Essential for Maintaining Healthy Bone Growth and Density Dietary Supplement Vitamin D3 can be synthesized by humans in the skin upon exposure to ultraviolet-B (UVB) radiation from sunlight. But, due to the winter season, weather conditions, and sun block, the body’s ability to produce optimal vitamin D levels may be inhibited. These factors point to the value of taking a daily vitamin D supplement. Vitamin D has long provided significant support for healthy bone density. However, scientists have also validated the critical role that vitamin D plays in regulating healthy cell division and differentiation, and its profound effects on human immunity. These findings link a deficiency of vitamin D to a host of common age-related problems. The current RDA for vitamin D is only 600 IU which has resulted in startling evidence of a widespread deficiency for this vitamin. Most experts in the field now recommend intakes between 1,000 - 10,000 IU for adults to achieve a serum 25(OH)D level above those indicative of vitamin D deficient levels, at approximately 80 nmol/L or 32 ng/ml. Life Extension suggests that healthy adults supplement each day with 5000-8000 IU of vitamin D with the objective of achieving an optimal 25-hydroxy vitamin D blood level between 50-80 ng/ml. A vitamin D blood test can help you determine the amount of vitamin D you need to supplement with to achieve an optimal level.