Time-release vitamins -- supplements designed to slowly release vitamins over an extended period of time -- appear to offer more health benefits than regular vitamins. However, health authorities, including the Harvard School of Public Health, say that time-release vitamins are not particularly useful. In some cases, time-release vitamins may be prescribed to treat a health condition, but taking over-the-counter time-release vitamins can be dangerous.
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The theory behind time-release vitamins is that they deliver a steady amount of vitamins into your bloodstream over the course of the day. However, unlike time-release medications, time-release vitamins are are no more effective than regular vitamins, and they usually cost more, according to the Harvard School of Public Health. According to Columbia University Health Services, most people do not need the constant influx of vitamins advertised by time-release vitamins, and time-release vitamins may also be dangerous as well as ineffective. Supplements containing time-release niacin, for example, cause fewer side effects than regular niacin supplements but are associated with liver damage.
There is not s significant body of research on time-release vitamins, but the existing research indicates that time-release vitamins sold as nutritional supplements are perhaps even less effective than regular vitamins and may be dangerous. According to the Linus Pauling Institute at Oregon State University, one study found that a time-release vitamin C capsule was 50 percent less bioavailable than other formulations of vitamin C, and another study found no difference in the body's absorption of time-release vitamin C versus regular vitamin C. Regarding time-release niacin, a review published in "Expert Opinion on Pharmacotherapy" in 2004 concluded that while time-release niacin sold as a nutritional supplement is associated with liver toxicity, a prescription-only, time-release formulation of niacin does not carry the same health risk.
What to Look for in a Vitamin
According to the Harvard School of Public Health, people looking to take a vitamin for general health should look for a multivitamin that supplies 100 percent of the dietary reference intakes for most vitamins, avoiding extended release and "mega" vitamins that supply 200 percent of the DRI or more. High-doses vitamins, including many time-release preparations, may cause liver problems and other toxic effects, particularly with fat-soluble vitamins such as vitamin A and E. The exception to the "100 percent DRI" rule, according to HSPH, is vitamin D, as many people need more than the DRI. If you have dark skin or little exposure to direct sunlight, have your doctor check your vitamin D status.
Unless your doctor recommends you take vitamins due to a medical condition or dietary insufficiency, you probably don't need to take a multivitamin. As long as you are generally healthy and eat a varied diet that includes fruits, vegetables, whole grains, legumes, low-fat dairy, lean meats and fish, you probably receive the nutrients you need from food. In general, whole foods are preferable to vitamins as they also contain micronutrients and fiber. While taking a regular multivitamin that contains 100 percent of the DRI is likely safe for most people, high-dose, time-release vitamins should only be taken under the supervision of a doctor.