• Health & Wellness

    If You Choose to Take Vitamins as Supplements, Stick to the RDA

If You Choose to Take Vitamins as Supplements, Stick to the RDA

April 22, 2011

Dear Mayo Clinic:

It seems as though recommendations about vitamins change on a weekly basis. Should I be taking vitamin supplements? If so, which ones?


Your body needs vitamins in small amounts. In general, getting those vitamins through the foods you eat is best. But if you choose to take vitamins as supplements, stick as closely as you can to the Recommended Dietary Allowances (RDA).

Within our bodies, all kinds of metabolic processes are going on that involve carbohydrates, fats and proteins. Vitamins serve a vital function by aiding in the chemical reactions that are part of those processes. Our bodies can't produce vitamins, though. To maintain good health, we need to get them in our diet or possibly through vitamin supplements.

The type and amount of vitamins found in food usually aren't the same as those in supplements, however. Food contains vitamins in the concentration and combinations that allow our bodies to use them best. Vitamins in a supplement may not always be in the correct amounts or the ideal form. That said, if you have a deficiency, it's sometimes necessary to take a vitamin supplement to ensure that your body receives the necessary vitamin(s). If you're going to take a vitamin supplement to promote health, stay within the amount of vitamins most healthy adults need each day (RDA). The RDA is the amount of a nutrient considered to be enough to meet the needs of nearly all healthy individuals in each age and gender group. Both taking too much or getting too little of a certain vitamin can cause health problems.

Take vitamin B6 (pyridoxine) as an example. If you have too little vitamin B6 in your body, nerve problems may result. Interestingly, if you get too much vitamin B6, that can also cause a problem with your nerves. You need just the right amount of B6 for your body to function properly. Fortunately, vitamin B6 is found in a wide variety of foods, such as cereal grains, carrots, peas, spinach, milk, cheese, eggs, fish and flour, so it's uncommon to have a vitamin B6 deficiency that would require a supplement.

Although taking lots of vitamins might seem like a good idea, be careful. Avoid taking too much of any individual vitamin, especially fat-soluble vitamins (vitamins A, D, E and K). Too much vitamin A, for example, has been shown to be related to birth defects and hip fractures. Even too much vitamin D, which is good for bone health, can cause problems such as excess calcium in the blood (hypercalcemia), which can lead to nausea, vomiting, poor appetite and constipation, among other symptoms. Taking megadoses of vitamins can be especially risky, as they can significantly increase the likelihood of developing health problems due to excess vitamin intake.

If you're going to take a vitamin supplement, a multivitamin is probably the best option. With most multivitamins, you will usually get close to the RDA of each individual vitamin. A multivitamin gives you a wide variety of vitamins that are approximately equivalent to your daily needs.

You may also want to consider supplements of vitamin D and calcium. Calcium is a mineral, rather than a vitamin. Vitamin D and calcium can be good for bone health. Vitamin D may have other potential health benefits, such as decreased risk of certain cancers, although researchers don't have good long-term data to prove many of them.

Finally, fish oil is a supplement that appears to be beneficial for people who have high triglyceride levels and those with heart disease. For others, it hasn't been conclusively proven that fish oil is helpful. But at this time, fish oil appears to have possible benefits with very little risk. If you like to eat fish, two servings per week may have larger health benefits than supplements.

Before you take any supplements, talk to your doctor. There may be ways to modify your diet to get the vitamins you need without taking a vitamin supplement. If a supplement is necessary to ensure good health, follow the RDA.

— Donald Hensrud, M.D., Preventive Medicine, Mayo Clinic, Rochester, Minn.