It can take anywhere from 1-6 months to raise vitamin D levels with supplements. How much your levels increase and how long it takes will depend on the dose and your baseline vitamin D levels. Factors such as age, weight, skin pigmentation, genetics, physical activity level, and sun exposure also impact the effectiveness and absorption of supplemental vitamin D. If you have very low vitamin D (<20 ng/mL), you will likely require more vitamin D supplementation to achieve an optimal level for good health (>40 ng/mL).
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If your baseline vitamin D level is at or below 40 ng/mL, moderate daily supplementation of 1,000-5,000 IU vitamin D3 (cholecalciferol) may be appropriate, however, you should talk with a dietitian or your doctor to find the right dosage.