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Vitamin D - how to manage low levels

A quick reminder of vitamin D metabolism is useful here: vitamin D is either absorbed in the diet or produced in the skin by photoconversion of 7-dehydrocholesterol. It is converted by the liver to 25(OH)D3, which is the major form of vitamin D circulating in the blood compartment. The kidney converts 25OHD to 1,25OHD and 24,25OHD, and it is these 2 forms which are active. Abidec, Dalavit and vitA&D capsules provide VitD2 (calciferol). Aquadek and Adcal-D3 and colecalciferol from hospital pharmacies are VitD3 (colecalciferol). At annual review We measure total 25-OH vitamin D2 and D3 in the blood (although the standard Vit D assay in many hospitals just measures D3). The CF Trust recommends that total levels of 25OHD are between 75 and 150nmol/L (or 30 and 60ng/ml). Action required depends on the levels of vitamin D and PTH as follows:

Serum 25OH vitamin D level above 75nmol/L and normal PTH:

• no action

PTH high:

• Serum 25OH level 50-75 nmol/L; give 50-60,000iu colecalciferol D3 weekly for 4 weeks (ie 4 doses)
• Serum 25OH level <50 nmol/L; give 50-60,000iu colecalciferol D3 weekly for 6 weeks (ie 6 doses)
• Repeat 25OHD and PTH after 3 months

PTH normal:

• Serum 25OH level 50-75 nmol/L; give one dose of 50-60,000iu colecalciferol D3
• Serum 25OH level 25-50 nmol/L; give 50-60,000iu colecalciferol D3 weekly for 2 weeks (ie 2 doses)
• Serum 25OH level <25 nmol/L; give 50-60,000iu colecalciferol D3 weekly for 4 weeks (ie 4 doses)
• Repeat 25OHD and PTH after 6 months

Then:

• check compliance and modify if necessary. Note the all fat soluble vitamins should be given with fat containing food and creon
• consider increasing dose of routine daily vitamin D (use colecalciferol - there are lots of preparations available now) upto a maximum of 3000iu per day if under 5yrs and 6000iu per day for older children. This is particularly important if the vitamin D is low on repeated testing.
• be careful not to increase vitamin A&D combined preparations such that vitamin A levels exceed the upper limit of normal (1.7 micromol/L < 10 years, 2.9 micromol/L > 10 years). High levels of vitamin A can be detrimental to bone health.
• this usually means that maximum dose of dalavit is around 2.4ml per day and the maximum number of A&D capsules is 4 per day. This provides 1600iu of vitamin D.
• If calcium intake is low, use Calcichew D3 Forte; these chewable tablets contain 12.6mmol calcium (500mg) and 400iu vitamin D.