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Vitamin D

Supplement vitamin bone & jointimmune
Aka: vitamin d3, cholecalciferol, calciferol
Brands seen in Singapore: Kordel's, Caltrate
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
Calcium absorption and bone health · low sun or low levels
When to take
With a meal · fat in the gut raises absorption
Take with
Food with some fat · calcium combos may add side-effect risk
Pros & cons
Pros
  • RDA 600 IU (15 mcg) a day; 800 IU over 70
  • D3 raises blood levels more, and longer, than d2
  • Low sun, dark skin, older age = listed risk groups
Cons
  • UL 4,000 IU (100 mcg) a day; excess is toxic
  • Toxicity is almost always from supplements, not sun
  • Excess → high calcium: nausea, weakness, kidney stones
Sources
  1. NIH ODS — Vitamin D Fact Sheet for Health Professionals (updated Jun 27, 2025) · read 2026-08-27
    what it says
    “Vitamin D (also referred to as calciferol) is a fat-soluble vitamin … Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal bone mineralization … The concurrent presence of fat in the gut enhances vitamin D absorption, but some vitamin D is absorbed even without dietary fat … most evidence indicates that vitamin D3 increases serum 25(OH)D levels to a greater extent and maintains these higher levels longer than vitamin D2 … Levels of 50 nmol/L (20 ng/mL) or more are sufficient for most people … Vitamin D toxicity is almost always a result of excessive intakes of vitamin D through supplements … Experts do not believe that excessive sun exposure results in vitamin D toxicity … Taking calcium supplements in combination with vitamin D supplements may increase the risk of certain adverse effects … Excess amounts of vitamin D are toxic … Hypercalcemia, in turn, can lead to nausea, vomiting, muscle weakness, neuropsychiatric disturbances, pain, loss of appetite, dehydration, polyuria, excessive thirst, and kidney stones … The weight-loss drug orlistat (Xenical and alli), together with a reduced-fat diet, can reduce the absorption of vitamin D from food and supplements … high intakes of vitamin D, especially from supplements, might reduce the potency of atorvastatin (Lipitor), lovastatin (Altoprev and Mevacor), and simvastatin (FloLipid and Zocor) … Corticosteroid medications, such as prednisone … can reduce calcium absorption and impair vitamin D metabolism … The combination of these diuretics with vitamin D supplements (which increase intestinal calcium absorption) might lead to hypercalcemia, especially among older adults and individuals with compromised renal function or hyperparathyroidism”
  2. FDA — Daily Value on the Nutrition and Supplement Facts Labels, Reference Guide: Daily Values for Nutrients (content current as of 03/05/2024) · read 2026-08-27
    what it says
    “DVs are the recommended amounts of nutrients to consume or not to exceed each day … Vitamin D 20mcg”
  3. HSA — Health Supplements Guidelines GL-CHPB-3-001 Rev. 020 (January 2026), s4.8, Table 4 Vitamins Limits + List of Health Claims · read 2026-08-27
    what it says
    “HS for use by the general adult population should not contain vitamins and minerals exceeding the stipulated limits stated in Tables 4 and 5 … Table 4: Vitamins Limits … Vitamin D 0.025mg (1000IU) … Help in the absorption and use of calcium and phosphorus • Vitamin D … Maintain/support bone health • Vitamin D, K”
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Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.