The answer is that we all do for good health. And this is where it's useful to know the difference between water-soluble and fat-soluble vitamins.
First of all, let's talk about the water-soluble ones. These are typically found in fruit, vegetables and grains. Unlike fat-soluble vitamins, they can be destroyed by heat or exposure to the air. They can also be lost in water used for cooking, meaning that by cooking foods, especially boiling them, we lose many of the vitamins. The best way to retain as many of the water-soluble vitamins as possible is to steam, grill or stir fry foods.
And now to fat-soluble vitamins. Unlike the water-soluble vitamins that need regular replacement in the body, fat-soluble vitamins are stored in the body for future use. They are stored mainly in the liver and fatty tissues. While it serves us well to build up a store of these vitamins so that they are there when we need them, if we consume more than we need it leads to toxicity.
The body can be deficient in fat-soluble vitamins if fat intake is too low or if fat absorption is compromised, for example, by certain drugs that interfere with the absorption of fat from the intestine, or by certain diseases such as cystic fibrosis.
Fat-soluble vitamins are found mainly in fatty foods such as animal fats, including butter and lard, vegetable oils, dairy foods, liver and oily fish. You might also be interested to know that, unlike water-soluble vitamins, fat soluble vitamins are not destroyed by the cooking process.
Essential to be consumed with food
The best way to take any kind of fat-soluble supplement is with food - your body will not be able to dissolve or absorb the vitamin otherwise. A glass of low-fat milk for example, would provide a sufficient amount of fat to help your body absorb the vitamin.