Excess vitamin d
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Excess Vitamin D: Health Implications and Risks
Introduction to Vitamin D and Its Importance
Vitamin D is essential for various bodily functions, including calcium and phosphorus absorption, bone health, and immune system regulation. It is synthesized in the skin upon exposure to sunlight and can also be obtained from dietary sources and supplements. However, while adequate vitamin D is crucial for health, excessive intake can lead to adverse effects.
Subclinical Health Effects of Excess Vitamin D
A study examining individuals consuming overfortified milk for at least four years found that increased milk consumption was associated with higher serum 25-hydroxyvitamin D (25[OH]D) and urinary calcium levels. Despite this, the prevalence of elevated serum 25(OH)D and calcium was not higher than expected, and renal function remained normal, indicating no measurable adverse subclinical effects in most individuals1.
Dietary Calcium and Vitamin D Toxicity
Research on rats has shown that dietary calcium restriction combined with excess vitamin D3 can impair the responsiveness of renal 1-hydroxylase to parathyroid hormone (PTH) and enhance the metabolic clearance of 1,25-dihydroxyvitamin D3. This suggests that calcium intake plays a significant role in modulating the effects of excess vitamin D2.
Health Risks of Excessive Vitamin D Intake
Excessive vitamin D can lead to soft-tissue calcification, hypercalcemia, and hypercalciuria. In severe cases, it can cause nephrocalcinosis and chronic renal failure. The narrow margin between beneficial and harmful doses of vitamin D necessitates careful monitoring and regulation of vitamin D fortification in foods and supplements3 4 6.
Vitamin D Toxicity in Pediatrics
Although rare, vitamin D toxicity in children can occur, particularly due to manufacturing errors or excessive supplementation. Cases of severe hypercalcemia and nephrocalcinosis have been reported, emphasizing the need for monitoring vitamin D levels in children receiving high doses of supplementation4.
Vitamin D and Athletes
Athletes often consume high doses of vitamin D supplements, but excessive intake can be detrimental. Toxic effects are generally observed when serum 25[OH]D concentrations exceed 180 nmol/L. There is also a paradoxical relationship between serum 25[OH]D concentration, ethnicity, and bone health, suggesting that genetic differences may influence vitamin D metabolism5.
Conclusion
While vitamin D is vital for health, excessive intake poses significant risks, including soft-tissue calcification, hypercalcemia, and renal issues. Careful regulation of vitamin D fortification and supplementation is essential to prevent toxicity, particularly in vulnerable populations such as children and the elderly. Further research is needed to establish safe upper limits and to understand the long-term effects of high-dose vitamin D supplementation.
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Most relevant research papers on this topic
Subclinical health effects in a population exposed to excess vitamin D in milk.
Excess vitamin D in milk does not cause measurable adverse subclinical effects, with most individuals exposed to excess vitamin D showing normal renal function.
Observational StudyThe role of dietary calcium in the physiology of vitamin D toxicity: excess dietary vitamin D3 blunts parathyroid hormone induction of kidney 1-hydroxylase.
Excess vitamin D3 in a low-calcium diet impairs renal 1-OHase responsiveness to PTH and enhances metabolic clearance of 1,25(OH)2D3.
RCT
Animal StudyThe relationship of adequate and excessive intake of vitamin D to health and disease.
Most individuals are at risk of obtaining too much vitamin D, so fortification of foods and excessive fortification of animal foods should be curtailed and dietary supplements restricted to prevent tissue damage.
Vitamin D supplementation and risk of toxicity in pediatrics: a review of current literature.
Vitamin D toxicity in children is rare but life-threatening, and monitoring levels is recommended for infants receiving long-term supplementation at or above the recommended upper intake.
Systematic Review
Rigorous Journal
Highly CitedVitamin D and the Athlete: Current Perspectives and New Challenges
High-dose vitamin D supplementation in athletes may be problematic, and data on ethnicity and vitamin D levels may require re-examination to establish new thresholds and target concentrations.
Rigorous JournalHighly CitedVitamin D and bone health in the elderly.
A daily intake of 15 to 20 micrograms of vitamin D is recommended for the elderly, with higher doses potentially being harmful, especially in patients with sarcoidosis or renal calculi.
Highly CitedExtra-Skeletal Effects of Vitamin D
Vitamin D deficiency may have a limited impact on extra-skeletal conditions, with most randomized controlled trials and meta-analyses failing to confirm a causative link.
Systematic Review
Very Rigorous JournalHighly CitedVitamin D deficiency and mortality
Vitamin D deficiency is linked to excess mortality, but future studies should clarify the extent to which vitamin D supplementation can improve survival in the aging population and specific patient groups.
Systematic ReviewHighly CitedNon-musculoskeletal benefits of vitamin D
Vitamin D has significant non-skeletal benefits, including regulation of blood pressure, cardiovascular protection, and reduced incidence and severity of common cancers, autoimmune diseases, and infectious diseases.
Systematic ReviewHighly CitedVitamin D and chronic pain
Low vitamin D levels may contribute to chronic pain, but the evidence for a link between vitamin D deficiency and chronic pain remains inconclusive.
Systematic ReviewVery Rigorous JournalHighly Cited