Overview

• Authorities and clinicians warn that toxicity stems from excessive supplements, not sunlight or normal food, with risks including hypercalcaemia and kidney damage.
• Because 25‑OH‑vitamin D has a half‑life of roughly 10–40 days, levels typically take 20–80 days to fall after an overdose and may take months to normalize.
• Experts favor lower daily intake over intermittent high bolus doses; EFSA sets a tolerable upper level at 4,000 IU/day and higher therapeutic regimens should be medically supervised.
• Dosing is individualized by baseline level and body weight, with a reported rule of thumb that 10,000 IU raises serum 25‑OH‑D by about 1 ng/ml.
• A DKFZ review of trials suggests daily vitamin D3 did not prevent cancer but was associated with a 12% reduction in cancer mortality, whereas high intermittent doses showed no effect.