What is vitamin D toxicity?
Although rare, build-up of vitamin D in the body due to excessive intake leads to vitamin D toxicity. Since it is almost impossible to get too much vitamin D from sunlight or food, vitamin D toxicity usually results from indiscrete intake of supplements.
Vitamin D supplements are extremely beneficial for the body. This article aims to serve as a guide to taking the correct dose of vitamin D supplements.
Guidelines for optimal blood vitamin D levels
Vitamin D is easily available to people who live in places with abundant sunlight. However, this may not be enough to fulfill daily requirements. Vitamin D is an essential vitamin with a receptor in almost every cell in the body. Dietary sources of vitamin D is mostly restricted to fatty fish. This brings in the necessity of vitamin D supplements.
What are the guidelines for vitamin D dosage?
- 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.
For optimal blood levels, a daily dosage of 1000-4000 IU is sufficient.
Vitamin D daily requirements and upper safety limit
It is difficult to determine the upper safety limit for vitamin D intake since vitamin D toxicity is still less understood. Vitamin D toxicity mostly occurs due to overdose of vitamin D supplements.
A daily intake between 40,000-100,000 IU for a minimum period of one month has been shown to cause vitamin D toxicity.The Institute of Medicine recommends 4000 IU as the upper daily safety limit for vitamin D intake. Yet, in some healthy individuals even 10,000 IU has been shown to not cause toxicity.
It is important to note that several of the reported cases of vitamin D toxicity is due to manufacturing errors by supplement companies. This means that the actual dosage exceeds that printed on the label by 100-4000 times. Blood vitamin D levels resulting from such errors have been reported to be between 257-620 ng/ml.
Vitamin D toxicity can usually be reversed when the normal blood vitamin D levels are restored. However, severe cases may lead to kidney failure and calcification of the arteries.
What are the symptoms of vitamin D toxicity?
Main symptoms of vitamin D toxicity:
- Excessive thirst
- Altered level of consciuosness
- High blood pressure
- Kidney failure
- Hearing loss
Hypercalcemia is the main end result of vitamin D (a.k.a cholecalciferol) toxicity. Hypercalcemia refers to the build up of calcium in the blood. It results in nausea, vomiting, diarrhea, constipation, and weakness.
How is vitamin D toxicity treated?
Treating vitamin D toxicity involves cutting down on all dietary sources of vitamin D. Hypercalcemia may be corrected by administering an intravenous saline to increase salt and fluid in the blood.
Does a large dose of vitamin D always lead to toxicity?
Large doses of vitamin D may not lead to toxicity, yet can still be harmful. These effects are often difficult to detect and complex in nature. There have been cases of individuals who have been taking very high doses of vitamin D without any apparent symptoms. However, blood tests showed severe hypercalcemia and signs of kidney failure.
To avoid vitamin D toxicity, it is advisable to stick to the upper daily safety limit of 4000 IU per day.
Vitamin D and other fat soluble vitamins
Two other fat-soluble vitamins are thought to strongly influence vitamin D toxicity: vitamin K and vitamin A. Vitamin K controls where calcium is deposited in the body. Large amounts of vitamin D may drain the body’s vitamin K stores. Vitamin A, another fat soluble vitamin is known to spare vitamin K stores for the body.Hence taking vitamin A and vitamin K along with magnesium, another important nutrient, may help to reduce chances of calcification of other tissues. However these are just theories. It is recommended to consult a physician or dietitian before going on to take very large doses of vitamin D.
Since vitamin D toxicity is less reported and not well-studied, it is difficult to determine the exact safety dosage limit. As a general rule, it is safe to be within the 4000 IU per day limit. Large doses of vitamin D has not shown to provide any additional benefits, hence it may be unnecessary and even dangerous given the side effects like kidney failure and hypercalcemia.