Vitamin D inadequacy in Belgian postmenopausal osteoporotic women
Reported, January 12, 2012
Methods
Assessment of 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone was performed in 1195 Belgian postmenopausal women aged over 50 years. Main analysis has been performed in the whole study population and according to the previous use of vitamin D and calcium supplements. Four cut-offs of 25(OH)D inadequacy were fixed : < 80 nmol/L, <75 nmol/L, < 50 nmol/L and < 30 nmol/L.
Results
Mean (SD) age of the patients was 76.9 (7.5) years, body mass index was 25.7 (4.5) kg/m2. Concentrations of 25(OH)D were 52.5 (21.4) nmol/L. In the whole study population, the prevalence of 25(OH)D inadequacy was 91.3 %, 87.5 %, 43.1 % and 15.9% when considering cut-offs of 80, 75, 50 and 30 nmol/L, respectively. Women who used vitamin D supplements, alone or combined with calcium supplements, had higher concentrations of 25(OH)D than non-users. Significant inverse correlations were found between age/serum PTH and serum 25(OH)D (r = -0.23/r = -0.31) and also between age/serum PTH and femoral neck BMD (r = -0.29/r = -0.15). There is a significant positive relation between age and PTH (r = 0.16), serum 25(OH)D and femoral neck BMD (r = 0.07). (P < 0.05)
Vitamin D concentrations varied with the season of sampling but did not reach statistical significance (P = 0.09).
Conclusion
This study points out a high prevalence of vitamin D inadequacy in Belgian postmenopausal osteoporotic women, even among subjects receiving vitamin D supplements.
Osteoporosis is a chronic, progressive disease characterized by reduced bone mass and microarchitectural deterioration of bone, involving an extensive fragility and a subsequent increase in fracture risk .
Vitamin D and calcium are essential components of osteoporosis management. Once vitamin D is absorbed from the diet or synthetised in the skin by the action of sunlight, it is metabolized first in liver to 25-hydroxyvitamin D [25(OH)D] and then in kidney to 1,25-dihydroxyvitamin D [1,25(OH)2D], before becoming biologically active. Then, 1,25(OH)2D interacts with its nuclear receptor (VDR) in target tissues where appropriate biological responses are mediated, in particular to maintain calcium homeostasis by increasing efficiency of intestinal calcium absorption . As a consequence, decreasing 25(OH)D serum concentrations leads to reduced calcium absorptive performance yielding to an increase in PTH concentrations. This leads to an increased bone resorption and accelerated bone loss, by increasing the number and activity of osteoclasts that release calcium from bone. Decreasing bone mineral density (BMD) and bone strength with increased susceptibility to fragility-fracture risk are ultimate consequences of vitamin D deprivation . Vitamin D inadequacy has also been implicated as a contributing factor to muscle weakness and propensity to fall, both in active and inactive ambulatory elderly subjects . A positive relationship has also been shown between cognitive functioning and vitamin D concentrations, which may also influence the risk of fall and fracture .
Sunlight and diet are the two sources of vitamin D. UV-B irradiation is the primary source of vitamin D. Approximately 90% of serum vitamin D is produced endogenously from 7-dehydrocholesterol in the epidermis of the skin, after adequate exposure. However, the capacity of the skin to produce vitamin D declines with aging . Moreover, environmental factors influence the cutaneous production of vitamin D. Latitude, season, and time of day as well as ozone pollution in the atmosphere diversify the number of solar ultraviolet B photons reaching the earth’s surface, and thereby, alter the cutaneous production of vitamin D3 .
As a consequence, in the light of the implication of vitamin D deficiency in bone metabolism, osteoporosis prevention guidelines developed by scientific authorities contain recommendations for vitamin D intake and evidence-based treatment of osteoporosis requires vitamin D supplements to maintain adequate plasma concentration .
The objective of this study is to assess the prevalence of inadequate serum vitamin D concentrations in postmenopausal Belgian women.
This study points out a high prevalence of vitamin D inadequacy in Belgian postmenopausal osteoporotic women even among subjects receiving vitamin D supplements. More studies are needed to address the amount of vitamin D intake necessary to maintain serum 25(OH)D to an adequate concentration which prevents secondary hyperparathyroidism and minimizes the possibility of further bone loss.
Credits: Audrey Neuprez, Olivier Bruyère, Julien Collette and Jean-Yves Reginster.
More information:
http://www.biomedcentral.com/1471-2458/7/64