Adverse Effects and Harms of Excessive Vitamin D Supplementation

Vitamin D is the only vitamin our body can produce; it is also one of the vitamins that can be stored in the body. Its most important role is bone health through calcium, while its many roles in immune and cellular function are increasingly understood. Deficiency of this vitamin, which has these important roles, may require supplementation in some circumstances. However, excessive supplementation can also cause adverse effects.

How Is Vitamin D Produced in Our Body, Obtained From Food and Stored?

Vitamin D has 2 forms: Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

The first step in vitamin D3 synthesis is sunlight-driven conversion of skin provitamin D into vitamin D3 (cholecalciferol). It then binds vitamin D-binding proteins (DBP) and is transported to target organs.

Absorption of dietary vitamin D from the intestines is another source. D3 is mostly found in animal foods such as oily fish, while D2 occurs in small amounts in plants and mushrooms and is also found in supplements as D2. Dietary vitamin D is transported to the liver by fat molecules called chylomicrons.

Vitamin D reaching the liver undergoes hydroxylation by the enzyme 25-hydroxylase, forming 25-hydroxyvitamin D (25-OHD). In the kidneys, 25-OHD is converted to 1,25-dihydroxyvitamin D (1, 25 OHD). 1,25-OHDis vitamin D's physiologically active formas such.

Vitamin D level is based on measurement of the precursor hormone 25-OHD as the indicator. The most stable and abundant vitamin D metabolite in serum, 25-OHD has a half-life of 3 weeks, making it the most suitable indicator of vitamin D level.

The main tissue storing vitamin D is fat. Some is also stored in muscle tissue.

The Most Serious Adverse Effects of Excess Vitamin D Intake

Vitamin D can be obtained from sunlight, diet or supplements. However, prolonged use of supplements beyond what is needed can cause disorders.

Adverse effects that uncontrolled excessive vitamin D intake may cause include;

• Hypercalcemia (excess calcium)
• Kidney Damage
• Irregular Heartbeat and Heart Attack
• Bone Pain and Tenderness
• Dehydration (Fluid Loss)
• Pancreatitis
• Lung Damage

Hypercalcemia (excess calcium)

Excess vitamin D intake is linked to hypercalcemia (excess calcium), meaning too much calcium in the blood. Vitamin D and calcium are strongly related. High blood vitamin D increases the amount of calcium absorbed in the intestines, potentially accelerating calcium release into the bloodstream. Excess calcium in the blood can then cause various complications (problems) and symptoms (complaints).

Some of the most serious signs of hypercalcemia include:

• Loss of appetite
• Diarrhea and constipation
• Nausea and vomiting
• Joint and muscle pain
• Persistent headache
• Irritability and anxiety
• Muscle weakness
• An irregular heartbeat
• Reduced reflexes
• High blood pressure

Kidney damage

Excess calcium in the bloodstream can bind phosphate, allowing crystals to accumulate in soft tissues. These crystals may cause tissue damage and eventually organ damage.

As a passageway consisting of millions of tiny filters, the kidney is vulnerable to calcium deposits.

When calcium deposits become trapped in kidney tissue, nephrocalcinosis (kidney stones) may occur. If severe, this can cause permanent kidney damage and eventually kidney failure.

Symptoms of nephrocalcinosis (kidney stones) include:

• Nausea and vomiting
• Fever and chills
• Pain in the abdomen, back or groin, including the testicles in men

Irregular heartbeat and heart attack

Extreme hypercalcemia can reduce or alter heart cell function. People with severe hypercalcemia therefore experience heartbeat irregularities.

In someone with high blood calcium or phosphate due to excess vitamin D, calcium may accumulate or form plaques in arteries or heart valves.

Some signs of cardiac complications include:

• An irregular heartbeat that may be temporary or persistent
• Chest pain
• Unexplained exhaustion
• High blood pressure
• Pain during exercise
• Dizziness

Bone pain and tenderness

When excessive calcium circulates freely in the bloodstream, the body may lack sufficient hormones to bind minerals effectively to bone.

Excess vitamin D can cause bone problems.

Some symptoms include: 

• Bone pain
• Sudden falls
• Bones prone to fracture
• Postural problems
• Back or joint pain
• Loss of height

Dehydration (fluid loss)

Very high vitamin D levels can cause dehydration (a lack of body water).

High calcium levels may reduce the effects of antidiuretic hormones that allow the kidneys to retain water.

These hormones encourage the kidneys to retain water and prevent fluid loss. When blood calcium rises, their activity decreases, and the body loses excess fluid while excreting calcium in urine, potentially causing dehydration (fluid loss).

Symptoms of moderate dehydration include:

• Dry mouth
• Feeling restless
• Irritability
• Dry, stinging eyes
• Increased thirst 
• Decreased urine output

Severe dehydration can be life-threatening.

Other signs and symptoms include:

• Low pulse rate
• Unexplained weakness
• Very little or no urination
• Reduced consciousness

Pancreatitis

Hypercalcemia can cause acute pancreatitis, meaning inflammation of the pancreas.

Pancreatitis symptoms include:

• Upper abdominal pain radiating to the back
• Nausea and vomiting
• Rapid pulse
• Weight loss
• Fever

Lung damage

Formation of calcium and phosphate crystals at high blood levels causes deposits in soft tissues.

Crystals are known to accumulate particularly in the lungs.

Some symptoms of the resulting lung damage include:

• Coughing
• Shortness of breath
• Chest pain

How Common Are Adverse Effects From Excess Vitamin D?

Many people take high-dose vitamin D supplements, and adverse effects are relatively uncommon. The body stores vitamin D in fatty tissues, and adverse effects from excess vitamin D can sometimes take weeks or months to appear.

Who Should Avoid Vitamin D Supplements?

Vitamin D supplements are not suitable for everyone. They can interact with certain medications.

People treated with any of the following drugs should consult a doctor before taking vitamin D supplements.

• Steroids
• Phenobarbital and phenytoin, used to treat epilepsy
• Orlistat (a drug used for obesity treatment)
• Cholestyramine, which can lower cholesterol

Certain medical conditions may also increase vitamin D sensitivity.

A person with any of the following conditions should consult a doctor before using vitamin D supplements.

• Primary hyperthyroidism
• Cancer
• Sarcoidosis
• Granulomatous tuberculosis
• Bone metastasis

Conclusion

In conclusion, vitamin D is a vitamin the body can also produce and store in fatty tissue.

Excess vitamin D adverse effects can cause a wide variety of symptoms (complaints) and present differently in each individual.

Adverse effect risk is higher when a person takes vitamin supplements for a long time or in excessive amounts. Vitamin D and its metabolites (products) may accumulate in the blood. We therefore do not recommend vitamin D supplementation unless blood testing demonstrates a deficiency.

You May Be Interested:

• Vitamin D and Cancer! Does Deficiency Cause Cancer? Do High Levels Prevent Cancer?
• What Are the Symptoms and Causes of Vitamin D Deficiency?