A Nontoxic Case of Vitamin D Toxicity

Hypervitaminosis D without toxicity

Vitamin D deficiency is highly prevalent and there are an increasing number of reports of vitamin D toxicity, mostly related to the misuse of over-the-counter supplements. We report a case with marked hypervitaminosis D (25(OH)D 196 ng/mL) without clinical or biochemical toxicity and normal serum calcium, phosphorus, and 1,25(OH)2D levels. The decline and normalization of the patient's 25(OH)D and urine calcium after cessation of supplements indicated that these supplements were the likely etiology of her hypervitaminosis D. Over-the-counter medications would benefit from regulation by the Food and Drug Administration to prevent incidental toxicity, as seen in our patient.

Hypovitaminosis D: Is It Time to Consider the Use of Calcifediol?

Hypovitaminosis D is becoming a notable health problem worldwide. A consensus exists among several different medical societies as to the need for adequate levels of vitamin D for bone and general health. The correct method by which to restore normal vitamin D levels is still a matter of debate. Although cholecalciferol remains the most commonly distributed form of vitamin D supplementation worldwide, several drugs with vitamin D activity are available for clinical use, and making the correct selection for the individual patient may be challenging. In this narrative review, we aim to contribute to the current knowledge base on the possible and appropriate use of calcifediol-the 25-alpha-hydroxylated metabolite-in relation to its chemical characteristics, its biological properties, and its pathophysiological aspects. Furthermore, we examine the trials that have aimed to evaluate the effect of calcifediol on the restoration of normal vitamin D levels. Calcifediol is more soluble than cholecalciferol in organic solvents, due to its high polarity. Good intestinal absorption and high affinity for the vitamin-D-binding protein positively affect the bioavailability of calcifediol compared with cholecalciferol. In particular, orally administered calcifediol shows a much shorter half-life than oral cholecalciferol. Most findings suggest that oral calcifediol is about three- to five-fold more powerful than oral cholecalciferol, and that it has a higher rate of intestinal absorption. Accordingly, calcifediol can be particularly useful in treating diseases associated with decreased intestinal absorption, as well as obesity (given its lower trapping in the adipose tissue) and potentially neurological diseases treated with drugs that interfere with the hepatic cytochrome P-450 enzyme system, resulting in decreased synthesis of calcifediol. Up to now, there has not been enough clinical evidence for its use in the context of osteoporosis treatment.

Acute hepatologic and nephrologic effects of calcitriol in Syrian golden hamster (Mesocricetus auratus)

Although vitamin D is included in the group of fat-soluble vitamins, it must be considered as a prohormone. Its active forms, including calcitriol, have pleiotropic effects and play an important role in the regulation of cell proliferation, differentiation and apoptosis, as well as in hormone secretion, and they demonstrate anti-cancer properties. Since calcitriol delivery can be beneficial for the organism, and Syrian golden hamsters represent a unique experimental model, we decided to investigate its toxicity in this species. In this study, we injected calcitriol intraperitoneally at doses 0 (control), 0.180±0.009 µg/kg and 0.717±0.032 µg/kg. Animal behavior was observed for 72 hrs after injection, and afterwards blood, liver and kidneys were collected for post-mortem examination, electron microscopy, and hematology analyses. The highest dose of calcitriol induced a change in animal behavior from calm to aggressive, and the liver surface showed morphological signs of damage. Following injection of calcitriol, ultrastructural changes were also observed in the liver and kidneys, e.g. vacuolization and increased number of mitochondria. There was also a trend for increased serum levels of aspartate aminotransferase (AST), but not of alanine aminotransferase (ALT) or GGTP (gamma-glutamyl transpeptidase). There was no change in Ca, Mg and P levels, as well as in blood morphology between experimental and control groups. These results indicate that calcitriol at 0.717, but not at 0.180 µg/kg, may induce acute damage to the liver and kidneys, without inducing calcemia. We propose that the hepatotoxic effect of calcitriol in hamster constitutes the primary cause of behavioral changes.

Can adverse effects of excessive vitamin D supplementation occur without developing hypervitaminosis D?

Vitamin D is a fat-soluble hormone that has endocrine, paracrine and autocrine functions. Consumption of vitamin D-supplemented food & drugs have increased significantly in the last couple of decades due to campaign and awareness programs. Despite such wide use of artificial vitamin D supplements, serum level of 25 hydroxyvitamin D does not always reflect the amount of uptake. In contrast to the safe sunlight exposure, prolonged and disproportionate consumption of vitamin D supplements may lead to vitamin D intoxication, even without developing hypervitaminosis D. One of the reasons why vitamin D supplementation is believed to be safe is, it rarely raises serum vitamin D levels to the toxic range even after repeated intravenous ingestion of extremely high doses of synthetic vitamin D analogs. However, prolonged consumption of vitamin D supplementation may induce hypercalcemia, hypercalciuria and hyperphosphatemia, which are considered to be the initial signs of vitamin D intoxication. It is likely that calcium and phosphorus dysregulation, induced by exogenous vitamin D supplementation, may lead to tissue and organ damages, even without developing hypervitaminosis D. It is needed to be emphasized that, because of tight homeostatic control of calcium and phosphorus, when hypercalcemia and/or hyperphosphatemia is apparent following vitamin D supplementation, the process of tissue and/or organ damage might already have been started.

Vitamin D metabolism in growing pigs: influence of UVB irradiation and dietary vitamin D supply on calcium homeostasis, its regulation and bone metabolism

The aim of this study was to prove whether pigs are able to synthesize vitamin D (vitD) in the skin and to investigate the influence of ultraviolet irradiation (UVB) on vitD status and calcium (Ca) homeostasis of growing pigs. Thirty-two 11-week-old pigs were kept without access to sunlight and divided into four groups receiving the following treatment in a 2 × 2 factorial design: (i) UVB irradiation or not and (ii) vitD in feed or not. Blood, urine and faeces were sampled every third week. In serum, vitD metabolites, Ca, phosphorus (P), magnesium (Mg) and bone markers were analysed. Digestibility of Ca, P and Mg as well as urinary excretion of these minerals was analysed. After 14 weeks, the animals were slaughtered, and samples of skin, intestines, kidneys and bones (metatarsus) were taken for further analyses: sterols of vitD synthesis in the skin, Ca flux rates in the intestines, expression of genes involved in Ca transport in the intestines and kidneys, bone mineral density (BMD) with the aid of peripheral quantitative computer tomography and bone mineral content by ashing the metatarsus. Irradiated animals showed higher levels of 7-dehydrocholesterol and tachysterol in the skin, higher levels of 25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol in the serum and higher Ca net flux rates were determined in Ussing chambers. In contrast, the expression of genes involved in Ca transport in the intestines and kidneys was not altered. Similarly, the digestibility of Ca and P as well as the urinary excretion was not affected. With respect to the metatarsus, no differences in mineral contents and BMD were found between groups. At the end of the study, some subclinical signs of beginning vitD 'insufficiency' were observed in the group without access to vitD (represented by higher expression of 1α-hydroxylase in the kidney and increased parathyroid hormone in serum).

How much is too much? Two contrasting cases of excessive vitamin D supplementation

BACKGROUND

In this report, we describe 2 contrasting cases of hypervitaminosis D.

CASE PRESENTATION

Patient 1 was a 75-y old man who developed symptomatic hypercalcemia (peak serum calcium concentration of 15.3mg/dl; reference range: 8.5-10.6mg/dl), cardiac injury, and a high total serum vitamin D concentration of 243ng/ml (30-80ng/ml) as a result of daily consumption of prescribed 50,000IU ergocalciferol (vitamin D2) and 500mg calcium-citrate for 1y. Patient 2 was a 60-y old woman who consumed 40,000IU of cholecalciferol (vitamin D3) daily for >10months with a peak total serum vitamin D concentration of 479ng/ml (30-80ng/ml), but did not present with symptoms related to vitamin D toxicity.

CONCLUSION

These cases demonstrate that individual responses to supraphysiologic concentrations of vitamin D for extended periods of time vary widely, and that defining a toxic concentration of this vitamin is difficult. The different outcomes in these two patients, despite months of high-dose vitamin D therapy, demonstrates that individual patient pharmacodynamics determine clinical sequelae.

Prevalence of hypercalcemia related to hypervitaminosis D in clinical practice

BACKGROUND & AIMS

Recent interest in vitamin D has led to a substantial increase in the use of vitamin D supplements. Vitamin D intoxication may be a concern as hypervitaminosis D can result in irreversible calcification of soft tissues so that it is important to detect early markers of vitamin D intoxication. Our aim was to assess the simultaneous presence of biochemical markers of vitamin D toxicity (i.e. hypervitaminosis D, hypercalcemia) and determine the concentrations of 25-OH-vitamin D at which the risk of hypercalcemia, and thus toxicity, might begin.

METHODS

We evaluated retrospectively a 6-year period during which 25.567 samples were assessed for 25-OH-vitamin D status by UHPLC. Hypervitaminosis D was defined at serum 25-OH-vitamin D >160 nmol/L. Serum and urine calcium, phosphorus and iPTH were also recorded, if available. Medical history revision was performed in subjects displaying simultaneously hypervitaminosis D and hypercalcemia.

RESULTS

Overall, hypervitaminosis D was found in 475 samples (1.86%) of which 51 displayed hypercalcemia (11.1%). A total of 382 samples were identified as the first record of hypervitaminosis D and 39 presented hypercalcemia (10.2%), most of them at 25-OH-vitamin D levels between 161 and 375 nmol/L. Only in 15 subjects, hypercalcemia could be directly attributed to vitamin D and serum 25-OH-vitamin D ranged between 164 and 1139 nmol/l. In no case, serum calcium achieved concentrations considered as critical values (>13 mg/dl).

CONCLUSION

Hypercalcemia due to vitamin D represented <4% of the total hypervitaminosis D detected and <0.1% of the tests performed. However, a highly variable response was observed and most subjects presented hypercalcemia at serum concentrations of 25-OH-vitamin D < 375 nmol/L.