Just like how Popeye becomes strong after having a can of spinach, do you also imagine yourself like that after popping a multivitamin pill? Since multivitamins promise to include a wealth of vital nutrients in just one pill, they resemble a mystical potion. But remember this before downing a few like candy: even the strongest elixirs can have unexpected effects. If you exceed recommended dosages, it can lead to certain worse-than-desirable adverse effects. 

Here, we will discuss the science behind vitamin toxicity, and look into the perfect balance for effective and safe use of multivitamin supplements.

Understanding the role of vitamins

Before talking about the negative consequences of taking too many multivitamins, it is important to understand the role of vitamins in our bodies. Vitamins are small molecules that nourish the body. These are also essential for proper functioning and growth of the body. Our body is not able to synthesise vitamins itself.

Therefore, to fulfil the body’s needs, vitamins must be consumed through diet. Some natural food items are enriched with vitamins, however, processed foods are fortified with vitamins. Vitamins perform a variety of duties inside our bodies. They regulate metabolism, help maintain mental health, aid in keeping a normal appetite, and prevent the occurrence of chronic diseases such as diseases of the heart and cancer, etc.

Multivitamins: the nutritional boost

Capsules or tablets containing a blend of essential vitamins and minerals are called multivitamins. These preparations are actually supplements with the goal of supplying these micronutrients required by our systems for a variety of processes, on a daily basis.

The purpose of multivitamins is to bridge dietary gaps. For every product, the recommended dietary allowance (RDA) or percent daily value (DV) of the nutrients in a single serving is listed on the label. So, if a label claims that it contains 100% DV of vitamin D, it means that the supplement will supply 100% of the vitamin D which is required by your body. This value of RDA or DV differs according to age and gender.

Why do people take multivitamins?

Vitamins and nutritional supplements are typically consumed to enhance well-being or health. They are not a source of energy. They also require an ample supply of other macronutrients like carbohydrates, fats, proteins, and even some minerals for their proper functioning.

Moreover, they are not always beneficial for everyone. Supplements containing active ingredients have physiologic or pharmacologic effects, just like prescription medications. Yet, they can also exert negative effects on individuals who are susceptible to these active ingredients.¹

A common misconception among people is that taking supplements of vitamins can have additional health benefits if they take them in amounts higher than the RDA. The most widely used over-the-counter vitamin preparations often don't include more than 100% of the recommended daily allowance (RDA).

However, individuals taking supplements containing a single vitamin or supplements together with a balanced diet that includes fortified foods and beverages are more likely to consume excessive amounts of vitamins. This results in a condition known as hypervitaminosis or simply vitamin toxicity.²

Why do vitamins in excess cause toxicity?

There are two types of vitamins: fat-soluble and water-soluble vitamins. What distinguishes the two is their solubility. 

Fat-soluble vitamins

These are soluble in fats and the body stores these vitamins in fatty tissues, such as the liver and adipose tissues. These include Vitamins A, D, E and K. There are two sides to this storage system. It guarantees a continuous supply, but it also makes it more difficult for the body to eliminate excess amounts. Overdosing on fat-soluble vitamins can eventually lead to potentially dangerous concentrations as they tend to accumulate in the body. This might cause issues.³

Water-soluble vitamins 

These vitamins do not significantly accumulate in the body because they are able to dissolve in water. Urine serves as their continuous means of elimination. Although water-soluble vitamins are less likely to cause toxicity, long-term overdosing can still have negative effects. These include vitamins B and C.⁴

What are the potential risks of taking vitamins in excess?

Certain water-soluble vitamins can have undesirable effects when consumed in excess, some of which might be detrimental. Since consuming large amounts of naturally occurring vitamin K does not seem to be risky, there is no upper intake level (UL) for it. Similar to vitamin K, other water-soluble vitamins does not appear to be unsafe. Vitamins B1 (thiamine), B2 (riboflavin), B5 (pantothenic acid), B7 (biotin), and B12 (cobalamin) are among these vitamins.

Listed below are different types of vitamins with possible effects of overconsuming each vitamin than recommended. 

Vitamin A

Acute symptoms of vitamin A toxicity includes:

• Nausea
• Headache
• Blurred vision
• Vomiting
• Dizziness
• Irritability
• Intracranial hypertension

While chronic symptoms of vitamin A toxicity includes:

• Dry and itchy skin
• Fatigue
• Hair loss
• Anorexia
• Bone and joint pain
• Weight loss

Excessive amounts of vitamin A in the body also alters the metabolism of bone and thereby, affecting the structure of bones and joints. If a pregnant person is assigned a female at birth (AFAB) to use it for longer durations, it can also affect the baby.⁵

Vitamin D

Vitamin D toxicity may present itself in the form of symptoms associated with hypercalcemia; a condition characterised by an increased level of calcium in the body.

Symptoms of vitamin D toxicity may include:

• Confusion
• Stupor
• Psychosis
• Coma
• Abdominal pain
• Excessive thirst
• Vomiting
• Anorexia
• Inflammation of pancreas
• Constipation
• Increased blood pressure
• Heart diseases
• Missing parts of teeth enamel^6,7

Vitamin E

The biggest concern with vitamin E toxicity is the risk of bleeding. Excessive levels of vitamin E in the body may also increase the chances of stroke caused by bleeding in the brain. Other side effects include liver dysfunction, bruising and an unhealthy appearance of skin.⁸

Vitamin K 

This vitamin is available in two forms K₁ and K₂, and both are said to be safe for the majority of individuals when consumed by mouth or taken through an injection. There are very few cases of vitamin K intoxication. Blood sugar levels must be monitored if a person has diabetes since vitamin K1 may lower blood sugar levels.

Only type K3 vitamin K toxicity can cause hemolytic anaemia due to the formation of reactive oxygen species (ROS). In hemolytic anaemia, red blood cells are destroyed by the ROS. This also leads to liver damage and jaundice. This is usually seen in newborns and is not common in adults.^9,10

Vitamin C

Symptoms of vitamin C toxicity may include:

Vitamin B 

Toxicity caused by Vitamin B is given in the table below (table 1):^2,11,12

Table 1. The toxicity caused by each type of vitamin B

Summary

Vitamins are necessary for people to be healthy, yet too much (just like too little) of it can be dangerous. It's not like popping vitamins like candy will give you Popeye muscles—in fact, you might get into trouble!

Vitamins A, D, E, and K are soluble in fat and can accumulate in the body, whereas excess vitamins B and C that are soluble in water are removed from the body through urine. The trouble is that those stored fat-soluble vitamins can cause all kinds of problems, depending on the specific vitamin. Comparable to a treasure box, where the riches are the healthy vitamins and their overabundance can cause mayhem. Therefore, it’s crucial to take vitamins as prescribed and to stick to daily recommendations.