Accessibility Notice

What Are Fat-Soluble Vitamins?

For all the body’s intricate biomechanics, the substances of which it is composed fall into two basic categories: fat-soluble, known in biological terms as hydrophobic, and water-soluble, hydrophilic.

“It’s like Italian dressing; if you let it sit, the oil and vinegar don’t mix. Those different sets of physical properties correspond to different chemistries,” says Gerald Combs, Jr., PhD, of the Human Nutrition Research Centre on Aging at Tufts University.

There are good reasons for some vitamins—A, D, E and K—to be soluble in fat. The fatty parts of each cell need protection against harmful molecules called free radicals; fat-based vitamins, by acting as antioxidants*, help provide such protection.*

In addition, “your brain is made of fat. In order to get a nutrient into the brain it helps if the nutrient is fat-soluble,” says Pamela Wartian Smith, MD, MPH, author of What You Must Know About Vitamins, Minerals, Herbs & More (SquareOne).

While eating a varied diet provides vitamins, fat-soluble and otherwise, it may still not be enough to provide optimal levels.

“People always ask me whether or not they need a multivitamin. Because of what we face in today’s world—poor diet, medication usage, pervasive electronics—I would say they do,” says Smith.

Fat-soluble vitamins should be taken with fatty foods. Combs says the body breaks fat down into micelles, microscopic spheres that carry these vitamins into the bloodstream. “If you have poor pancreatic or liver function, that’s going to interfere with micelle formation,” he notes.

A: Supporting Sight and Skin

Vitamin A first came to scientific attention as the substance that helps prevent night blindness, an inability to see after dark*. But subsequent research has found this vitamin to play numerous roles in maintaining health, including support for the immune system and the skin*.

The type of vitamin A used by the body, known as retinol, is found in animal foods such as liver, milk and eggs. In addition, the body can create vitamin A from beta-carotene, a nutrient found in vegetables and fruits. Some people carry a genetic variation that prevents them from converting beta-carotene in retinol and supplementing with retinol in these cases becomes important.

In the UK, poor diet is a primary factor in low A levels. “People don’t eat enough yellow vegetables,” says Smith. Carrots are the well-known source of beta-carotene; others include sweet potatoes, squashes and pumpkin in addition to leafy greens.

D: All-Around Protection

For years, vitamin D was known as the nutrient that helped prevent rickets, a bone-softening disorder most often seen in children*. And while scientists now understand that D is crucial for bone and teeth health at all ages, recent studies have shown this nutrient to support almost every system in the body, including the immune system*.

Combs says, “We find vitamin D receptors in every type of tissue, so this is a leading edge of research.”

Vitamin D is found in eggs, oily fish and milk. However, the most important source is sunlight: the ultraviolet (UV) rays trigger D production in exposed skin. That means the climate you live in helps determine how much vitamin D your body produces. “In temperate latitudes D levels drop in the winter and go up in summer,” says Combs.

Indoor living leads to suboptimal D levels. Window glass filters UV and fluorescent lights produce minimal amounts. As a result, the National Institutes of Health says, “In some groups, dietary supplements might be required to meet the daily need for vitamin D.”

Many researchers would extend that recommendation to much of the population, given the prevalence of low vitamin D levels.

Darker complexions are genetically designed to screen the body from strong and prolonged sun exposure and consequently less vitamin D3 is produced within the skin. People with darker complexions who live in northern latitudes very often supplement to meet their needs.

Vitamin D is available as D2 and D3. “Studies show that supplementing with D3 is better,” says Smith.

E: Crucial Antioxidant

The term “vitamin E” is actually used to describe eight separate substances in two families: the tocopherols, the best-known of which is alpha-tocopherol, and the tocotrienols.

Vitamin E helps support free-radical defense, particularly in the fat-rich parts of cells*.

Food sources of vitamin E include sunflower seeds, nuts and vegetable oils. When taken supplementally, natural E works better than its synthetic counterpart.

K: Bone Aid

Vitamin K got its name from Koagulation, after European researchers discovered it was needed for blood to clot, or coagulate.

As with other vitamins, K comes in different forms. K1 is manufactured by plants while K2 is formed by intestinal bacteria in animals and people. The K2 form, specifically a variant known as MK-4, supports bone health*.

Vitamin K2 and vitamin D3 work synergistically to maintain bone tissue in good health.

* Vitamin E contributes to the protection of cells from oxidative stress

Vitamin A contributes to the maintenance of normal vision, normal skin, normal immune system, normal mucosal membranes, and normal iron metabolism.

Vitamin D contributes to the normal functioning if the immune system, maintenance of muscle function and normal bones and teeth. It also helps to reduce the loss of bone mineral in postmenopausal women, Low bone mineral density is a risk factor for osteoporotic bone fractures.

Vitamin K contributes to the maintenance of normal bones and normal clotting.

The information provided is not an endorsement of any product, and is intended for educational purposes only. NaturesPlus does not provide medical advice and does not offer diagnosis of any conditions. Current research on this topic is not conclusive and further research may be needed in order to prove the benefits described.

The conditions and symptoms described may be indicative of serious health problems, and therefore should be brought to the attention of a qualified healthcare practitioner.

**These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

related articles icon