Multiple sclerosis is less common among people living at high altitude, where UV exposure is greater. Patients with multiple sclerosis have poor vitamin D status and low bone density, although this could be a result of the disease rather than a cause. Calcitriol prevents the development of experimental autoimmune encephalomyelitis in mice, a widely accepted model of multiple sclerosis, and it has been suggested that vitamin D supplements may protect genetically susceptible people from developing the disease (Hayes et al., 1997; Hayes, 2000).
A number of studies have shown that there is a north-south gradient in the incidence of type I diabetes mellitus and that children who are given vitamin
D supplements are less at risk of developing the disease. It is not known how vitamin D protects against the development of diabetes, but it may be by modulation of the differentiation of lymphocytes involved in the autoimmune destruction of pancreatic f-islet cells. The protective dose is above current reference intakes and indeed may be above the tolerable upper intake of 25 ^g per day for infants (Harris, 2002).
The calcitriol molecule shows considerable conformational flexibility, and different conformations are required for binding to the plasma vitamin D binding protein (Section 3.2.7), nuclear receptors (Section 3.3.1), and cell surface receptors (Section 3.3.2; Norman et al., 1996; 2001a; 2001b). Because of the roles of vitamin D in regulating cell proliferation and differentiation (Section 3.3.6), there is considerable interest in the development of analogs of calcitriol that have little or no hypercalcemic action, for the treatment of psoriasis and some cancers. Such compounds include calcipotriol (1a,27-dihydroxycholecalciferol), 19-nor-calcidiol, doxercalciferol, 22-oxacalcitriol, and alfacacidiol (Brown, 1998, 2001; Guyton et al., 2001).
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References cited in the text are listed in the Bibliography.
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Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...