Vitamin D toxicity, or hypervitaminosis D is the toxic state of an excess of vitamin D. The normal range for blood concentration is 20 to 50 nanograms per milliliter (ng/mL). However, the toxic state is known to be a value of 100 ng/ml or more in a clinical setting. Signs and symptoms An excess of vitamin D causes abnormally high blood concentrations of calcium, which can cause overcalcification of the bones, soft tissues, heart and kidneys. In addition, hypertension can result. Symptoms of vitamin D toxicity may include the following: Dehydration Vomiting Diarrhea Decreased appetite Irritability Constipation Fatigue Muscle weakness Metastatic calcification of the soft tissues Insomnia Symptoms of vitamin D toxicity appear several months after excessive doses of vitamin D are administered. In almost every case, a low-calcium diet combined with corticosteroid drugs will allow for a full recovery within a month. It is possible that some of the symptoms of vitamin D toxicity are actually due to vitamin K depletion. One animal experiment has demonstrated that co-consumption with vitamin K reduced adverse effects, but this has not been tested in humans. However the interconnected relationships between vitamin A, vitamin D, and vitamin K, outlined in a 2007 paper published in the journal Medical Hypotheses, describes potential feedback loops between these three vitamins that could be elucidated by future research. A mutation of the CYP24A1 gene can lead to a reduction in the degradation of vitamin D and to hypercalcaemia (see Vitamin_D: Excess). Recommended supplement limits The U.S National Academy of Medicine has established a Tolerable Upper Intake Level (UL) to protect against vitamin D toxicity ("The UL is not intended as a target intake; rather, the risk for harm begins to increase once intakes surpass this level."). These levels in microgram (mcg or µg) and International Units (IU) for both males and females, by age, are: (Conversion : 1 µg = 40 IU and 0.025 µg = 1 IU.) 0–6 months: 25 µg/d (1000 IU/d) 7–12 months: 38 µg/d (1500 IU/d) 1–3 years: 63 µg/d (2500 IU/d) 4–8 years:75 µg/d (3000 IU/d) 9+ years:100 µg/d (4000 IU/d) Pregnant and Lactating: 100 µg/d (4000 IU/d) The recommended dietary allowance is 15 µg/d (600 IU per day; 800 IU for those over 70 years). Overdose has been observed at 1,925 µg/d (77,000 IU per day). Acute overdose requires between 15,000 µg/d (600,000 IU per day) and 42,000 µg/d (1,680,000 IU