| Property | Vitamin D | Calcium |
|---|---|---|
| Scientific name | Cholecalciferol (D3) | Calcium carbonate / citrate |
| Safety rating | Generally Safe | Conditionally Safe |
| Evidence level | Strong | Strong |
| Category | Fat-Soluble Vitamins | Major Minerals |
| RDA | 600 IU; 800 IU if >70y | 1,000 mg; 1,200 if >50y (F) |
| Tolerable UL | 4,000 IU | 2,500 mg |
| Clinical pearl | Check 25(OH)D in all at-risk patients (BMI >30, age >65, dark skin, northern latitude) [21]. D3 is 87% more potent than D2 at raising serum levels [4]. Prescribe with a fat-containing meal for optimal absorption [7]. Co-supplement with K2 (MK-7) for bone and vascular benefit [17]. Target 30–50 ng/mL; >50 rarely adds benefit and >150 risks toxicity [1][21]. Large bolus dosing (>300,000 IU) paradoxically increases falls — use daily/weekly dosing [11][25]. The VITAL trial showed no cancer or CVD prevention at 2,000 IU/day but did reduce autoimmune disease by 22% [12][13]. | Calcium is the cornerstone of skeletal health but only works in concert with vitamin D and vitamin K. Food sources are preferred over supplements. Calcium carbonate requires acid (take with meals); calcium citrate does not (ideal for PPI users and post-bariatric patients). Never exceed 500 mg per dose [1] [5]. |
| Key interactions | See profile | See profile |
| US products (DSLD) | 3,552 | 7,096 |