Regulates calcium and phosphate, bone mineralisation, and muscle and nerve function.
Switzerland age 18–65: 15 µg/day; age 65+: 20 µg/day. This assumes little endogenous production.
Oily fish, egg yolk and fortified foods; also made in skin through UVB exposure.
Rickets in children and osteomalacia in adults; bone pain and muscle weakness can occur.
Deficiency harms bone. High levels do not broadly prevent cancer, cardiovascular disease or weight problems in replete people.
Hair and nails do not reliably indicate vitamin D deficiency.
Low sun exposure, darker skin, older age, covering clothing, fat malabsorption and obesity.
For risk factors or symptoms, assess 25-OH-D in clinical context; thresholds differ among professional bodies.
Use according to Swiss guidance, risk group or confirmed deficiency; avoid blind megadosing.
Overdose can cause hypercalcaemia, kidney stones, arrhythmias and organ damage.