While the health benefits of vitamin D, vitamin C, vitamin K, vitamin B12 and vitamin E are well documented, knowing how the body absorbs such nutrients can be helpful. Understanding the dangers of vitamin toxicity and overdose is also important, especially because some vitamins and minerals stay in one's body longer than others.
Most such vitamins are fat soluble, and one's body absorbs them differently than water-soluble nutrients.
Vitamins A, D, E, and K are all fat-soluble and can be found in many everyday plant and animal foods, and in dietary supplements. One of the things that sets fat-soluble vitamins apart is how they are processed and stored in the body.
Fat-soluble vitamins vs. water-soluble vitamins
Where water-soluble vitamins dissolve in water and are mostly eliminated in one's urine, fat-soluble vitamins dissolve in fat and oils and tend to accumulate in one's body –usually absorbed with dietary fats in the small intestine and kept in fatty tissues and the liver. "This affects how the vitamin is absorbed, transported and stored," says Josh Redd, NMD, the founder of RedRiver Health and Wellness and author of "The Truth About Low Thyroid."
Redd explains that the absorption and breakdown of fat-soluble vitamins depends, in part, on healthy bile secretion from one's gallbladder. "If our patients have had their gallbladders removed, we advise them to take an enzyme to help improve the absorption of these vitamins," he says.
What are the functions of fat-soluble vitamins?
Fat-soluble vitamins are nutrients one's body needs to stay healthy and function the way it should. "Some of the most important nutrients for our health are the fat-soluble vitamins A, D, E, and K," says Redd. "Fat-soluble vitamins are vital for brain and immune health and serve as powerful antioxidants and anti-inflammatory compounds."
Such nutrients aid one's immune, muscle and nervous systems, strengthen bones and improve eye and skin health. "Vitamin A contributes to reproductive functions, vitamin D has been shown to strengthen our immune system; vitamin D is essential for bone health. Vitamin E contributes to the prevention of oxidative stress and free radicals, and vitamin K is critical for blood clotting," says Lisa Young, PhD, an adjunct professor of nutrition at New York University and author of "Finally Full, Finally Slim."
Are fat-soluble vitamins good for you?
As a result of such vital functions, "fat-soluble vitamins are essential in the diet and promote growth, reproduction and health," explains Young. What's more, because of the way fat-soluble vitamins are stored and processed, one is less likely to be deficient in them than in water-soluble nutrients. "The advantage of fat-soluble vitamins is that they can build into a reserve for use when dietary intake is low," says Redd.
At the same time, many popular low-fat diets have led to fat-soluble vitamin deficiencies for some people. Symptoms of such deficiencies include bone deformities, bleeding issues, gum disease, a weakened immune system and increased risk of cardiovascular disease.
The downside of fat-soluble vitamins being absorbed and stored longer than water-soluble nutrients is that they are more likely to cause toxicity or overdosing issues. "Because fat-soluble vitamins are stored in the body, a big concern is potential for toxicity," explains Young. Side effects related to the overdosing of fat-soluble vitamins A, D, and E, have been linked to cases of nausea, irregular heartbeat, organ damage, hemorrhages and extremely rare cases of death.
But the experts say the risk of overdosing or of vitamin toxicity are very rare when obtaining the nutrients from plant and animal sources. Such issues are more commonly caused through dietary supplement mega dosing.
In most cases, one can safely derive all the fat-soluble nutrients one's body needs from a healthy diet. "Foods rich in fat-soluble vitamins include animal fats, fatty meats, egg yolks, dairy, fatty fish and fish oils, raw nuts and seeds, and avocado oil," says Redd.
