Can You Take Too Much Vitamin D

Overview

Vitamin D is essential for maintaining a healthy life by regulating calcium levels. The recommended daily vitamin D intake is 400 to 800 international units per day. People often use vitamin supplements to increase their vitamin D levels to maintain this requirement. Taking supplements on their own brings the question, "Can you take too much vitamin D?" We will try to answer these questions and discuss various aspects of vitamin D and its overuse.

Vitamin D deficiency has become a very common condition and has affected immunity, bone mineralization, and overall health. So, vitamin D supplements are prescribed to prevent vitamin D deficiency. Since vitamin D deficiency has become a common condition, many people take vitamin D supplements in the form of tablets, sachets, or injections. These supplements, taken under the prescription and instruction of a doctor, are usually within the recommended safety limit. If your doctor prescribed more than the safety limit, your vitamin D level would be regularly monitored by the prescribing doctor. However, sometimes people take supplements on their own, which increases the risk of vitamin D overdose, especially when it remains unchecked, and too much vitamin D has negative outcomes for your health.

Vitamin D toxicity is known to be caused by an intake of more than 60,000 international units per day for several months. Since such a high level of vitamin D cannot be obtained from diet or sun exposure, toxicity due to increased dietary intake of vitamin D or sun exposure is very rare. It is mostly when people self-prescribe themselves multiple vitamin supplements without consulting their healthcare provider or accidental intake. The toxicity is also called hypervitaminosis or vitamin D intoxication.

This article intends to explain the negative outcome, the symptoms of toxicity, what to do if you have got toxicity, and how not to overdose yourself.

Risk Factors for Vitamin D Toxicity

As we have discussed, vitamin D toxicity is mostly due to an overdose of supplements, but toxicity can be more common in some than in others. Also, overdosage can be an accidental or prescription error. 

Overdose is also seen in patients who take vitamin D replacement therapy for malabsorption, renal osteodystrophy, osteoporosis, or psoriasis. There are also reports suggesting hypervitaminosis may be due to errors in manufacturing, formulation, or prescription, including milk that was excessively fortified with vitamin D.

A few risk factors for developing vitamin D toxicity are mentioned below:

• Granulomatous disorders
• Certain congenital disorders.
• Some lymphomas
• Dysregulated vitamin D metabolism
• Certain medications like thiazide diuretics, digoxin, estrogen therapy, antacids, and isoniazid

Effects of Vitamin D Toxicity

Vitamin D regulates calcium metabolism and increases the calcium level in the blood by increasing calcium absorption from food in the GI tract and calcium resorption from the kidney. So, the signs and symptoms of vitamin D overdose are usually due to increased calcium levels in the blood. Sometimes, hypercalcemia can be life-threatening and needs immediate attention.

Some of the common effects of taking too much vitamin D are explained below: 

• Gastrointestinal symptoms: Gastrointestinal symptoms such as constipation, loss of appetite, nausea, vomiting, and diarrhea are the common symptoms associated with hypercalcemia. However, symptoms and their severity can vary in different individuals. Less commonly, pancreatitis and peptic ulcer disease can also be associated with hypercalcemia.

Gastrointestinal symptoms are more common when the calcium level reaches more than 12mg/dl. Thus, an overdose of vitamin D can lead to gastrointestinal symptoms by increasing the calcium level in the blood.

• Neuropsychiatric abnormalities: Hypercalcemia induced by excess vitamin D can cause psychiatric symptoms such as irritability, nervousness, depression, psychosis, and confusion. The condition can also cause unresponsiveness and can be life-threatening.
  
  
• Kidney problems: Excess calcium in the blood can cause calcium deposition in the kidney, resulting in kidney stones. Additionally, calcium can also cause constriction of blood vessels supplying the kidney and lead to kidney injury. If the condition persists, this may also eventually cause kidney failure.

The most common renal manifestation is polyuria, which is due to a defect in the ability of the kidney to concentrate urine. The combination of polyuria and lack of fluid intake due to nausea can lead to dehydration and further exacerbate hypercalcemia.

• Cardiovascular disease: Hypercalcemia can lead to abnormalities in cardiac conduction, resulting in supraventricular or ventricular arrhythmias.

Longstanding hypercalcemia can cause calcium deposition in heart valves, coronary arteries, and myocardial fibers, resulting in hypertension and cardiomyopathy.

• Musculoskeletal Symptoms: Hypercalcemia can also cause muscle weakness, bone pain, and a reduction in bone mass. A reduction in bone mass can increase the risk of fractures.
  
  

• Other symptoms associated with hypercalcemia are:

  • Increased thirst
  • Increased urination
  • Fatigue and dizziness
  • Weight loss
  • A ringing sensation in the ear

Diagnosis

The doctor would ask you about your symptoms and your medical condition. Your healthcare provider would also review the medicines and supplements that you are taking.

The doctor may also order the following tests:

• Blood tests to check vitamin D levels: Guidelines for blood levels of vitamin D: 
  • Sufficient: 20–30 ng/mL, or 50–75 nmol/L
  • Safe upper limit: 60 ng/mL, or 150 nmol/L
  • Toxic: above 150 ng/mL, or 375 nmol/L
• Blood test to check for calcium and phosphorous levels to determine kidney damage.
• Urine tests to determine if there is excess calcium in the urine
• Radiological investigations like bone X-rays to determine significant bone loss.
• Dysregulated vitamin D metabolism

The liver has the capacity to metabolize vitamin D to an inactive form, and alcohol, barbiturates, and phenytoin enhance this activity. However, this activity is insufficient to treat intoxication due to ingesting large amounts of vitamin D. 

The liver is the usual site of vitamin D storage, but when an excess of vitamin D is ingested, it gets stored in fat, can stay in body fat for a longer period, and is released slowly. This is why hypercalcemia caused by an overdose of vitamin D may take a long time to resolve.

The treatment for the condition is to stop vitamin D supplements completely and limit the diet's calcium content. You might also be advised to limit exposure to the sun and reduce your diet containing vitamin D.

For acute, severe forms of hypercalcemia, intravenous saline fluids are considered. Additionally, calcitonin can be used in combination with fluids and bisphosphonates for immediate and short-term management of hypercalcemia in symptomatic patients.

Bisphonates and corticosteroids are also prescribed for longer-term control of hypercalcemia.

Prevention

The maximum upper limit for the daily vitamin D intake, unlikely to result in any negative consequences, is 4000 IU. This may be lower in infants and children. Adverse effects can be possible in those taking more than 10,000 IU/day but are usually seen in those taking more than 60,000 IU/day of vitamin D over an extended period of time. So, the safety window for the dose of vitamin D is greater. Therefore, it is highly unlikely that dietary intake or sun exposure would lead to an overdose.

However, the toxicity is common, and it is due to the intake of vitamin D in the form of supplements without a prescription or accidental intake. 

So, you can avoid the toxicity by following certain precautions:

• You should consume medicines under the prescription of the doctor.
  
  
• You should try to achieve the recommended daily allowance from your diet. Supplements are only recommended if there is a deficiency or risk factors associated with vitamin D deficiency. Some of the dietary products rich in vitamin D are cod liver oil, fatty fish such as salmon and tuna, beef liver, cheese, egg yolks, and some mushrooms.

Moderate exposure to sunlight for around 15 minutes before applying sunscreen could also be an excellent way to obtain vitamin D naturally.

Final insights

Vitamin D is an essential element in the diet required for various bodily functions, such as immune function, protecting bones and muscles, and maintaining calcium homeostasis.

Although vitamin D can be obtained from a healthy diet and adequate exposure to the sun, there might be a deficiency of vitamin D in specific risk populations, and a vitamin D supplement is necessary in such cases.

If vitamin D deficiency is identified, your healthcare provider might prescribe you a vitamin D supplement at a safer level. However, you might overdose yourself with an excess amount of vitamin D due to certain reasons, like accidental intake, mislabeled products, and not following your doctor's advice. So, the question arises, "Can you take too much vitamin D?" The answer is no.

Suppose you are consuming a high dose of vitamin D supplements or injections. In that case, you might experience symptoms associated with increased calcium levels in the blood, which can also be life-threatening. So, suppose you suspect that you have been consuming vitamin D more than the recommended ( more than 4000 IU/day), or you have symptoms suggestive of hypercalcemia. In that case, you need to consult your doctor.

The doctor might order certain tests to document vitamin D and calcium levels in the blood and plan the appropriate course of treatment.

Sources:

1. DeLuca Hector, F. (2004). Overview of general physiologic features and functions of vitamin D.[J]. The American journal of clinical nutrition, 80(6 Suppl).
2. 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.
3. Mosekilde, L. (2008). Vitamin D requirement and setting recommendation levels: long-term perspectives. Nutrition reviews, 66(suppl_2), S170-S177.
4. Ross, A. C., Manson, J. E., Abrams, S. A., Aloia, J. F., Brannon, P. M., Clinton, S. K., ... & Shapses, S. A. (2011). The 2011 report on dietary reference intakes for calcium and vitamin D from the Institute of Medicine: what clinicians need to know. The Journal of Clinical Endocrinology & Metabolism, 96(1), 53-58.
5. Vieth, R. (2007). Vitamin D toxicity, policy, and science. Journal of Bone and Mineral Research, 22(S2), V64-V68.
6. Jacobus, C. H., Holick, M. F., Shao, Q., Chen, T. C., Holm, I. A., Kolodny, J. M., ... & Seely, E. W. (1992). Hypervitaminosis D associated with drinking milk. New England Journal of Medicine, 326(18), 1173-1177.