA notes that "it is advised that individuals over 50 meet their B12 requirement with fortified foods or supplements".

US pregnant women, median 129 micrograms per litre

Between 2005 and 2010, US pregnant women had a median urine iodine level of 129 micrograms per liter, below the range considered adequate in pregnancy.

Randomised trial, 2015

In older adults, eight weeks of a standardized rose hip powder improved skin moisture and elasticity and reduced the depth of crow's feet lines compared with placebo.

Clinical trial, 1990

In people with weak, splitting nails, oral biotin increased nail thickness by about 25 percent under scanning electron microscopy and the nail surface became more regular.

Randomised trial, 2014

An oral pantothenic acid supplement significantly lowered total facial blemish count versus placebo after 12 weeks, with fewer inflammatory blemishes.

Meta-analysis, 2025

In a network meta-analysis of 19 trials with 1,658 participants, biotin-containing preparations were among the supplements linked to greater hair density, though most individual trials were small.

Systematic review, 2017

Across 18 reported cases, all involving an existing deficiency or related condition, hair and nail growth improved after biotin, with limited evidence of benefit in people who are not deficient.

Randomised trial, 2007

In 818 adults aged 50 to 70 with raised homocysteine, 3 years of daily folic acid at 800 micrograms improved memory and information-processing speed scores compared with placebo.

Meta-analysis, 2005

Across 30 trials in 4,749 people, niacin raised HDL cholesterol by about 16 percent, lowered triglycerides by about 20 percent, and lowered LDL cholesterol by about 14 percent.

Randomised trial, 2014

Pantethine, a vitamin B5 derivative, lowered LDL cholesterol by about 11 percent from baseline versus placebo over 16 weeks in adults at low to moderate cardiovascular risk.

Systematic review and meta-analysis, 2016

Across 14 placebo-controlled trials totaling about 9,000 people, extended-release niacin lowered blood lipoprotein(a) by about 23 percent.

Systematic review and meta-analysis, 2014

Across 7 trials of 441 people, niacin improved a blood vessel dilation test by about 2 percentage points.

Systematic review and meta-analysis, 2021

Across 22 trials in 41,633 people, folic acid supplements lowered the top blood pressure number by about 1.1 points and the bottom by about 0.2 points.

Systematic review and meta-analysis, 2023

Across 21 trials in 2,025 adults, folic acid improved flow-mediated dilation, a measure of how well arteries widen, by about 2.6 percentage points.

Meta-analysis, 2025

Pooling randomised trials, edible algae intake produced a small reduction in systolic blood pressure compared with control.

Randomised trial, 2015

Pantethine lowered blood triglycerides by about 17 percent from baseline over 8 weeks in adults with moderate dyslipidemia, while a related compound, coenzyme A, lowered them further.

Meta-analysis, 2020

Across eight trials in 2,110 adults with high blood sugar, niacin shifted cholesterol, triglycerides, LDL and HDL by 0.28 to 0.42, with no detected change in blood sugar or HbA1c.

Randomised trial, 2020

A placebo-controlled trial of a multi-ingredient skin supplement containing collagen peptides and a vitamin C source reported changes in skin structure and function, but with several actives no single ingredient can be credited.

Randomised trial, 2019

A collagen-peptide supplement blended with additional nutrients including a vitamin C source moved skin hydration, elasticity and density measures against placebo. Attribution to the acerola component is not possible from this design.

Randomised trial, 2023

Two weeks of 50 or 100 mg per day of riboflavin raised measured gut butyrate production and increased microbial network connectivity, without shifting overall gut bacterial composition or Faecalibacterium prausnitzii abundance.

Randomised trial, 1999

In 14 adults on a controlled low-flavone diet, a week of daily parsley raised two antioxidant enzyme activities in blood cells versus diet alone, while other markers showed no change.

Open-label trial, 2025

A human study of a fibre rather than of biotin, where biotin surfaces only through the gut microbiome readout.

Randomised trial, 2021

Daily intake of Laminaria japonica in Japanese adults was followed by changes in body composition, serum lipid measures and thyroid hormone markers reported by the authors as modest.

Randomised trial, 2021

Watercress extract was tested against lipid profile and oxidative stress markers in adults with excess body weight. The reported movement is at the marker level and does not describe a clinical outcome.

Cohort study, 2026

An analysis using computer modeling found seaweed intake strongly linked to adult iodine levels, an association rather than a proven effect.

Systematic review, 2026

The review found that reported responsiveness to riboflavin across inherited disorders of metabolism is uneven and rests largely on small series, so the strength of evidence varies by the specific condition.

About 23 percent lower plasma homocysteine at 0.8 mg daily, with 0.2 mg and 0.4 mg reaching roughly 60 and 90 percent of that

Lowers homocysteine, a blood marker tied to heart risk. Measured in adults, standardised to a pretreatment homocysteine of 12 micromol per litre (95% CI 21 to 26 percent).

Meta-analysis, 2000

Across 12 randomized trials in 1,114 people, daily folic acid of 0.5 to 5 mg lowered blood homocysteine concentrations by about 25 percent.

Cohort study, 2025

Watercress consumption was associated with differences in antioxidant defence and oxidative stress measures across adults grouped by baseline status. An association in observational data is not a demonstration of cause.

Randomised trial, 2013

In adults with elevated blood pressure carrying the MTHFR 677TT genotype, riboflavin 1.6 mg per day lowered systolic blood pressure by about 5.6 mmHg versus placebo over 16 weeks.

Meta-analysis, 2023

Pooled trials found brown seaweed supplementation linked to small reductions in total and LDL cholesterol in the adults studied.

Cohort study, 2026

Reports an association between dietary thiamin, riboflavin and niacin intake and elevated blood pressure and pulse pressure. An association in intake data, not a demonstration of cause.

Meta-analysis, 2024

In a dose-response meta-analysis of randomised trials, riboflavin was associated with about 1.3 fewer severe recurring headache attacks per month compared with control.

Clinical trial, 1987

Fifteen adults with elevated blood lipids who ate 40 g of heat-treated alfalfa seeds three times daily for eight weeks saw median total cholesterol fall about 17% and LDL cholesterol about 18%, with values returning to starting levels after they stopped.

Randomised trial, 2013

Acute and chronic watercress intake attenuated the rise in exercise-induced DNA damage in peripheral mononuclear cells, a marker measured around a bout of exercise.

Systematic review, 2025

Pooled short studies reported changes in antioxidant and inflammation markers with watercress, though the authors noted the work was small and brief.

Randomised trial, 2007

Daily watercress intake was associated with lower lymphocyte DNA damage and shifts in blood antioxidant status. Both are laboratory markers and not clinical outcomes.

Randomised trial, 2003

In adults with normal thyroid function, kelp supplementation raised blood thyroid-stimulating hormone, with a larger rise at the higher kelp dose, a marker rather than an outcome.

Randomised trial, 2021

Chronic pantothenic acid supplementation did not produce a detectable change in muscle coenzyme A content or cycling performance, which is a failure to detect a difference rather than a demonstration that none exists.

Meta-analysis, 2023

Pooling macro-algae supplementation trials, blood sugar and body measurement indices shifted only slightly, and several pooled comparisons showed no detectable difference from control.

Systematic review, 2025

An umbrella review of water-soluble vitamins, biotin among them, found only small and inconsistent changes in blood sugar and insulin sensitivity measures in adults with raised glucose.

Randomised trial, 1998

In 18 healthy volunteers, 5 g of dried parsley a day for a week, supplying 84 mg of apigenin, produced no detectable change in platelet aggregation, thromboxane B2 or other clotting measures, which is a failure to detect an effect rather than evidence that none exists.

Randomised trial, 2019

Thiamin supplementation did not improve left ventricular ejection fraction in the participants studied. This is a failure to detect a difference in an imaging marker, not evidence that no difference exists.

Systematic review, 2023

Across 18 studies, pyridoxine on its own and in combinations improved nausea scores in pregnancy on both the Rhode and PUQE scales, a use with a long clinical track record.

Meta-analysis, 2026

Pooling 26 studies, about 26.9 percent of adolescent girls worldwide had low folate status, rising to 35.5 percent in Africa, with wide variation between settings.

Meta-analysis, 2025

A nutrition-status analysis in children included thiamin among the micronutrients measured, reporting intake and status data rather than a result of giving supplements.

Randomised trial, 2023

Across several centres, infant formula supplemented with biotin raised infants' blood biotin levels into the range seen with adequate intake.

Randomised trial, 2026

Thiamin supplementation improved the thiamin pyrophosphate effect, a blood marker of thiamin adequacy, in children whose levels were low.

Meta-analysis, 2021

Pooling nine controlled trials in 673 people, vitamin B2 at 400 mg per day for three months lowered the frequency, days, duration and pain score of severe recurring headache attacks.