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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, known in biological terms as lipid, and water. This split extends to vitamins, which are either fat-soluble or water-soluble.

“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 Center 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, sound eating may 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 preformed A or retinol, is found in such animal foods as liver, milk and eggs. In addition, the body can create vitamin A from beta-carotene, a nutrient found in vegetables and fruits.

In the US, poor diet is a primary factor in low A levels. “People don’t eat enough yellow vegetables,” says Smith. Carrots are the best-known source of beta-carotene; others include sweet potatoes and winter squash 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 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, fatty fish and milk. However, the most important source is sunlight, the ultraviolet (UV) rays of which 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. “Even people who take most multivitamins don’t get enough D,” notes Combs.

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 fatty 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.*

†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.

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