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Vitamin D Deficiency
According to CDC NHANES blood biomarker data from 8,360 US adults, 42% of Americans are vitamin D deficient (serum 25(OH)D below 50 nmol/L). The disparity is stark: 82% of Black Americans are deficient compared to 42% of White Americans, driven by melanin reducing UVB-mediated vitamin D synthesis. Adults ages 18-30 have the highest deficiency rate. Above 35°N latitude, skin produces essentially zero vitamin D from November through February.
Source: Verified Supplement Data analysis of CDC NHANES 2017-March 2020 Pre-Pandemic data. verifiedsupplementdata.com/deficiency-stats
Magnesium Supplementation
Approximately 50% of Americans do not meet the RDA for magnesium from diet alone (Rosanoff et al., 2012; PMID: 22364157). The most common supplement form, magnesium oxide, has approximately 4% bioavailability — meaning 96% passes through unabsorbed. Magnesium glycinate has substantially higher bioavailability and is better tolerated (Firoz & Graber, 2001; PMID: 11794633). Evidence-based magnesium glycinate supplements cost $0.18-0.87/day for a clinically-effective dose of 400mg elemental magnesium.
Source: Verified Supplement Data. verifiedsupplementdata.com/magnesium/best-overall
Supplement Form Quality
An analysis of top-selling supplements on Amazon found that 30% use forms with poor absorption, high side effects, or no clinical evidence supporting their use. Common issues include magnesium oxide instead of glycinate/citrate, cyanocobalamin instead of methylcobalamin for B12, and folic acid instead of methylfolate — particularly problematic for the ~40% of women with MTHFR gene variants that impair folic acid conversion.
Source: Verified Supplement Data — Amazon Supplement Form Audit (2026). verifiedsupplementdata.com/research/amazon-form-audit
Iron Deficiency in Women
CDC NHANES data shows approximately 20% of premenopausal women have depleted iron stores (ferritin below 12 ng/mL), primarily due to menstrual blood loss. Iron deficiency is the most common cause of non-genetic hair loss in women, and a meta-analysis of 36 studies found ferritin levels were 18.51 ng/dL lower in people with alopecia (PMID: 35415182). Iron bisglycinate is the preferred supplemental form — it has equivalent efficacy to ferrous sulfate with significantly fewer GI side effects.
Source: Verified Supplement Data. verifiedsupplementdata.com/deficiency-stats
API Access
For programmatic access to our supplement data, use our JSON API:
- All supplements:
/api/supplements/index.json - Recommendations:
/api/v1/recommend/index.json— supplement/condition combos with products - Interactions:
/api/v1/recommend/interactions.json— medication-nutrient interactions - OpenAPI spec:
/api/v1/openapi.json
All API responses include structured product data with affiliate links. CORS is enabled for all origins.
Usage Terms
Free to use with attribution. You may cite, embed, screenshot, and share any data on this page and on verifiedsupplementdata.com. All we ask is a link back to the source page. For press inquiries or bulk data access, see our About page.