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Serum vitamin B 12 is a medical laboratory test that measure vitamin B 12 only in the blood binding to both transcobalamins. [1] Most of the time, 80–94% of vitamin B 12 in the blood binds to haptocorrin, while only 6–20% is binds to transcobalamin ll. [2] Only transcobalamin ll is "active" and can be used by the body. [1]
AI and UL are defined by EFSA the same as in the United States. For women and men over age 18, the adequate intake (AI) is set at 4.0 μg/day. AI for pregnancy is 4.5 μg/day, and for lactation 5.0 μg/day. For children aged 1–14 years, the AIs increase with age from 1.5 to 3.5 μg/day.
References range may vary with age, sex, race, pregnancy, [10] diet, use of prescribed or herbal drugs and stress. Reference ranges often depend on the analytical method used, for reasons such as inaccuracy, lack of standardisation, lack of certified reference material and differing antibody reactivity. [11]
Hypervitaminosis is a condition of abnormally high storage levels of vitamins, which can lead to various symptoms as over excitement, irritability, or even toxicity. Specific medical names of the different conditions are derived from the given vitamin involved: an excess of vitamin A , for example, is called hypervitaminosis A .
Evidence exists linking elevated homocysteine levels with vascular dementia [10] and Alzheimer's disease. [11] [12] [13] There is also evidence that elevated homocysteine levels and low levels of vitamin B6 and B12 are risk factors for mild cognitive impairment and dementia. [14]
Over time, a deficiency of B12 can cause problems with balance, confusion, depression, poor memory and possibly dementia, and it can even cause permanent damage to the nervous system, Somers says.
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Diagnosis is not always straightforward as serum levels can be falsely high or normal. [10] Elevated methylmalonic acid levels may also indicate a deficiency. [2] Individuals with low or marginal values of vitamin B 12 in the range of 148–221 pmol/L (200–300 pg/mL) may not have classic neurological or hematological signs or symptoms. [2]