Vitamin D toxicity sequalae consists of nonspecific symptoms such as weakness, poor appetite, nausea, emesis, anorexia, weight loss, and polyuria. Due the vagueness of these symptoms, diagnosis is usually delayed until the picture is severe. In chronic toxicity, observed symptoms are abdominal cramps, constipation, polydipsia and backaches. 

Hypercalcemia can lead to serious manifestations such as calcification of cardiac, vascular, and renal tissues [5]. Elevated calcium levels can also cause cardiac arrhythmias. Furthermore, the Women’s Health Initiative demonstrated a 17% increased risk in developing nephrolithiasis in postmenopausal women who ingested of both calcium and vitamin D [6].

Nephrotoxicity

The increased calcium concentration overwhelms glomerular filtration and reduces the rate. Therefore, the excess calcium accumulates in the renal tubules. This phenomenon is observed in about 25% of individuals with vitamin D intoxication. In addition, 10% of nephrocalcinosis in children is due to vitamin D intoxication. The combination of dehydration, reduced filtration and calcium accumulation contributes to renal tubular acidosis. 

Correlation of vitamin D dose, calcium concentration and presentation

The Endocrine Society defines serum calcium concentrations above than 150 ng/mL as toxic. Also, it proposes that the safe levels are less than 100 ng/mL for children and adults. These numbers are supported by studies.

It is not clear what levels of vitamin D lead to toxicity and hypercalcemia. Documented vitamin D intoxication in the pediatric population involves severely elevated levels greater than 240,000 IU. The serum calcium levels in these patients are in the range of 14 to 18 mg/dL. These cases demonstrate that there is variability between the intake of vitamin D and corresponding serum calcium levels. In conclusion, it is difficult to establish what levels are associated with symptomatology.

• Anorexia

  Although the toxicity of vitamin D has conventionally been attributed to its induction of hypercalcemia, animal studies show that the toxic endpoints observed in response to hypervitaminosis D such as anorexia, lethargy, growth retardation, bone resorption [ncbi.nlm.nih.gov]

  Clinical signs: Clinical signs include anorexia, teeth grinding, and weight loss. [dora.missouri.edu]

  Gastrointestinal Symptoms There are certain gastrointestinal symptoms of the toxicity of vitamin D that might include anorexia, vomiting and nausea. [findhomeremedy.com]

  The woman was taking 50,000 IU vitamin D daily and 3,000 mg calcium at least once daily for 3 months, according to researchers, and presented with stage 3 chronic kidney disease and symptoms of severe hypercalcemia, including fatigue, anorexia, weight [healio.com]

• Fever

  Parenteral administration of vitamin D 3 10–14 days before the predicted calving date is considered an effective strategy to prevent periparturient hypocalcemia (milk fever) in dairy cows. [merckvetmanual.com]

  There was no history of fever, headache, cough, urinary symptoms or any focal weakness. She was hypertensive for last 20 years, which was well under control with Amlodipine (5 mg/day). [ncbi.nlm.nih.gov]

  The mother denied that the child had fever, diarrhea, or seizure-like activity. [pediatrics.aappublications.org]

• Malaise

  Other symptoms can be quite nonspecific: Scaly seborrhoeic eczema Patchy hair loss Stomatitis Loss of appetite Nausea Vomiting Malaise Hepatosplenomegaly Liver failure Raised intracranial pressure Children can present with craniotabes, irritability, failure [patient.info]

• Vomiting

  “This led to vitamin D toxicity and the boy was admitted in AIIMS with abdominal pain and vomiting. [timesofindia.indiatimes.com]

  The condition can cause weakness, vomiting and kidney problems, and is the main side effect of high vitamin D levels. [livescience.com]

  Clinical manifestations included nausea, vomiting, altered sensorium, constipation, pancreatitis, acute kidney injury and weight loss. Median (range) age was 64·5 (42-86) years. [ncbi.nlm.nih.gov]

  Signs of vitamin D toxicity can include nausea, vomiting, lack of appetite, constipation, weakness, weight loss or any combination of these. If vitamin D levels get extremely high, it can do your body serious harm. [sharecare.com]

• Nausea

  Clinical manifestations included nausea, vomiting, altered sensorium, constipation, pancreatitis, acute kidney injury and weight loss. Median (range) age was 64·5 (42-86) years. [ncbi.nlm.nih.gov]

  Signs of vitamin D toxicity can include nausea, vomiting, lack of appetite, constipation, weakness, weight loss or any combination of these. If vitamin D levels get extremely high, it can do your body serious harm. [sharecare.com]

  The first symptoms of vitamin D toxicity are loss of appetite, nausea and vomiting, followed by an incredible thirst, increased urination, weakness, anxiety and high blood pressure. [healthfame.com]

  The man experienced some nausea and elevated calcium that improved as soon as he stopped the supplement, with no long-term adverse effect. A health guru taking his own Ultimate Power Meal became sick with nausea and constipation. [dummies.com]

• Constipation

  Constipation Constipation is a condition where bowel movement is painful and hard to pass. [searchhomeremedy.com]

  Constipation Constipation is considered to be one of the major symptoms of vitamin d toxicity because the body is not able to get the desired amount of vitamin D that is considered to be essential for the body and at the same time it is also found that [findhomeremedy.com]

  Clinical manifestations included nausea, vomiting, altered sensorium, constipation, pancreatitis, acute kidney injury and weight loss. Median (range) age was 64·5 (42-86) years. [ncbi.nlm.nih.gov]

  Signs of vitamin D toxicity can include nausea, vomiting, lack of appetite, constipation, weakness, weight loss or any combination of these. If vitamin D levels get extremely high, it can do your body serious harm. [sharecare.com]

  A health guru taking his own Ultimate Power Meal became sick with nausea and constipation. He found that the manufacturer of his meals had been erroneously putting 2 million IU in each meal. [dummies.com]

• Loss of Appetite

  While the physical signs that can arise include nausea, vomiting, loss of appetite, and weight loss. In addition, increased thirst and dehydration, as well as severe headaches can occur. [healthfame.com]

  When symptoms do appear, they may include confusion, increased urination, increased thirst, loss of appetite, vomiting, and muscle weakness. [schmidtlaw.com]

  Dr Sarah Brewer, GP and Medical Director at Healthspan said: “Excess vitamin D leads to raised levels of calcium which can cause headache, loss of appetite, nausea, vomiting, diarrhoea or constipation, palpitations and fatigue.” [express.co.uk]

  However, excessive vitamin D can cause nausea and vomiting, loss of appetite, excessive thirst, frequent urination, constipation, abdominal pain, muscle weakness, muscle and joint aches, confusion, and fatigue, as well as more serious consequences like [fda.gov]

• Polydipsia

  These are the conditions that are followed by polydipsia and polyuria which are conditions of excessive thirst and urine experienced by the body. [findhomeremedy.com]

  There is high blood pressure, anorexia, polyuria, polydipsia, nervousness and itching. Excess vitamin D causes many kidney problems like high protein levels that are excreted in the urine. [searchhomeremedy.com]

  Symptoms of vitamin D toxicity[ 2 ] Hypercalcemia Hypercalciuria Kidney stones Hyperphosphatemia Polyuria Polydipsia Ectopic calcification of soft tissues (kidney and lung) Nausea/vomiting Anorexia Constipation Headache Hypertension Diagnosis of vitamin [ncbi.nlm.nih.gov]

  In chronic toxicity, observed symptoms are abdominal cramps, constipation, polydipsia and backaches. Hypercalcemia can lead to serious manifestations such as calcification of cardiac, vascular, and renal tissues. [symptoma.com]

  Vitamin D overdose causes elevated blood calcium level (hypercalcemia) and the main symptoms are: anorexia, nausea, and vomiting, frequently followed by excessive urination (polyuria), Â increase thirst (polydipsia), weakness, nervousness, itchiness, [drgeo.com]

• Hypertension

  It is suggested that normal renal function may be required for the hypertension of hyperparathyroidism to be reversible and that the hypertension may be directly related to the hypercalcemia in some patients. [ncbi.nlm.nih.gov]

  The patient's hypercalcemia persisted for 14 days and was complicated by persistent hypertension. No renal, cardiac, or neurologic complications were noted. [pediatrics.aappublications.org]

  Low vitamin D levels are associated with all kinds of health problems, including cardiovascular disease, hypertension, type 2 diabetes, multiple sclerosis, cognitive impairment, and even cancer. [doctorshealthpress.com]

  Features of hypercalcaemia include polyuria, polydypsia, vomiting, anorexia, lethargy, dehydration, constipation, hypertension, tetany and seizures. The traditional description of hypercalcaemia is stones, bones and groans. [patient.info]

• Pruritus

  Scaly seborrhoeic eczema Patchy hair loss Stomatitis Loss of appetite Nausea Vomiting Malaise Hepatosplenomegaly Liver failure Raised intracranial pressure Children can present with craniotabes, irritability, failure to thrive, decreased appetite and pruritus [patient.info]

  Anorexia, nausea, and vomiting can develop, often followed by polyuria, polydipsia, weakness, nervousness, pruritus, and eventually renal failure. [merckmanuals.com]

• Bone Pain

  Bone Pain Excessive bone pain is one of the most important symptoms that can be associated with vitamin D toxicity. [findhomeremedy.com]

  Symptoms might progress to bone pain and kidney problems, such as the formation of calcium stones. Treatment includes stopping vitamin D intake and restricting dietary calcium. [mayoclinic.org]

  Bone Pain Excessive calcium as a consequence of higher levels of Vitamin D causes calcification of bones. [searchhomeremedy.com]

• Muscle Weakness

  It's also associated with a wide range of symptoms, including vomiting, constipation, dehydration, fatigue, and muscle weakness. [bostonglobe.com]

  When symptoms do appear, they may include confusion, increased urination, increased thirst, loss of appetite, vomiting, and muscle weakness. [schmidtlaw.com]

  However, excessive vitamin D can cause nausea and vomiting, loss of appetite, excessive thirst, frequent urination, constipation, abdominal pain, muscle weakness, muscle and joint aches, confusion, and fatigue, as well as more serious consequences like [fda.gov]

  Though most often treatable, MedLine Plus identifies constipation, muscle weakness and vomiting as symptoms of vitamin D toxicity. In more severe cases, it can cause damage to the bones and kidneys. [healthyeating.sfgate.com]

• Osteopenia

  Our website has a good article that may be helpful: //www.everydayhealth.com/osteoporosis/guide/osteopenia/ With any new drug, be aware that interaction between medications can occur. [everydayhealth.com]

• Anxiety Disorder

  Effexor XR (venlafaxine ER) is a medication that is used to treat depression and anxiety disorders. [everydayhealth.com]

• Polyuria

  Ten cases of hypercalcemia due to vitamin D intoxication are presented with features of vomiting, polyuria, polydipsia, encephalopathy and renal dysfunction. [ncbi.nlm.nih.gov]

  These are the conditions that are followed by polydipsia and polyuria which are conditions of excessive thirst and urine experienced by the body. [findhomeremedy.com]

  Hypervitaminosis D Vitamin D toxicity can cause nonspecific symptoms such as anorexia, weight loss, polyuria, and heart arrhythmias. [patient.info]

  Hypertension, loss of appetite and weight loss Hypercalcuric symptoms, such as polyuria and renal calculi Long-term toxicity, including increases in mortality from all causes, increased risk of pancreatic cancer, cardiovascular events and falls leading [news-medical.net]

  There is high blood pressure, anorexia, polyuria, polydipsia, nervousness and itching. Excess vitamin D causes many kidney problems like high protein levels that are excreted in the urine. [searchhomeremedy.com]

• Kidney Failure

  Patients with liver disease or chronic kidney failure may be especially vulnerable. [schmidtlaw.com]

  Excessive thirst, an altered level of consciousness, high blood pressure, calcification in the kidney tubes, kidney failure or hearing loss may also develop ( 4, 27 ). [authoritynutrition.com]

• Renal Insufficiency

  insufficiency) can cause secondary hyperPTH to transform into tertiary hyperPTH; the parathyroid glands have been working so hard and long that they start to take a life of their own and continue to pump out PTH without regards for feedback mechanisms [forums.studentdoctor.net]

• Headache

  I've experienced dizziness, headaches, insomnia, heart disturbances (palpitations, sensation of hard beating, mild chest pain), irritated eyes, and generally feeling a bit weird and spaced out. [paleohacks.com]

  There was no history of fever, headache, cough, urinary symptoms or any focal weakness. She was hypertensive for last 20 years, which was well under control with Amlodipine (5 mg/day). [ncbi.nlm.nih.gov]

  More sustained intake of excess vitamin A leads to increased intracranial pressure (pseudotumour cerebri), dizziness, nausea, headaches, skin irritation, pain in joints and bones, coma, and even death. [patient.info]

  Dr Sarah Brewer, GP and Medical Director at Healthspan said: “Excess vitamin D leads to raised levels of calcium which can cause headache, loss of appetite, nausea, vomiting, diarrhoea or constipation, palpitations and fatigue.” [express.co.uk]

  In addition, increased thirst and dehydration, as well as severe headaches can occur. Along with the development of symptoms, nerves and muscles begin to be affected, which causes itching in the skin, fatigue, and weakness. [healthfame.com]

• Lethargy

  Although the toxicity of vitamin D has conventionally been attributed to its induction of hypercalcemia, animal studies show that the toxic endpoints observed in response to hypervitaminosis D such as anorexia, lethargy, growth retardation, bone resorption [ncbi.nlm.nih.gov]

  Features of hypercalcaemia include polyuria, polydypsia, vomiting, anorexia, lethargy, dehydration, constipation, hypertension, tetany and seizures. The traditional description of hypercalcaemia is stones, bones and groans. [patient.info]

  A 67-year-old woman went to the hospital with a history of lethargy, memory impairment, confusion, loss of appetite, and loss of equilibrium for two-weeks duration. Her routine biochemistry showed elevated blood calcium at 14 mg/dl. [secondopinionnewsletter.com]

  This class of drugs gradually reduces Coenzyme Q10 by at least 40% over a period of a year creating such unwanted symptoms such as: fatigue weak and tired muscles lethargy a general sense of low energy A deficiency of coenzyme Q10 can result in high blood [naturallysavvy.com]

• Forgetful

  The woman was admitted to the hospital after she experienced fatigue, forgetfulness, nausea, vomiting, slurred speech and other symptoms ( 9 ). [healthline.com]

  In fact, there can be issues like fatigue and forgetfulness linked to the toxicity problems. Your doctor will be able to check for this by testing your blood levels. There will be signs of poisonous effects right away. [positivehealthwellness.com]

When suspecting ingestion of unknown substance, a thorough history and physical are obtained from the patient or family (if patient is young or unable to speak).

Laboratory tests include electrolytes studies especially in patients with emesis or diarrhea. Calcium concentrations must be obtained (>11mg/dL is considered abnormal). A concomitant elevation in phosphate may occur. Renal functions tests are essential. Additional laboratory studies include urinalysis, which can provide insight regarding renal impairment. Of note, if the following laboratory studies are performed, the observed measurements are as follows:

• Serum 25OHD increased 
• Serum 1,25(OH)2D normal
• PTH reduced

These trends differ in other pathologies with hypercalcemia. 

Imaging consists of a skeletal X-ray to survey all the bones for calcification (especially in vitamin D and A toxicity) [7]. Also important is a hand X-ray, which identifies periosteal calcification in toxicity. An electrocardiogram (EKG) is performed to discover any potential arrhythmias secondary to excess calcium.

• Nephrolithiasis

  Mutations in the CYP24A1 gene cause reduced serum 24,25(OH)2D3 to 25(OH)D3 ratio (<0.02), elevated serum 1,25-dihydroxyvitamin D (1,25(OH)2D3), hypercalcemia, hypercalciuria and nephrolithiasis. [ncbi.nlm.nih.gov]

  Furthermore, the Women’s Health Initiative demonstrated a 17% increased risk in developing nephrolithiasis in postmenopausal women who ingested of both calcium and vitamin D. [symptoma.com]

  Complications Complications may include nephrolithiasis, nephrocalcinosis (calcium oxalate and calcium phosphate are radio-opaque stones), calcinosis of the joints and periarticular tissues, and chronic kidney disease. [patient.info]

• Soft Tissue Calcification

  Since vitamin K is essential to the nervous system and plays important roles in protecting against bone loss and calcification of the peripheral soft tissues, its deficiency results in the symptoms associated with hypervitaminosis D. [ncbi.nlm.nih.gov]

  At best, they will not protect against soft tissue calcification, and at worst, they could perhaps actively faciliate soft tissue calcification. [blog.cholesterol-and-health.com]

  Lesions are consistent with soft-tissue calcification described under enzootic calcinosis (see Lesions ). [merckvetmanual.com]

  tissue calcification, including nephrocalcinosis and kidney stones. 1, 5 The risk of vitamin D toxicity may be increased in individuals who have 5 : granulomatous disorders such as sarcoidosis and tuberculosis some lymphomas that produce 1,25-dihydroxyvitamin [questdiagnostics.com]

• Alkaline Phosphatase Decreased

  Serum phosphate usually decreases, and serum alkaline phosphatase usually increases. Serum PTH may be normal or elevated. [merckmanuals.com]

Symptomatic patients with hypercalcemia should be treated. These are the following interventions:

1. ABCs: In life threatening cases, secure airway and ensure all the necessary precautions. Monitor vitals and provide oxygen as needed. Also evaluate arrhythmias if present. Treatment may be indicated for certain types.
2. Address the source: Expect the levels to reduce gradually over a few weeks. Even after discontinuing the source, 25(OH)D may still increase since due its long half life. Asymptomatic patients with high 25(OH)D concentration should be monitored for development of symptoms [8] [9].
3. IV hydration: Administer normal saline at 1.5 to 2.5 maintenance rate. The goal of this therapy is to improve the glomerular filtration rate and the subsequent excretion of calcium. 
4. Loop diuretics such as furosemide may be helpful. Avoid thiazide since can worsen calcium levels. 
5. Diet: Order low calcium meals. Calcium disodium can use used facilitate fecal excretion. 
6. Other drugs/therapy: Consider steroids, hydrocortisone, and/or mithramycin. In cases of with very high levels of serum calcium, dialysis may be beneficial.
7. Calcitonin and its analogues can be considered as well. If hypercalcemia is secondary to diuretics, calcitonin should be considered. 
8. In cases where patients consume other substances in toxic levels, gastric lavage may be indicated. If iron was ingested as well, this should be treated.

Of note, calcium itself is used therapeutically in conditions such as hyperparathyroidism, psoriasis and other disorders as well.

Patients with vitamin D toxicity have excellent prognosis [1] once they stop intake of the supplements. This also true for toxicity with other vitamins as well. Long term outcomes and fatalities are very rare. This is corroborated by the data published by The American Association of Poison Control Center. Approximately 59,000 single exposures to vitamins were reported in 2012, but there was one fatal case [3] [4].

Vitamin D toxicity is secondary to ingestion of high amounts of dietary vitamin D supplements. Foods rich in calcium do not provide toxic levels of the vitamin. Excessive sun exposure is not a cause of toxicity either, since heat on the skin degrades vitamin D3 and previtamin D3 as they are produced [1]. 

Historically, vitamin D fortification of foods and beverages in the United States and Europe resulted in toxicity [2]. 

The use of supplements is quite prevalent. In fact, a 2009 survey reported that approximately 56% American consumers take vitamin supplements, in which a majority admit to daily consumption. In addition, a study that took place from 2003 to 2006 demonstrated that a third of the United States population had taken a vitamin supplement in any given month.

The United States poison control receives greater than 60,000 reports yearly of vitamin overdoses. The American Association of Poison Control Center documents the relevant data for exposures, adverse outcomes, and mortality rates that stem from overdose [3]. The 2012 statistics for Vitamin D toxcity are:

• Single exposures: 4494
• Minor outcomes: 137
• Moderate outcomes: 19
• Major outcomes or fatal cases: none

To understand the pathophysiology of vitamin D toxicity, it is important to demonstrate the normal physiology. Vitamin D (a prohormone) is metabolized by the liver to 25(OH)D which is then converted to 1,25(OH) 2D by the kidneys. Both metabolites may behave as hormones. The three factors that regulate this conversion are concentration of 1,25(OH) 2D, parathyroid hormone (PTH) and serum levels of calcium and phosphate.

There are three mechanisms responsible for vitamin D toxicity:

1. Vitamin D intake raises serum 1α,25(OH)2D levels and this further elevates cellular levels of 1α,25(OH)2D. Investigations have not demonstrated this mechanism in human or animal studies.
2. Vitamin D ingestion increases serum 25(OH)D which overwhelms the capacity of binding proteins and hence the unbound or "free" 25(OH)D enters the cells and stimulates gene expression. 
3. Vitamin D consumption increases levels of its metabolites especially 25(OH)D. The elevated concentrations of vitamin D and its metabolites overwhelm the binding capacity of the binding proteins. This results in the subsequent release of 1α,25(OH)2D, which enters the cells and stimulates gene expression.

In all three theories, vitamin D metabolites reach the cell nuclei and alter gene expression. Normally, 1α,25(OH)2D3 has a low affinity for the binding protein but has high affinity for vitamin D receptor. In fact, 1α,25(OH)2D3, which is thought to mimic steroids, is the only ligand that can access transcription machinery. With severe levels of vitamin D (such as in intoxication), the other metabolites exceed the number of binding proteins and thus are free to subsequently access the nucleus. Hence, the second and third mechanisms above may be plausible. 

Intoxication with vitamin D is not a frequent occurrence in individuals that use supplements. Those with underlying hepatic or renal disorders are more at risk and should discuss with their doctor before initiating supplement intake. The same recommendation applies to those taking thiazide diuretics. Furthermore, it is pertinent to exercise caution with excessive or chronic intake of vitamins in children. To avoid accidental overdose, parents and caretakers should place all medications and supplements out of the reach of children. In case of suspected ingestion, parents should seek immediate medical attention. 

The recommended daily intake for vitamin D [10] depends on the age:

• 0 to 12 months: 10 mcg or 400 IU
• 1 to 70 years of age: 15 mcg or 600 IU, This also applies to pregnant and lactating women.
• Greater than 70 years of age: 20 mcg or 800 IU

Following nutritional guidelines is recommended for all vitamin and nutrients. 

Vitamin D plays an essential role in the body especially in bone development and mineralization. The fat soluble vitamin facilitates absorption of calcium and phosphate. Physiologically, humans are equipped to handle the synthesis and production of vitamin D (with sunlight exposure) but this does not cause toxicity. The latter occurs from excessive intake such as with supplements.

Toxicity is classified as either acute or chronic. The chronic form is associated with a dose greater than 50,000 IU daily in adults but the acute dose has yet to be clarified. In very young infants, 1000 IU daily is likely unsafe. There are recommendations for dietary intake of this and all vitamins. 

The nonspecific symptoms of toxicity are usually related to hypercalcemia. The vagueness of the clinical picture often delays the diagnosis. Furthermore, there are serious complications such as nephrotoxicity, which is a consequence of calcium accumulation in the renal tubules. 

The therapy consists discontinuation of the source. Treatment depends on the severity of the presentation. Overall, patients recover well. 

Vitamin D toxicity is not a common condition, but when it occurs, it is due to excessive intake of vitamin D such as with supplements. Large amounts of this vitamin cause an increase of calcium in the blood. Symptoms include nausea, vomiting, constipation, poor appetite, frequent urination, tiredness, weakness, and aches. Some patients will have an abnormal heart rhythm. The high calcium levels can cause kidney damage due to build up of calcium in the tubules. 

If your doctor suspects vitamin D toxicity, s/he will order important laboratory blood tests to assess the amount of calcium and phosphate. Also the doctor will order blood and urine tests to evaluate the kidney function. Also, X-rays of the bones may be necessary to detect any bone calcification. 

Treatments of toxicity include hydration with intravenous fluids to facilitate clearing of the excess calcium from the kidneys. Some patients may benefit from loop diuretics, steroids or bisphonates. 

There are recommendations for preventing vitamin D overdose. Patients with liver or kidney disease should ask their doctor before taking any supplement. Also, parents and caretakers should keep all medications and supplements away from children for safety. If there is suspected overdose, seek medical attention immediately.

The following are the recommended daily allowance of vitamin D for 3 main age groups:

• 0 to 12 months: 10 mcg or 400 IU
• 1 to 70 years of age: 15 mcg or 600 IU
• Greater than 70 years of age: 20 mcg or 800 IU

1. Holick MF. Vitamin D deficiency.New England Journal of Medicine. 2007;357(3):266-81.
2. Holick M.F. Vitamin D deficiency: What a pain it is. Mayo Clinic Proceedings. 2003;78(12):1457–1459. 
3. Mowry JB, Spyker DA, Cantilena LR Jr, Bailey JE, Ford M. 2012 Annual Report of the American Association of Poison Control Centers' National Poison Data System (NPDS): 30th Annual Report. Clinical Toxicology (Phila). 2013; 51(10):949-1229.
4. Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database System Review. 2012;14:3.
5. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
6. Jackson RD, LaCroix AZ, Gass M, Wallace RB, Robbins J, Lewis CE, et al. Calcium plus vitamin D supplementation and the risk of fractures. New England Journal of Medicine. 2006;354(7): 669-83.
7. Barker ME, Blumsohn A. Is vitamin A consumption a risk factor for osteoporotic fracture? Proceedings of the Nutrition Society. 2003; 62(4):845-50.
8. Doneray H, Ozkan B, Caner I, Ozkan A, Karakelleoglu C. Intragastric alendronate therapy in two infants with vitamin D intoxication: a new method. Clinical Toxicology (Phila). 2008; 46(4):300–302.
9. Orbak Z, Doneray H, Keskin F, Turgut A, Alp H, Karakelleoglu C. Vitamin D intoxication and therapy with alendronate (case report and review of literature). European Journal of Pediatrics. 2006; 165(8):583–584. 
10. Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D. National Institutes of Health. Available at http://ods.od.nih.gov/factsheets/vitamina.asp. Accessed: October 13, 2014.