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Whether you have high vitamin D levels, low vitamin D levels, normal vitamin D levels, or you suffer vitamin D toxicity levels, the only way to know for sure is by taking a simple blood test. Testing for the right kind of vitamin D, however, is essential for finding your true vitamin status.
When it comes to taking vitamin D levels, it's important to know which form of vitamin D needs to be measured. Our bodies store vitamin D as a chemical called 25 (OH) vitamin D. Our bodies transform a tiny fraction of the stored vitamin D, about 0.1% every 2 to 3 hours, to an active form of the vitamin called 1,25 (OH)2 vitamin D. (You can always look up the names, but it is important to know that there are two different forms of the vitamin.) And for the vitamin D level to have any meaning, it's also important to measure a substance called parathyroid hormone. This hormone transforms the storage form of vitamin D into the active form of vitamin D.
Doctors have a better idea of the vitamin D levels associated with deficiency than of the vitamin D levels associated with good health. There is general agreement that if your 25 (OH) vitamin D level is 10 ng/ml (which is equivalent to 25 nmol/L, it's important to look at the units), then you are at immediate risk for losing minerals from bone. This condition is called rickets in children and osteomalacia in adults.
If your 25 (OH) vitamin D levels are 30 ng/ml (75 nmol/L) or higher, there's good agreement that you have all the vitamin D that your body needs for good health. If you have some number in between 10 and 30 ng/ml, however, you may still benefit from taking a supplement.
Normal 1,25 (OH) 2 vitamin D levels run between 12 and 55 pg/ml. This is the activated form of vitamin D. And normal parathyroid hormone levels run between 12 and 50 pg/ml. These are not the first two levels your doctor should be looking for. Usually the level of the storage form of vitamin D is what you are looking for.
We are conditioned to think about vitamins in terms of deficiency. If you don't have enough vitamin D, you will have problems with bones and teeth, immunity, and chronic pain. Fortunately, it's easy to correct vitamin D deficiency. Just take up to 5,000 IU of supplemental vitamin D on a regular basis (or more as your doctor directs).
There is such a thing as too much vitamin D. Too much vitamin D can cause calcium to flow out of your bones and into your bloodstream. This condition, called hypercalcemia, can trigger loss of appetite, nausea, increased urination, and bone pain. (Too little vitamin D causes muscle pain.) Extremely high vitamin D levels are associated with kidney failure. But if you have extremely high D levels, you probably have overdosed on supplemental vitamin D.
When doctors who understand vitamin D look at the numbers, they may notice that:
It is important to remember that there are times you don't need to take vitamin D, you need another kind of treatment. When your stored vitamin D levels are low, however, vitamin D supplements are always recommended.
Ford, Loretta; Graham, Valerie; Wall, Alan; Berg, Jonathan (2006). Vitamin D concentrations in an UK inner-city multicultural outpatient population. Annals of Clinical Biochemistry (The Royal Society of Medicine Press Ltd) 43 (6):
Signorello, LB; Williams, SM; Zheng, W; Smith, JR; Long, J; Cai, Q; Hargreaves, MK; Hollis, BW et al. (2010). Blood vitamin d levels in relation to genetic estimation of African ancestry.Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology 19 (9): 2325–31.