What to Know About Fat-Soluble Vitamins, According to Experts

These types of vitamins are “stored in the liver and fatty tissue for long-term use,” says Vocca. These vitamins are essential for your body to properly function. Some common fat-soluble vitamins include vitamins A, D, E, and K. These play various roles in the body and support a host of functions, including the immune system, explains Qianzhi Jiang, Ph.D., R.D.N., a pediatric and family dietitian and CEO of The Nutrition Changer.

The concern with the type of vitamin lies within the way it is processed by the body. If you take too much, your body doesn’t get rid of it right away. Instead, “levels can remain high for weeks to months, even if intake stops,” Vocca notes. This is where taking one of these vitamins without a true deficiency may go wrong.

They absolutely can be, when taken under the direction of a healthcare provider and/or dietitian. “Supplementing with fat-soluble vitamins is appropriate when a diagnosed deficiency exists, or with certain medical conditions, such as celiac disease, cystic fibrosis, or pancreatitis,” explains Vocca. It may also be beneficial for those on restrictive diets or during specific life stages, such as during pregnancy or breastfeeding, she adds.

Always consult your physician before adding a vitamin or supplement to your routine. They can run the proper tests to see if you have a deficiency.

Toxicity—the point at which the body is storing too much of a fat-soluble vitamin—is more likely to happen from taking too many vitamins than from getting nutrition from food alone, Vocca notes. “If levels become too high, they don’t drop quickly. It can take weeks to months for the body to normalize,” she adds.

Symptoms of toxicity vary greatly in type and severity, but Vocca says they may include:

• Severe nausea

• Vomiting

• Dizziness

• Joint pain

• Kidney damage

• In severe cases, liver damage, coma, or death

Toxicity is most likely to happen with vitamins A and E, according to our experts. Vitamin A toxicity, specifically, is referred to as hypervitaminosis. “Vitamin A and E share an absorption and transport pathway. Large amounts of one can shift the body’s demand for the other,” Vocca explains. In other words, too much of one or the other may throw off their intertwined process and cause issues.

For instance, children who accidentally ingest their parents’ vitamin A supplements may experience acute toxicity. Long-term intake of too much vitamin A, especially exceeding 8000 retinol activity equivalents (RAEs), may cause toxicity, Jiang adds. Side effects of hypervitaminosis, specifically, include dry skin, hair loss, fatigue, loss of appetite, nausea, vomiting, hypercalcemia (high calcium), impaired bone health, and liver damage.

Symptoms of vitamin E toxicity may not be noticeable until daily intake goes over 1,000 milligrams, Jiang notes. Research has found an increased mortality rate among those who take high doses of vitamin E supplements alone or with other antioxidants.

It’s also worth noting that some fat-soluble vitamins may interfere with medications. “For example, vitamin K can decrease the effectiveness of anticoagulants (blood thinners),” says Vocca. “Fat-soluble vitamins don’t operate in isolation; they influence each other and balance matters just as much as intake.”

While those prescribed fat-soluble vitamins should absolutely follow their physician’s recommendations, be mindful of the amount you’re getting. “Taking these vitamins in supplement form can do more harm than good because the body cannot eliminate them quickly, and their ability to be stored and build up in the body makes them more likely to cause serious side effects,” says Vocca. That’s why “food-first approaches are safest,” Vocca notes, and why it’s important to eat a well-balanced diet. “Nutrients from whole foods are generally safer and more effective,” she adds.

If you believe you could have a fat-soluble vitamin deficiency, “always talk to a healthcare professional before starting any supplements,” Jian concludes.

Dietary supplements are products intended to supplement the diet. They are not medicines and are not intended to treat, diagnose, mitigate, prevent, or cure diseases. Be cautious about taking dietary supplements if you are pregnant or nursing. Also, be careful about giving supplements to a child, unless recommended by their healthcare provider.