Although many vitamins have health benefits, not all patients or dosages will experience these benefits. This article presents a case study of vitamin D toxicity and addresses the benefits and risks of both fat- and water-soluble vitamins.

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The case

Recently, an 89-year-old man in the United Kingdom died of hypercalcemia, and lab reports suggest that vitamin D supplements may be to blame.

Hypercalcemia can cause heart and kidney problems and weaken the bones. Because vitamin D helps the body absorb calcium, taking too much vitamin D can lead to calcium buildup, increasing calcium levels in the blood and putting people at risk of hypercalcemia.

The man had been taking vitamin D supplements for at least nine months before his death, according to the reports. According to Business Insider, a coroner said that the vitamin D supplements were not adequately labelled with the risks of excess use.[1]

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Addressing whether a vitamin can benefit a patient

While many vitamins provide health benefits, these benefits do not apply to every patient or at every dosage. When talking to patients about the risks of vitamin supplementation, it can be a good idea first to address the benefits they are seeking and whether they apply to the individual. 

For instance, supplementing with certain vitamins may be helpful for a vitamin-deficient patient. However, if the patient already has adequate vitamin levels from a healthy diet or other sources, supplementation may not be beneficial.

One example of this is people who supplement with vitamin B12. Vitamin B12 supplementation can be helpful for patients who follow a strict vegetarian or vegan diet, as they may be at risk for vitamin B12 deficiencies. In patients who eat hearty diets of meat and vegetables alike, vitamin B12 deficiencies are less common, and supplementation can be less helpful.[2]

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Risks of water-soluble versus fat-soluble vitamins

Two main categories of vitamins are water-soluble and fat-soluble vitamins, referring to how the vitamin is absorbed or excreted by the body. Water-soluble vitamins are more quickly filtered out by the kidneys. Because the body does not store these vitamins for a long time, people must regularly replenish them through food or supplementation if their diet is lacking. People are also less likely to incur serious side effects from taking too many water-soluble vitamin supplements, as they are removed from the body quickly.[2]

Fat-soluble vitamins, on the other hand, dissolve in fat and are stored in the body for a longer period. These do not need to be replenished as quickly, and taking too many fat-soluble vitamins is more likely to lead to vitamin toxicity or other unwanted side effects.

“Overdosing on vitamins like A, D, E, K, or iron supplements can have serious consequences for your health, including nausea, dizziness, and even organ damage in severe cases,” says Raj Dasgupta, MD, a quadruple board-certified physician specialising in internal medicine, pulmonology, critical care, and sleep medicine, and Chief Medical Advisor for Sleep Advisor. 

Dr Dasgupta encourages doctors to remind patients to consult them before “significantly increasing intake of any vitamin or supplement on [their] own.”

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Risks and benefits of fat-soluble vitamins

It can be important to educate patients on how the body stores fat-soluble vitamins so that they understand why they may or may not need supplementation—and how risks occur.

Fat-soluble vitamins include vitamins A, D, E, and K.

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Vitamin A risks and benefits

Vitamin A is a fat-soluble vitamin that supports bodily mechanisms like white blood cell formation, cell growth, bone health, and eye health. Most people in the United States do not experience vitamin A deficiency and do not need to take a vitamin A supplement; however, exceptions do exist.[2]

People who do not experience vitamin A deficiency and take too much vitamin A may be at risk for vitamin A toxicity, which can produce symptoms like:[2]

• Vision changes
• Bone pain
• Nausea and vomiting
• Dry skin
• Sensitivity to light

An overdose of vitamin A can also impact the liver, Dr. Dasgupta says.

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Vitamin D risks and benefits

Vitamin D is a fat-soluble vitamin that helps the body absorb calcium and phosphorus, supporting bone health. Among vitamin deficiencies, vitamin D deficiencies can be more common than others and can produce symptoms like muscle and bone weakness, fatigue, hair loss or brittle hair, depression, loss of appetite, and pale skin. However, vitamin D toxicity can cause serious issues like hypercalcemia, which can lead to symptoms like:[3]

• Nausea and vomiting
• Weakness
• Frequent urination

“An excess of vitamin D can be harmful to your kidneys. This is why following recommended doses [and] treatment plans, and talking to your doctor before deciding to increase your vitamin or supplement intake, is extremely important.”

-Dr Dasgupta

Since both vitamin D deficiencies and toxicities are concerning, it can be important to check a person's vitamin D levels to guide their treatment.

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Vitamin E risks and benefits 

Vitamin E is a fat-soluble vitamin that helps protect cells. In the US, both vitamin E deficiencies and toxicities are rare and typically do not cause symptoms. When symptoms do occur, they might include:[4]

• Bleeding
• Muscle weakness
• Fatigue
• Nausea
• Diarrhea
• Vitamin K risks and benefits

Vitamin K is a fat-soluble vitamin that supports blood clotting and bone growth. Deficiencies and toxicities are rare but can be severe. It can still be important to talk to patients about vitamin K interactions, especially if they are on blood thinners.

Some blood thinners can block vitamin K, which may require modifications to your patient's vitamin K intake to keep them healthy. This does not always have to do with supplements and could pertain to dietary choices. It can be smart to evaluate cases and medications individually.[5]

Water-soluble vitamins may also pose risks. For example, niacin, or vitamin B3, has been linked to vascular inflammation. In any case, staying on top of risks and benefits and encouraging patients to be cautious and ask questions can help keep you and your patients safe and informed. 

Disclaimer: This story is contributed by Claire Wolters and is a part of our Global Content Initiative, where we feature selected stories from our Global network which we believe would be most useful and informative to our doctor members.