Harmful effects of excess Vitamin D

Harmful effects of excess Vitamin D

Apr 01, 2019

Vitamin D3  is one of the essential micronutrients required by our body. It is a fat-soluble vitamin which means that it requires fat to get absorbed into our body. Vitamin D deficiency is prevalent across the globe. Lack of exposure to sunlight, insufficient dietary intake, dairy allergy and vegetarian diets are some of the causative factors which might lead to low levels of vitamin D in our body.

Vitamin D plays a major role in our body. It is required for bone health, adequate absorption of calcium and phosphorus, and healthy heart functioning. Due to the increase in awareness of the crucial role played by vitamin D and its widespread deficiency, people are resorting to vitamin D supplements to meet the adequacy levels. Supplements are a perfect solution to meet our nutritional needs. They give additional support to our diet and help in achieving our dietary needs and fitness goals. Since vitamin D is a fat-soluble vitamin so it should not be present in an excess amount in our body. As it can’t be excreted out of the body through urine leading to toxicity. The normal range for blood concentration of vitamin D is 30-50 ng/mL. In case the levels reach beyond 100 ng/mL, then it results in Hypervitaminosis D.


 Vitamin D and calcium absorption are inter-linked with each other and high levels of vitamin D results in high blood concentration of calcium, termed as Hypercalcemia. This toxicity might result in symptoms like weakness, nausea, vomiting, constipation, diarrhoea, frequent urination and loss of appetite. High blood calcium consequences in over-calcification of bones, kidney and heart. Some individuals also develop hypertension, kidney problems and the formation of calcium stones.

 Hansen K.E. (2011) conducted two random placebo-controlled clinical trials. One group with vitamin D insufficiency was given vitamin D therapy to achieve serum concentration level of 25-hydroxycholecalciferol more than 30 ng/mL. Findings indicated that this group didn’t experience any decrease in bone resorption. Another group having serum levels > 30 ng/mL was given yearly high doses of vitamin D which eventually led to a higher number of falls and fractures. So study outcomes indicated that high levels of vitamin D makes our bones weak and brittle therefore more prone to breakage. It is not necessary that serum 25-hydoxycholecalciferol > 30 ng/mL is optimal for all.

 Let’s understand the mechanism behind high calcium levels and high incidence of fractures and falls. Vitamin D is converted into its activated form for absorption in the kidneys by the action of parathyroid hormone (PTH). This process triggers the absorption of calcium in the intestine from food in case of dietary sufficiency. In case of dietary insufficiency, this mechanism results in the leaching of calcium from bones in order to maintain the serum calcium levels. Excess of vitamin D leads to bone resorption and excess leaching  resulting in weak, brittle and porous bones. Sanders K.M. et al. (2010) conducted placebo-controlled trial on 2256 women. All the subjects were 70 years or older and were administered with a single annual dose of 500,000 IU of cholecalciferol orally. Study findings indicated that women in the cholecalciferol group had serum 25-hydoxycholecalciferol was 49nmol/L which is higher than adequate levels. This group had 171 fractures vs. 135 in the placebo group. 837 women in the vitamin D group fell 2892 times while 769 women in the placebo group fell 2512 times. So it won’t be incorrect to conclude that excess of vitamin D levels is closely associated with hypercalcemia.

 Another interesting case study was presented by Genzen J.R. (2014). A 30-year-old female was admitted in emergency department with a 5-day history of extreme abdominal pain, nausea and vomiting. She had thyroid and had been taking multivitamin supplements of A, B and D, as well as a calcium-rich zeolite supplement. Her clinical tests indicated low sodium and potassium levels but elevated calcium levels. The patient had serum 25-hydoxycholecalciferol level of 409 ng/mL. Further findings and discussion with patient revealed that she had been taking large quantities of vitamin D for an unknown period of time.

 To conclude, always follow the golden rule that excess of anything is bad for the body. Though vitamin D is an essential vitamin and has numerous roles to perform in our body for bone, kidney and heart health but high levels can have adverse effects on our health. The repercussion of high vitamin D levels are associated with high calcium levels which makes our skeletal structure weak and vulnerable to fractures. High serum calcium levels increase the risk of developing kidney calcium stones. Metabolism of vitamin D involves other organs like kidneys and endocrine system, hence hypervitaminosis D will also attack the smooth functioning of these processes. It is suggested to regularly monitor vitamin D level so as to prevent any deficiency or excess. Supplements in the form of vitamin D capsules are consumed to fill the gap between dietary intake and recommended daily allowances. Carefully read the nutritional label and decide the dosages as per your need or as guided by a medical expert. Buy multivitamin


  • Koul, P. A., Ahmad, S. H., Ahmad, F., Jan, R. A., Shah, S. U., & Khan, U. H. (2011). Vitamin d toxicity in adults: a case series from an area with endemic hypovitaminosis d. Oman medical journal, 26(3), 201–204. doi:10.5001/omj.2011.49
  • Hansen K. E. (2011). High-dose vitamin D: helpful or harmful?. Current rheumatology reports, 13(3), 257–264. doi:10.1007/s11926-011-0175-9
  • Alshahrani, F., & Aljohani, N. (2013). Vitamin D: deficiency, sufficiency and toxicity. Nutrients, 5(9), 3605–3616. doi:10.3390/nu5093605
  • Sanders, Kerrie M., Stuart, A. L., Williamson, E. J.(2010).Annual high-dose oral vitamin D and falls and fractures in older women: a randomized controlled trial.JAMA Network.303(18),1815-22
  • Genzen, J.R.(2014).Hypercalcemic Crisis Due to Vitamin D Toxicity.Lab Medicine.45,147-150