Growing awareness that vitamin D insufficiency has serious health consequences beyond rickets and osteomalacia highlights the need for accurate assessment of vitamin D nutritional status. Although there is general agreement that the serum 25(OH)D level is the best indicator of vitamin D deficiency and sufficiency, the cutoff values have not been clearly defined. While laboratory reference ranges for serum 25(OH)D levels are often based on average values from populations of healthy individuals, recent research suggests that health-based cutoff values aimed at preventing secondary hyperparathyroidism and bone loss should be considerably higher. In general, serum 25(OH)D values less than 20-25 nmol/L indicate severe deficiency associated with rickets and osteomalacia. Although 50 nmol/L has been suggested as the low end of the normal range, more recent research suggests that PTH levels and calcium absorption are not optimized until serum 25(OH)D levels reach approximately 80 nmol/L . Thus, at least one vitamin D expert has argued that serum 25(OH)D values less than 80 nmol/L should be considered deficient, while another suggests that a healthy serum 25(OH)D value is between 75 nmol/L and 125 nmol/L. Data from supplementation studies indicates that vitamin D intakes of at least 800-1,000 IU/day are required by adults living in temperate latitudes to achieve serum 25(OH)D levels of at least 80 nmol/L.
 

The Adequate Intake (AI)

In 1997, the Food and Nutrition Board of the Institute of Medicine felt that the issue of sunlight exposure confounded the existing data on vitamin D requirements, making it impossible to calculate an RDA. Instead, the Food and Nutrition Board set adequate intake levels  that assume no vitamin D is being synthesized in the skin through exposure to sunlight. The AI values established in 1997 (see table below) reflect vitamin D intakes likely to maintain serum 25(OH)D levels of at least 37.5 nmol/L, which many experts now feel is too low.

Bee Pollen
 

Royal Jelly
 

Viagra