Vitamin D is acquiring an increasingly relevant role in health, not only for its role in our immune system against viruses and bacteria but also for its function in our musculoskeletal metabolism in addition to the calcium homeostasis that we are all familiar with.
The consumption of vitamin D-supplemented foods and medications has increased significantly in the last two decades due to awareness campaigns and programs.
Vitamin D is a fat-soluble hormone that has endocrine, paracrine and autocrine functions. Safe exposure to sunlight, along with diet and vitamin D supplementation are the sources of vitamin D. Vitamin D is added to many fortified foods, including dairy and whole-grain products.
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Effects of vitamin D
The endocrine functions of vitamin D are mainly involved in the regulation of calcium and phosphate metabolism, influencing bone and tooth mineralization.
The paracrine and autocrine effects of vitamin D mainly influence cellular homeostasis by affecting cell proliferation, differentiation and survival and, therefore, its deregulation could in turn contribute to the genesis of pathologies such as cancer and accelerated aging.
In addition to the functions mentioned above, vitamin D also exerts extra-skeletal functions on skeletal muscle, immune regulation, cardiovascular health and metabolic activities.
How vitamin D is synthesized
Sunlight exposure-mediated vitamin D synthesis begins in the skin and continues in the liver and kidneys to produce biologically active 1,25-dihydroxyvitamin D3.
Cutaneous biosynthesis of vitamin D3 is tightly regulated to ensure that overproduction of vitamin D and subsequent toxicity does not occur after exposure to ultraviolet B (UBV) sunlight.
Vitamin D hypervitaminosis
Hypervitaminosis occurs when there is an excessive intake of a vitamin. In the case of vitamin D, it can occur from excessive doses of vitamin D or from very high doses over a prolonged period of time. If you want more scientific information, you can consult this article from the US National Library of Medicine.
The clinical manifestations are varied, but are mainly related to hypercalcemia:
- Symptoms of vitamin D toxicity (VDT) include neuropsychiatric manifestations, such as difficulty concentrating, confusion, apathy, drowsiness, depression, psychosis, and, in extreme cases, stupor and coma.
- Gastrointestinal symptoms of VDT include recurrent vomiting, abdominal pain, polydipsia, anorexia, constipation, peptic ulcers and pancreatitis.
- Cardiovascular manifestations of VDT include hypertension, shortened QT interval, ST-segment elevation, and bradyarrhythmias with first-degree heart block on the electrocardiogram.
- Renal symptoms include hypercalciuria as the earliest sign, polyuria, polydipsia, dehydration, nephrocalcinosis, and renal failure.
How to diagnose if you have vitamin D hypervitaminosis
An early diagnosis of VDT requires a detailed clinical and pharmacologic history. VDT in most patients is the result of excessive doses or too-frequent dosing intervals of vitamin D.
Because of the current popularity of vitamin D as a treatment agent for many diseases, vitamin D supplementation (including the use of therapeutic doses) has become prevalent in healthy individuals.
Laboratory tests, in case of hypervitaminosis, would show intact PTH, 25(OH)D concentration >150 ng/ml (>375 nmol/l), and normal or increased values of 1,25(OH) 2 D concentration.
Therefore, the most sensible thing to do is to supplement vitamin D only under medical prescription because of all the harm it can cause.