Most vitamins are described as either fat-soluble or water-soluble. The simple mnemonic
"ADEK" is used to identify the fat-soluble vitamins: vitamins A, D, E and K. Fat-soluble vitamins are stored by the body, in our stores of fat and in our livers, whereas a larger proportion of the water-soluble vitamins we consume pass through our bodies and are excreted in urine.

Any vitamins can be toxic if taken in massively large doses, but the fat-soluble vitamins need to be taken more carefully because of their penchant for building up in our systems. Fat-soluble vitamins are less likely to need to be taken in supplemental form because the body stores them. Also, unlike the water-soluble vitamins, the fat-soluble vitamins do not lose their vitamin content in cooking and preparation.

We are all familiar with the term "RDA"-recommended daily allowance-that is used for vitamins and is found on many vitamin labels and food packages. However, you should also look for the "UL"-upper intake level-to make sure you do not take too much of your vitamins, especially the ones that are fat-soluble.

The description of different vitamins as fat-soluble or water-soluble doesn't refer to the form they come in. It doesn't mean that one kind of vitamins dissolves in water and one doesn't. The terms refer to the way our bodies handle the vitamins. Fat-soluble vitamins are absorbed through our stomachs and intestines and are stored in the liver, while water-soluble vitamins dissolve and are absorbed for immediate use. People are less likely to be deficient in fat-soluble vitamins because our bodies store them, but certain conditions and medications can cause deficiencies in any vitamin. When in doubt, consult your doctor.

Many people take vitamins because of their supposed anti-aging properties, but it's a fact that you need to supplement your vitamins as you get older. The anti-oxidant properties of Vitamins C and E are documented and help to counteract cell deterioration.

Vitamin B12 is one of the vitamins that many older people can be lacking. B12 is one of the vitamins that our body produces by chemical actions inside our stomachs. Some people don't absorb B12 properly and need to get their vitamins supplemented. Over the age of 50, up to 30 percent of the population will have some problem with B12 absorption. Sometimes taking B12 vitamins by mouth can help. However, if the problem is that the stomach cannot absorb B12 vitamins, it may be necessary to get B12 shots, which introduces the vitamins directly into the bloodstream. Your doctor can do blood tests to check your B12 levels.

As we get older, our ability to produce vitamin D also declines. While sun exposure alone is enough to trigger adequate production of D vitamins in most people, by the time we reach age 70 our skin only produces one-quarter the D vitamins it did from the same amount of sun exposure when we were 25. Seniors who are housebound, who live in the northern parts of North America, or who cannot go outside without sunscreen are likely to need to get their D vitamins from supplements.

Certain medications can also interfere with the body's ability to use the vitamins we normally get from food. Be honest with your doctor about your diet and lifestyle and ask what supplementary vitamins you should be taking.