16.3: Vitamin D deficiency in humans (18b.3)
- Page ID
- 117075
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Osteomalacia may occur in severely vitamin D deficient adults, a condition characterized by a failure in the mineralization of the organic matrix of bone. This results in weak bones, diffuse skeletal bone tenderness, proximal muscle weakness, and an increased frequency of fractures. Such disturbances are associated with serum 25(OH)D concentrations below 7.5nmol/L (Haddad and Stamp, 1974). After treatment with vitamin D supplements, serum 25(OH)D values rise and radiological lesions heal (Preece et al., 1975). Osteomalacia prevalence may be high globally due to lack of sun exposure, but remains largely undiagnosed due to the need to have radiographic data (Uday and Högler, 2019). It may occur in adults living in the tropics,who have no sun exposure, such as garment factory workers in Bangladesh (Islam et al., 2008). Low dietary intake may also play a role. A study in Germany of mainly white adults who died accidently, found the prevalence of osteomalacia to be at least 25% based on osteoid volume/bone volume ratio (Priemel et al., 2010).
Some adult patients with chronic renal failure, gastrectomy, intestinal malabsorption and steatorrhea arising from celiac disease, inflammatory bowel disease, pancreatic insufficiency, or massive bowel resection, may also develop osteomalacia. Functional disturbances have been described in adults with low serum 25(OH)D concentrations. These include secondary hyperparathyroidism, an increased bone turnover, and reduced bone mass (Chapuy et al., 1997). In the elderly, suboptimal vitamin D status decreases absorption of calcium, a factor associated with a lowering of the bone mineral content during postmenopausal aging.
Rickets occurs in infants and children with severe vitamin D deficiency. In rickets, abnormal softness of the skull (craniotabes) occurs. This may be accompanied by enlargement of the epiphyses of the long bones and of the costochondral junction (rachitic rosary). Bowlegs and knock knees may arise from these bone deformities. Rickets, arising from primary vitamin D deficiency may occur in infants in industrialized countries who are breast-fed without vitamin D supplementation. A supplement of 400 IU (10µg) per day to prevent rickets is often recommended for all infants from birth to 12mo of age, independent of their mode of feeding (Wagner and Greer, 2008; Munns et al., 2016). However, for breastfed infants whose mothers have an adequate vitamin D status, the content of vitamin D in breastmilk can be sufficient because the vitamin D content in breastmilk is dependent on maternal status (Stoutjesdijk et al., 2017). Nutritional rickets can occur in older children, particularly during the adolescent growth spurt (Beck-Nielsen et al., 2009; Uday and Högler, 2019). However, some nutritional rickets is also caused by a lack of calcium, so both vitamin D and calcium should be monitored (Munns et al., 2016; Uday and Högler, 2019).
Metabolic defects also cause rickets, including both vitamin D-resistant rickets (familial hypophosphatemia) and vitamin D-dependent rickets (VDDR type 1). The latter condition is a deficiency of the 25(OH)2D-1-hydroxylase enzyme, while vitamin D-resistant rickets is a defect in proximal renal tubular resorption of phosphate. The yearly incidence of hypophosphatemic rickets in infants 0–0.9y is about 3.9 per 100,000: vitamin D-resistant rickets (VDDR type 1) is very rare (Beck-Nielsen et al., 2009).