#Vitamin D
How much vitamin D you need, AAP and EFSA guidance for kids and adults, signs of deficiency and toxicity, when to test 25(OH)D blood levels.
Vitamin D is a fat-soluble hormone-vitamin synthesised in skin on sun exposure and obtained from a few dietary sources (oily fish, fortified dairy, egg yolks). Roughly one in three adults in Central Europe is insufficient, with rates higher in winter and at northern latitudes.
Doses. The US RDA is 600 IU (15 µg) daily for most adults and 800 IU after 70. Deficient adults often need 1000-2000 IU daily for repletion, ideally guided by a 25-hydroxyvitamin D blood test. AAP recommends 400 IU daily for breastfed infants from the first days of life. EFSA paediatric Tolerable Upper Intake Levels: 50 µg/day for 1-10 years, 100 µg/day for 11+.
Forms. Vitamin D3 (cholecalciferol) is the form produced by sun on skin and the form recommended in most clinical guidance. D2 (ergocalciferol) is the form usually prescribed at very high pharmacological doses and is plant-derived.
Safety. Hypervitaminosis D is rare under 4000 IU/day in adults but possible with chronic mega-dosing — symptoms include nausea, weakness, frequent urination, hypercalcaemia. Always pair high-dose supplementation with periodic blood testing.
On HealthyHerbology we cover vitamin D across paediatric AAP/NHS guidance, women's bone-health and pregnancy considerations, and men's testosterone-adjacent supplementation.
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Frequently asked about Vitamin D
- How much vitamin D should I take daily?
- The US RDA is 600 IU for most adults and 800 IU after 70. The EFSA paediatric Tolerable Upper Intake Level is 2000-4000 IU/day depending on age. A blood test (25-hydroxyvitamin D) is the only way to dose precisely.
- Should babies take vitamin D?
- AAP recommends 400 IU/day of vitamin D for all breastfed and partially breastfed infants from the first days of life. Formula-fed infants consuming at least 32 oz of vitamin-D-fortified formula generally meet the requirement.
- What are the signs of vitamin D toxicity?
- Hypervitaminosis D from over-supplementation can cause nausea, vomiting, weakness, frequent urination and ultimately hypercalcaemia. It is rare below 4000 IU/day in adults but possible with chronic mega-dosing.