Causes and Risks of Vitamin D Overdose

Reviewed by: Terri Forehand RN
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Although vitamin D is essential for health, a vitamin D overdose can threaten your health. It causes Hypervitaminosis D, a potentially serious condition that results from toxic levels of this vitamin in the body. As with any supplement, consultation with a physician before self treatment is critical.

Causes of Vitamin D Overdose

The body's daily requirement for vitamin D is relatively low. It naturally produces its daily supply from exposure to sunlight, the primary source of vitamin D. As little as 10 to 15 minutes of sunshine, at least three times a week, is enough to manufacture your body's vitamin D requirement.

This natural production process is safe and will not result in an overdose, because once the body's requirements have been met, further production of this vitamin is shutdown. High dietary intakes of vitamin D from food sources have also been proven to contain concentrations of vitamin D that are too low to cause an overdose (with the exception of cod liver oil).

The most likely cause of a vitamin D overdose is from an excessive intake of supplements. The body does not have a mechanism to shutdown the absorption of large amounts of vitamin D from supplemental vitamin preparations. As such, it builds up to toxic levels, causing Hypervitaminosis D. Such incidents are most closely associated with prescription supplements of vitamin D.

People most vulnerable to an overdose are often those who suffer from rickets or some other disease or condition that is caused by vitamin D deficiency. In this case, pharmacological doses are prescribed for therapeutic purposes. It is critical to discuss this type of prescription with your doctor to ensure you are avoiding toxicity.

What Is the Recommended Dosage?

The U.S. Institute of Medicine of the National Academy of Sciences has established the recommendations for daily intake of vitamin D. No matter what your age, the daily dosage is 5 micrograms (200 IU) per day. However, when using supplements it is possible to double or triple this amount quickly. Therefore, it is advised not to take vitamin D supplements without the specific guidance of your doctor.

How Much Is Too Much?

Vitamin D overdose typically happens over a period of time rather than from a single large dose. This is because, unlike most other essential nutrients we consume, the body does not excrete excess vitamin D. Instead, it is stored in the body's fat cells where it can accumulate to toxic levels over time. Due to this, there is a daily maximum any person can take on a regular, daily basis known as the Upper Intake Level. According to the National Institutes of Health, the Upper Intake Levels (ULs) for vitamin D are as follows:

  • Birth to 12 months of age: 25 micrograms (1,000 IU) a day
  • One year of age or older: 50 micrograms (2,000 IU) a day

Studies have also shown that, taken over long periods of time, consumption of vitamin D in amounts above these amounts above (the ULs) will result in toxicity. The amount of time it takes for this toxicity to develop will vary depending on the amount taken daily and the age of the patient. For example, children under the age of 12 months with a sustained intake of 1,000 micrograms (40,000 IU) a day will produce toxicity in just one to four months. For adults, 2,500 micrograms (100,000 IU) a day may result in toxicity in a few months.

Health Risks of Overdosing on Vitamin D

Some of the health risks of excessive intake of vitamin D include:

  • Elevated levels of calcium in the blood, resulting from an increase in the absorption of calcium in the intestinal tract
  • Abnormally large deposition of amounts of phosphate and calcium in soft tissue such as the lungs, heart and kidneys. These deposits can cause irreversible organ malfunction.
  • Nausea, vomiting, poor appetite and loss of weight
  • High blood pressure, heart rhythm irregularities and increased risk of heart disease
  • Kidney stones and renal failure
  • Excessive production of urine
  • An overdose of Vitamin D in pregnant women can cause mental or physical retardation in babies.
  • Other symptoms include:
    • Bone pain and even bone loss
    • Muscular weakness and fatigue
    • Nervousness and irritability
    • Excessive thirst, dehydration
    • Severe headache
    • Deafness
    • Itchy skin

It is highly recommended that you consult with your doctor or other licensed healthcare professional before you begin to take vitamin D supplements. You should closely follow your doctor's instructions regarding the proper vitamin D dose. A calcium supplement may be necessary if your calcium intake is insufficient. If you notice that you are suffering from symptoms of an overdose of vitamin D, consult with your doctor as soon as possible. You will need to stop taking the vitamin D supplements, and restrict your intake of calcium. Like most good things in life, too much vitamin D can be harmful.

Causes and Risks of Vitamin D Overdose