1000–2000 IU daily with a fatty meal (breakfast or lunch works well). If you've never had your levels tested, aim for the higher end; if deficient (<50 nmol/L), consider 4000 IU daily under GP guidance.

500–1000 mg daily in split doses (e.g., 500 mg with breakfast, 500 mg with dinner) for prevention. If you feel a cold coming on, increase to 1000 mg daily for 1–2 weeks. Powder or tablet forms both work; powder dissolves easily in water if you prefer.

15–30 mg daily, taken at the first sign of cold symptoms (scratchy throat, fatigue, sniffles). Lozenges are ideal because they dissolve slowly in the throat where the virus first takes hold. If using capsules, take with food to minimise nausea. Use for 1–2 weeks only during active illness.

500–1000 mg daily, taken with meals and ideally alongside vitamin C for better absorption. During cold season or if you're prone to respiratory infections, take 1000 mg daily. Can be used year-round or seasonally.