# item.guide
Side-by-Side Comparison Essential Vitamins & Minerals

Calcium (Elemental Ca) vs. Selenium (Elemental Se)

Comparing 2 standards across 9 specifications. 9 key differences identified.

Comparing:
Calcium (Elemental Ca)
Selenium (Elemental Se)

Calcium is the most abundant mineral in the human body (1.0–1.2 kg), with 99% sequestered in hydroxyapatite bone lattice and 1% tightly regulated at 8.5–10.5 mg/dL serum for cardiac contractility, nerve signaling, and blood coagulation. Adult RDA is 1,000–1,200 mg/day.

View full Calcium (Elemental Ca) spec sheet →

Selenium is an essential trace element incorporated as Selenocysteine (the 21st amino acid) into 25 human selenoproteins including Glutathione Peroxidases (GPx) and Iodothyronine Deiodinases (T4->T3 conversion). Adult RDA is 55 µg, with a Tolerable Upper Limit of 400 µg/day.

View full Selenium (Elemental Se) spec sheet →

Specification Comparison Table

9 Parameters
Parameter / Spec
Nutrient Type
Essential Macromineral Essential Trace Element
Adult RDA / RDI
1,000 mg / day (Men 19–70, Women 19–50) / 1,200 mg (Women 51+, Men 71+) 55 µg / day (60 µg pregnancy, 70 µg lactation)
Tolerable Upper Limit (UL)
2,500 mg / day (Adults 19–50) / 2,000 mg / day (Adults 51+) (Avoid nephrolithiasis / vascular calcification) 400 µg / day (Avoid selenosis / garlic breath, hair/nail brittleness)
Chemical Forms
Calcium Carbonate (40% elemental Ca / requires stomach acid), Calcium Citrate (21% elemental Ca / acid-independent), Hydroxyapatite Selenomethionine (Plant organic), Selenocysteine (Animal selenoprotein), Sodium Selenite / Selenate (Inorganic)
Primary Biological Function
Hydroxyapatite bone/dental structure [Ca10(PO4)6(OH)2], Troponin-C actin-myosin muscle contraction, Factor IV blood clotting cascade, Exocytosis neurotransmitter release Glutathione Peroxidase (GPx1-4) lipid hydroperoxide neutralization, Iodothyronine Deiodinases (Converts thyroid T4 into active T3), Thioredoxin Reductase (TXNRD)
Deficiency Condition
Osteoporosis, Osteopenia, Rickets (children), Tetany (Trousseau's and Chvostek's signs of hypocalcemia) Keshan Disease (Endemic juvenile cardiomyopathy), Kashin-Beck Disease (Deforming osteoarthropathy), Impaired thyroid metabolism
Top Whole Food Sources
Parmigiano-Reggiano, Sharp Cheddar, Whole Milk, Sardines with bones, Kale, Tofu (Calcium-set), Fortified Plant Milk Brazil Nuts (1 single nut provides ~70–90µg / 130–160% RDA), Eastern Oysters, Yellowfin Tuna, Halibut, Sardines, Beef Liver, Eggs
Parathyroid Hormone (PTH) Homeostasis
Serum Ca2+ drop triggers PTH secretion, stimulating renal 1-alpha-hydroxylase to produce active Calcitriol (1,25-OH-D3) and osteoclast bone resorption
Soil Selenium Geographical Variability
Plant selenium reflects regional soil content; volcanic soils (South America, Great Plains) are rich, while parts of China, Scandinavia, and New Zealand are depleted