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Vitamin D has long provided significant support for healthy bone density.74-82 However, scientists have validated the critical role that vitamin D plays in regulating healthy cell division and differentiation, and has profound effects on human immunity.83* These findings link a deficiency of vitamin D to a host of common age-related problems. As a result of this research and startling evidence of a widespread vitamin D deficiency, prominent nutritional scientists are calling on Americans to increase their vitamin D intake to 1000 IU per day and higher. The current RDA is only 400 IU.

Vitamin D is synthesized in the body from sunlight. But, due to the winter season, weather conditions, and sunscreen blockers, the body’s ability to produce optimal vitamin D levels may be inhibited.84 In fact, it has been proposed that annual fluctuations in vitamin D levels explain the seasonality of influenza.85 All of these factors point to the value of taking a daily vitamin D supplement to ensure optimal vitamin D intake.

For those who need to take very high doses of vitamin D3 and are under a physician’s supervision, Life Extension offers a 5000 IU vitamin D3 supplement.

Large doses (1400-2000 IU/day) may cause hypercalcemia, a decrease in renal function, and nephro-calcinosis. Monthly blood tests to monitor serum calcium and parathyroid hormone levels should be done to protect against vitamin D3 toxicity. Those with underlying kidney disease should avoid high doses of vitamin D3. Although some research indicates that dosages up to 10,000 IU/day are safe, healthy people should stay below 2000 IU/day.