145- What are the non-osseous effects of vitamin D?
Vitamin D plays an important role in the maintenance of bone health. In addi-
tion, it also has been demonstrated to have various non-osseous effects, which
include improvement of muscle strength and cardiovascular health, modulation
of immune system and glucose–insulin homeostasis, and antiproliferative
effects on various tissues including breast, prostate, and colon. Although the
role of vitamin D in muscle function is well established, data regarding other
non-osseous benefits are not so robust.- How does vitamin D deficiency cause myopathy?
Proximal myopathy is one of the common manifestations of vitamin D defi-
ciency, although it is more common in children than in adults. Vitamin D is
required for ATP-dependent calcium uptake into sarcoplasmic reticulum,
synthesis of muscle proteins (e.g., actin, troponin), and differentiation of
myogenic stem cells into myoblasts. Further, vitamin D deficiency has been
shown to be associated with atrophy of type 2 muscle fibers. Concurrent
hypophosphatemia associated with vitamin D deficiency also contributes to
myopathy. Secondary hyperparathyroidism consequent to vitamin D defi-
ciency also adds to proteolysis and atrophy of type 2 muscle fibers.
Therefore, patients with vitamin D deficiency manifest with reduced muscle
strength and increased tendency to fall. The latter is due to atrophy of type
2 muscle fibers as these fast-twitching fibers need to be recruited on sudden
change of posture to prevent a fall. Treatment with vitamin D (cholecalcif-
erol) has been shown to improve muscle strength and reduce the incidence
of falls.- What is metabolic bone disease?
Metabolic bone disease refers to heterogeneous group of disorders character-
ized by abnormalities of bone mineral metabolism, bone cells, or matrix.- What is growth plate?
The growth plate, also known as physis, is present between the epiphysis and
metaphysis at the ends of long bones. It comprises of five zones: resting zone,
proliferative zone, hypertrophic zone, calcification zone, and ossification zone,
from epiphysis to metaphysis. The process of linear growth initiates at the
epiphyseal end of growth plate and new bone is laid down at the metaphysis,
resulting in new bone formation at the metaphyseal end of the long bone
(Fig. 5.8).5 Rickets–Osteomalacia