How much vitamin D do you need? Despite widespread assertions in the popular and scientific press that many Americans have a vitamin D deficiency, the term "deficiency" isn't strictly accurate. The official definition of a vitamin deficiency means that specific health problems stem solely from the lack of (or inability to use) a specific nutrient. An actual vitamin D deficiency results in bone disease, such as rickets, which is rare in the United States.  On the other hand, lower-than-optimal levels of specific vitamins, including vitamin D, may increase your risk of numerous health problems, even though they are not solely responsible for these problems. "Insufficiency" may be a better term for these lower levels than "vitamin D deficiency".  Get your copy of Making Sense of Vitamins and Minerals   About half of all Americans routinely take dietary supplements. The most common ones are multivitamin and multimineral supplements. Making Sense of Vitamins and Minerals: Choosing the foods and nutrients you need to stay healthy explains the evidence behind the benefits and safety profiles of various vitamins and minerals. It also includes the recommended minimum and maximum amounts you should consume, as well as good food sources of each. So far, the most clearly established benefit of vitamin D is that it helps the body absorb calcium and therefore promotes healthy bones. However, a steady drumbeat of studies beginning in the 1980s started to build a case that low blood levels of D were connected with a variety of chronic health problems, leading to claims by a number of researchers that the RDA for D was way too low. The confusion and controversy surrounding optimal vitamin D intake and blood values prompted the U.S. and Canadian governments to request that the Institute of Medicine (IOM, now called the Health and Medicine Division) review the evidence on vitamin D and calcium and update the DRIs.  The long-awaited report, Dietary Reference Intakes for Calcium and Vitamin D, was published in 2011. The IOM concluded that evidence for benefits other than improved bone health came from studies that could not be considered reliable and provided often-conflicting results.  Based on the evidence for bone benefits, however, the IOM panel increased the RDA for vitamin D to 600 IU for people up to age 70 and to 800 IU for those over 70. That's a fairly sizable boost over the previous recommendations of 200 IU per day through age 50, 400 IU for ages 51 to 70, and 600 IU for ages over 70. The IOM also raised the safe upper limit of daily intake for most age groups from 2,000 to 4,000 IU.  But ultimately, the amount of vitamin D that makes it into your bloodstream is more important than how much you're consuming. There again controversy reigns. While some people argue for much higher levels, the IOM report concluded that vitamin D blood levels above 20 ng/ml are adequate for maintaining healthy bones, and that most people in the United States have values in that range. Other organizations, including the American Association of Clinical Endocrinologists, assert that values between 30 and 50 ng/ ml have potential health benefits beyond bone health, so the issue is still not resolved. However, the IOM report cautioned that exceptionally high levels of vitamin D have not been proven to confer additional benefits and have been linked to health problems, challenging the notion that "more is better."  Most healthy adults without symptoms related to vitamin D deficiency do not need to have their blood levels measured. People who should consider vitamin D testing are those with medical conditions that affect fat absorption (including weight-loss surgery) or people who routinely take anticonvulsant medications, glucocorticoids, or other drugs that interfere with vitamin D activity. To learn more about the vitamins and minerals you need to stay healthy, read Making Sense of Vitamins and Minerals, a Special Health Report from Harvard Medical School.  Share this story:

Understanding antioxidants Some vitamins and minerals — including vitamins C and E and the minerals copper, zinc, and selenium — serve as antioxidants, in addition to other vital roles.  "Antioxidant" is a general term for any compound that can counteract unstable molecules called free radicals that damage DNA, cell membranes, and other parts of cells. Because free radicals lack a full complement of electrons, they steal electrons from other molecules and damage those molecules in the process. Antioxidants neutralize free radicals by giving up some of their own electrons. In making this sacrifice, they act as a natural "off" switch for the free radicals. This helps break a chain reaction that can affect other molecules in the cell and other cells in the body. But it is important to recognize that the term "antioxidant" reflects a chemical property rather than a specific nutritional property.  While free radicals are damaging by their very nature, they are an inescapable part of life. The body generates free radicals in response to environmental insults, such as tobacco smoke, ultraviolet rays, and air pollution, but they are also a natural byproduct of normal processes in cells. When the immune system musters to fight intruders, for example, the oxygen it uses spins off an army of free radicals that destroy viruses, bacteria, and damaged body cells in an oxidative burst. Some normal production of free radicals also occurs during exercise. This appears to be necessary in order to induce some of the beneficial effects of regular physical activity, such as sensitizing your muscle cells to insulin.  Because free radicals are so pervasive, you need an adequate supply of antioxidants to disarm them. Your body's cells naturally produce some powerful antioxidants, such as alpha lipoic acid and glutathione. The foods you eat supply other antioxidants, such as vitamins C and E. Plants are full of compounds known as phytochemicals—literally, "plant chemicals"—many of which seem to have antioxidant properties as well. For example, after vitamin C has "quenched" a free radical by donating electrons to it, a phytochemical called hesperetin (found in oranges and other citrus fruits) restores the vitamin C to its active antioxidant form. Carotenoids (such as lycopene in tomatoes and lutein in kale) and flavonoids (such as flavanols in cocoa, anthocyanins in blueberries, quercetin in apples and onions, and catechins in green tea) are also antioxidants.  News articles, advertisements, and food labels often tout antioxidant benefits such as slowing aging, fending off heart disease, improving flagging vision, and curbing cancer. And laboratory studies and many large-scale observational studies (those that query people about their eating habits and supplement use and then track their disease patterns) have noted antioxidant benefits from diets rich in them, particularly those coming from a broad range of colorful vegetables and fruits. But results from randomized controlled trials of antioxidant supplements (in which people are assigned to take specific nutrient supplements or a placebo) have not supported many of these claims. Indeed, too much of these antioxidant supplements won't help you and may even harm you. It is better to supply your antioxidants from a well-rounded diet. To learn more about the vitamins and minerals you need to stay healthy, read Making Sense of Vitamins and Minerals, a Special Health Report from Harvard Medical School. Share this story:

Featured in this issue

Making Sense of Vitamins and Minerals Featured content: • Vitamins and minerals: The basics • Understanding the federal guidelines • Making sense of scientific studies • Cast of characters: From vitamin A to zinc • Beyond vitamins: Omega-3s, phytochemicals, and probiotics • SPECIAL BONUS SECTION: Does your diet deliver the daily recommended dose? • Getting too little Click here to read more »