Giraffe
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I found two studies that checked levels of vitamin-D metabolites after supplementation or after UV radiation. Both studies confirm that 1,25(OH)2D is tightly regulated. As it is substrate depending during vitamin-D deficiency, an increase is seen in those subjects that were vitamin D-deficient before supplementation or radiation.
The Effect of Vitamin D Supplementation on Vitamin D Status and Parathyroid Function in Elderly Subjects
In this Dutch study, people living in nursing homes and aged people's homes were either supplemented for one year with 400 or 800 IU vitamin D3 daily or served as controls. The supplemented group reached levels in the vicinity of what by the majority of researchers is considered as needed to suppress PTH levels.
The next figure shows the individual serum 1,25-(OH)2D responses after 3 months of treatment with vitamin D3 (400 or 800 IU daily). Please note that this study was published in 1988; what they call "adequate" is just enough to prevent rickets and osteomalacia. **
Vitamin-D Synthesis and Metabolism after Ultraviolet Irradiation of Normal and Vitamin-D-Deficient Subjects
Eight healthy, white, paid volunteers received whole-body exposure equal to one to four times the minimal erythemal dose of UVR, and three vitamin-D-deficient white women received one minimal erythemal dose.
Interesting here is that 25(OH)D raises only moderately and slowly in the vitamin-D replete subjects although the vitamin D3 levels spike after UV radiation, especially in those who received a sunburn dose.
open triangles, dashed line = 3 vitamin-D deficient patients exposed to 1 MED (minimum erythemal dose)
solid squares, solid line = 3 healthy subjects exposed to 3 MED
solid circle, solid line = 1 healthy control exposed to 1 MED
_____
** Epidemic influenza and vitamin D (2006)
A paper written by several renowned researchers:
Estimates of optimal vitamin D status (2005)
The Effect of Vitamin D Supplementation on Vitamin D Status and Parathyroid Function in Elderly Subjects
In this Dutch study, people living in nursing homes and aged people's homes were either supplemented for one year with 400 or 800 IU vitamin D3 daily or served as controls. The supplemented group reached levels in the vicinity of what by the majority of researchers is considered as needed to suppress PTH levels.
The next figure shows the individual serum 1,25-(OH)2D responses after 3 months of treatment with vitamin D3 (400 or 800 IU daily). Please note that this study was published in 1988; what they call "adequate" is just enough to prevent rickets and osteomalacia. **
Vitamin-D Synthesis and Metabolism after Ultraviolet Irradiation of Normal and Vitamin-D-Deficient Subjects
Eight healthy, white, paid volunteers received whole-body exposure equal to one to four times the minimal erythemal dose of UVR, and three vitamin-D-deficient white women received one minimal erythemal dose.
Interesting here is that 25(OH)D raises only moderately and slowly in the vitamin-D replete subjects although the vitamin D3 levels spike after UV radiation, especially in those who received a sunburn dose.
open triangles, dashed line = 3 vitamin-D deficient patients exposed to 1 MED (minimum erythemal dose)
solid squares, solid line = 3 healthy subjects exposed to 3 MED
solid circle, solid line = 1 healthy control exposed to 1 MED
_____
** Epidemic influenza and vitamin D (2006)
_____The critical question of ‘What is an ideal 25(OH)D level?’ must be answered, ‘In regard to what?’ Levels needed to prevent rickets and osteomalacia (10 ng/ml) are lower than those that dramatically suppress parathormone levels (20 ng/ml) [105]. In turn, those levels are lower than those needed to increase intestinal calcium absorption maximally (34 ng/ml) [106]. In turn, neuromuscular performance in 4100 elderly patients steadily improved as 25(OH)D levels increased and maximum performance was associated with levels of 50 ng/ml [107]. If levels of 50 ng/ml are associated with further benefits, such as preventing viral respiratory infections, we are only now learning about it. Until more is known, it may be prudent to maintain wintertime 25(OH)D at concentrations achieved in nature by summertime sun exposure (50 ng/ml).
A paper written by several renowned researchers:
Estimates of optimal vitamin D status (2005)
Abstract
Vitamin D has captured attention as an important determinant of bone health, but there is no common definition of optimal vitamin D status. Herein, we address the question: What is the optimal circulating level of 25-hydroxyvitamin D [25(OH)D] for the skeleton? The opinions of the authors on the minimum level of serum 25(OH)D that is optimal for fracture prevention varied between 50 and 80 nmol/l. However, for five of the six authors, the minimum desirable 25(OH)D concentration clusters between 70 and 80 nmol/l. The authors recognize that the average older man and woman will need intakes of at least 20 to 25 mcg (800 to 1,000 IU) per day of vitamin D(3 )to reach a serum 25(OH)D level of 75 nmol/l. Based on the available evidence, we believe that if older men and women maintain serum levels of 25(OH)D that are higher than the consensus median threshold of 75 nmol/l, they will be at lower risk of fracture.
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