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.70 In fact, it has been proposed that annual fluctuations in vitamin D levels explain the seasonality of influenza.71 All of these factors point to the value of taking a daily vitamin D supplement.

Vitamin D has long provided significant support for healthy bone density.72-77 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.78-81 These findings link a deficiency of vitamin D to a host of common age-related problems.

The current RDA is only 600 IU. As a result of startling evidence of a widespread vitamin D deficiency, prominent nutritional scientists are calling on Americans to increase their vitamin D intake to 1,000 IU per day and higher. Currently, most experts in the field believe that intakes of between 1,000 and 10,000 IU for adults will lead to serum 25(OH)D levels above those indicative of vitamin D deficient levels, at approximately 80 nmol/L or 32 ng/mL.

Life Extension recommends that healthy adults supplement each day with at least 2,000 IU of vitaminD. Elderly adults may benefit from higher doses such as 5,000 IU daily up to 10,000 IU daily. The objective of taking a vitamin D supplement is to achieve an optimal 25-hydroxy vitamin D blood level of 50 ng/mL (and higher). Life Extension’s analysis of over 13,000 vitamin D blood tests reveals that the minimum intake for most aging people should be around 7,000 IU a day. Some individuals (such as those weighing over 180 pounds) may require higher potencies of vitamin D.

Individuals consuming more than 2,000 IU/day of vitamin D (from diet and supplements) should periodically obtain a serum 25-hydroxy vitamin D measurement. Do not exceed 10,000 IU per day unless recommended by your doctor. Vitamin D supplementation is not recommended for individuals with hypercalcemia (high blood calcium levels). People with kidney disease, certain medical conditions (such as hyperparathyroidism or sarcoidosis), and those who use cardiac glycosides (digoxin) or thiazide diurectics should consult a physician before using supplemental vitamin D.