Side Effects of Vitamin D Overdose

The term 'vitamins' refers to a group of organic compounds that are essential for healthy functioning of our body. There are 13 universally recognized vitamins that are broadly classified into water-soluble and fat-soluble vitamins.

Vitamin D refers to a group of fat-soluble vitamins, and the two major forms that are important for human beings are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3).

These are collectively referred to as calciferols. Ergosterol, which is produced by certain plants, fungi, and invertebrates, gets converted to Vitamin D2 by exposure to ultraviolet rays of the sun.

 Cholecalciferol is a prohormone or the precursor to the biologically-active form called 1,25-dihydroxycholecalciferol that is produced by our body in response to exposure to sun.

The dietary sources of vitamin D include fish, eggs, cod liver oil, cheese, and fortified milk.

Though the sunshine vitamin is required in small amounts, it is important to maintain proper levels of vitamin D in the body. A deficiency could lead to rickets and osteomalacia in children and adults respectively.

Since, vitamin D is fat-soluble, taking large doses could have an adverse effect on a person's health. Vitamin D supplements must therefore be taken as per the prescribed dosage.

Side Effects Associated with a Vitamin D Overdose

The importance of taking vitamin D supplements as per the prescribed dosage cannot be stressed enough. Side effects are likely to occur if the supplements are taken beyond the tolerable upper limit.

Here are some of the adverse effects associated with an overdose.

➞ Since vitamin D plays a vital role in the absorption of calcium and phosphorus, taking it in large doses can cause absorption of large amounts of calcium. This could lead to elevated levels of calcium in blood, which in turn, may cause calcification of the heart and kidneys.

➞ High levels of vitamin D may also have a negative effect on the functioning of the renal system. This could be manifested in the form of polyuria, nocturia , polydipsia, or renal failure.

➞ Another side effect of vitamin D overdose is the formation of kidney stones due to calcification of the soft tissues.

➞ Vomiting, weakness of the muscles, fatigue, constipation, dehydration, and irritability are also associated with high levels of vitamin D in the blood.

➞ In addition to the aforementioned side effects, an overdose of vitamin D could also lead to vascular calcification, which in turn, could put a person at an increased risk of developing hypertension and heart diseases.

High doses of vitamin D are contraindicated for those who have elevated blood calcium levels. Those who are taking drugs that help the body absorb calcium (Diltiazem, Verapamil, Thiazide diuretics, etc.) must refrain from taking large doses of vitamin D.

Those who have a vitamin D deficiency may be asked to take a high initial loading dose. After taking the initial loading dose, the patients must take maintenance doses as per the doctor's advice.

Taking initial loading doses for a prolonged period of time can also make a person susceptible to hypercalcemia. Pregnant women must not take vitamin D supplements that contain vitamin A, as that could cause harm to the fetus.

In 2010, the Food and Nutrition Board at the Institute of Medicine (IOM) of the United States National Academies, updated the recommended dietary intake (RDA).

The revised RDA that has been established by the FNB is given as per the age groups.

Daily RDA for Vitamin D

Group - Age - RDA (I.U.)

• Infants - 0-12 months - 400
• Children - 1 year and above - 600

• Adults:

• Less than 70 years - 600
• 70 years and above - 800

The Institute of Medicine also updated the upper tolerable intake level. Here are the tolerable upper intake levels as per the age groups.

Tolerable Upper Intake for Vitamin D

Group - Age - RDA (I.U.)

• Infants:

a.) 0-6 months - 1,000
b.) 6-12 months - 1,500

• Children

a.) 1-3 years - 2,500
b.) 4-8 years - 3,000
c.) 9 years and above - 4,000

Adults - N.A - 4,000

Since vitamin D performs many vital functions, do include the food items that are rich in vitamin D or foods fortified with this vitamin in your diet. Supplementation of vitamin D is usually recommended when a person is affected by a vitamin D deficiency.

Unlike water-soluble vitamins that can be flushed out with urine, fat-soluble vitamins such as vitamin D get stored in the body. Taking these supplements as per the prescribed dosage is the best way to avoid the side effects that are associated with a vitamin D overdose.

Disclaimer: The information provided in this story is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.