Clin Lab Med. 2000 Sep;20(3):569-90.
Calcium and vitamin D. Diagnostics and therapeutics.
Department of Medicine, Boston University School of Medicine, Massachusetts, USA.
Vitamin D is neither a vitamin nor a nutrient if adequate exposure to sunlight is available to produce adequate quantities of vitamin D3 in the skin. It is well known that an adequate supply of vitamin D, either from the diet or from the skin, is important for maximum bone health throughout life. The new revelation that 25(OH)D can be metabolized to 1,25(OH)2D in the colon, prostate, and skin opens a new chapter in the vitamin D story. It is quite possible that there are two levels of vitamin D sufficiency. One level requires that the serum 25(OH)D levels be at least 20 ng/mL to satisfy the body's requirement for the renal production of 1,25(OH)2D that regulates calcium absorption, and bone calcium mobilization and bone mineralization. The second level may need higher circulating levels of 25(OH)D for maximum cellular health because of the conversion of 25(OH)D to 1,25(OH)2D in extrarenal tissues, such as the prostate, colon, and skin.
American Journal of Clinical Nutrition, Vol. 69, No. 5, 842-856, May 1999
© 1999 American Society for Clinical Nutrition
Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety1,2
For adults, the 5-µg (200 IU) vitamin D recommended dietary allowance may prevent osteomalacia in the absence of sunlight, but more is needed to help prevent osteoporosis and secondary hyperparathyroidism. Other benefits of vitamin D supplementation are implicated epidemiologically: prevention of some cancers, osteoarthritis progression, multiple sclerosis, and hypertension.
Total-body sun exposure easily provides the equivalent of 250 µg (10000 IU) vitamin D/d, suggesting that this is a physiologic limit. Sailors in US submarines are deprived of environmentally acquired vitamin D equivalent to 20–50 µg (800–2000 IU)/d. The assembled data from many vitamin D supplementation studies reveal a curve for vitamin D dose versus serum 25-hydroxyvitamin D
[25(OH)D] response that is surprisingly flat up to 250 µg (10000 IU) vitamin D/d. To ensure that serum 25(OH)D concentrations exceed 100 nmol/L, a total vitamin D supply of 100 µg (4000 IU)/d is required. Except in those with conditions causing hypersensitivity, there is no evidence of adverse effects with serum 25(OH)D concentrations <140 nmol/L, which require a total vitamin D supply of 250 µg (10000 IU)/d to attain. Published cases of vitamin D toxicity with hypercalcemia, for which the 25(OH)D concentration and vitamin D dose are known, all involve intake of 1000 µg (40000 IU)/d. Because vitamin D is potentially toxic, intake of >25 µg (1000 IU)/d has been avoided even though the weight of evidence shows that the currently accepted, no observed adverse effect limit of 50 µg (2000 IU)/d is too low by at least 5-fold.
American Journal of Clinical Nutrition, Vol. 80, No. 6, 1706S-1709S, December 2004
© 2004 American Society for Clinical Nutrition
VITAMIN D AND HEALTH IN THE 21ST CENTURY: BONE AND BEYOND
Functional indices of vitamin D status and ramifications of vitamin D deficiency1,2,3,4
Robert P Heaney
1 From Creighton University Medical Center, Omaha
Serum 25-hydroxyvitamin D3 [25(OH)D3] concentrations are currently recognized as the functional status indicator for vitamin D. Evidence is reviewed that shows that serum 25(OH)D3 concentrations of < 80 nmol/L are associated with reduced calcium absorption, osteoporosis, and increased fracture risk. For typical older individuals, supplemental oral intakes of 1300 IU/d are required to reach the lower end of the optimal range. Evidence of substantial problems in routine clinical measurement of serum 25(OH)D3 concentrations among patients is cited. There is great need for standardization and improved reproducibility and sensitivity of measurements of serum 25(OH)D3 concentrations.
Vitamin D Linked With Neuromuscular Performance in the Elderly
Sept. 28, 2005 (Nashville) — Low serum levels of vitamin D in the body may make elderly persons more susceptible to falls, Netherlands researchers reported here at the American Society of Mineral and Bone Research (ASBMR) 27th annual meeting.
"Low levels of vitamin D were associated with low physical performance," said Ilse Wicherts, a doctorate student at Vu University Medical Center in Amsterdam, the Netherlands. "This study shows that neuromuscular performance in those with lower levels of vitamin D was significantly lower than those with adequate levels.
"These individuals already are fragile," added Ms. Wicherts, the winner of an ASMBR Young Investigator Award. "The lack of mobility places them at high risk of falls and fractures."
In the study 1,238 men and women (mean age, 75 years) by Ms. Wicherts and colleagues, a low serum level of vitamin D was associated with lower neuromuscular performance. The study was undertaken within the framework of the Longitudinal Aging Study Amsterdam (LASA).
Neuromuscular performance was measured by five chair stands for muscle strength, a walking test for balance, and tandem stand testing coordination and mobility where participants must stand with one foot in front of the other. Each performance test was scored in seconds and was classified with scores from 1 to 4 according to quartiles of distribution. The total performance score for muscle strength and balance ranged from 0 to 12. The researchers used a multivariate regression analysis adjusted for age, sex, and body mass index.
Eleven percent of the participants had serum vitamin D levels less than 25 nmol/L, 37% had levels between 25 and 50 nmol/L, 33% had levels between 50 and 75 nmol/L, and 17% had levels of 75 nmol/L or above.
Scores for chair stands, the walking test, and tandem stand each showed significant improvement with increased serum levels of vitamin D.
Participants with vitamin D at 25 nmol/L had a performance score of 4.9 while those with vitamin D levels between 25 and 50 nmol/L had scores of 6.82 and those with levels between 50 and 75 nmol/L had scores of 8.10. Participants with vitamin D levels of 75 nmol/L or higher had performance scores of 8.72.
"There was a linear progression," Ms. Wicherts said. "The change in performance scores with increasing serum 25(OH)D was significant for all steps."
When researchers adjusted for age, sex, body mass index, smoking, and alcohol consumption, the performance score increased significantly with serum vitamin D levels up to 50 nmol/L.
Performance was reduced 18% if the vitamin D levels were lower than 25 nmol/L compared with participants with levels of 75 nmol/L or higher and 5% if vitamin D levels were between 25 and 50 nmol/L after adjusting for other risk factors, Ms. Wicherts said.
"Persons with low serum vitamin D levels had a higher risk for low physical performance," Ms. Wiecherts told Medscape. "The strongest effects were found in persons with a major deficiency."
"This is a very important study because it suggests that vitamin D is not only important for bone health, but is important in neuromuscular stability," said Elizabeth Shane, MD, president-elect of ASBMR. "Bone fracture is due to not only bone issues, but issues contributing to falls.
"There is a two-pronged effect here that can increase the propensity for fractures in the elderly," Dr. Shane said. "Adequate Vitamin D can aid in improving muscle strength and preventing falls in this older age group."
ASBMR 27th Annual Meeting: Abstract 1134. Presented September 26, 2005.
Reviewed by Gary D. Vogin, MD