It feels like companies introduce a new kind of vitamin D supplement every month or so. We started with capsules, then came drops and now there are even lozenges. There’s a wide range of vitamin D dosages, typically from 400 IU to 10,000 IU. Someone with documented vitamin D deficiency will need at least 5,000 IU daily for at least three months to normalize blood levels. Do pay attention to product expiration dates—vitamin D does degrade faster than most other vitamins.