Vitamin D - Protecting Your Bones: Osteoporosis
Content provided by the Faculty of the Harvard Medical School
Vitamin D
Vitamin D is essential to bone health. It plays a vital role in calcium absorption by allowing calcium to travel out of the intestines and into the bloodstream. A 2003 study found that vitamin D supplementation increased calcium absorption by 65%.
Other studies uncovered a relationship between low levels of vitamin D and low bone density, and there is some evidence that older women who don't get enough of this vitamin are at greater risk for hip fracture. A 2002 meta-analysis published in Endocrine Reviews also found that vitamin D supplements may reduce the risk for spine fractures by 37%. Why the decrease in fractures? The Surgeon General's report on osteoporosis speculated that vitamin D may actually reduce a person's risk of falling by activating receptors on muscles that play a role in increasing muscle strength and stability.
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 While your body produces vitamin D from sunlight, most people need a supplement to get the recommended amount of this vitamin. |
Current vitamin D recommendations are 200 IU for people ages 1–50, 400 IU for people ages 51–70, and 600 IU for people ages 71 and older. However, there is some evidence that we need more vitamin D than the currently recommended levels. With this in mind, some experts suggest getting as much as 800–1,000 IU of vitamin D per day.
If you don't get an adequate amount of vitamin D, your body won't be able to absorb enough calcium from the foods you eat and instead will rely on the calcium in your bones. That's the case for many adults. One survey published in the June 2004 Journal of the American Dietetic Association found that two in three Americans between ages 51 and 70 fall short of the current target for vitamin D. The situation is even worse for older people, with 9 in 10 not getting enough of the vitamin.
Vitamin D is made in the skin after exposure to sunlight. Some people make all the vitamin D they need by going outside for a few minutes a day without sunscreen. You should keep your exposure time short — just 10 to 15 minutes a day — to protect against skin cancer. However, you may find that sunlight alone won't generate adequate amounts of vitamin D. For example, if you live above 40 degrees latitude (the latitude of Denver, Indianapolis, and Philadelphia), the winter sunlight isn't strong enough to enable you to produce significant amounts of vitamin D. Sunscreen, glass, and clothing also interfere with this process, diminishing your ability to produce the vitamin. And as you age, your skin can't produce vitamin D as readily, and your intestines have more difficulty absorbing this vitamin.
Limit caffeine, protein, and vitamin AIn high amounts, some substances — such as caffeine, protein, and vitamin A — can harm your bones, so it's wise to keep a watchful eye on just how much of these you're getting. Some preliminary research suggests that drinking four or more cups of coffee a day can put you at greater risk of breaking a bone. It seems that high levels of caffeine may increase calcium excretion in the kidneys. More study is needed, but in the meantime you may want to forgo that fourth cup. High levels of protein, particularly protein from animal sources, may also cause calcium to leach from your bones. Experts haven't pinpointed a cutoff amount, but they suggest that you keep an eye on the amount of animal protein you get. Several studies have found a link between high vitamin A intake and fractures. A 2002 study in the Journal of the American Medical Association found that postmenopausal women who got more than 3,000 mcg of vitamin A were more likely to break a hip. And a 2003 study in the New England Journal of Medicine found that men with the highest amounts of vitamin A in their blood were also at greatest risk of breaking a bone. Currently, the recommended daily amount of vitamin A is 700 mcg (about 2,300 IU) for women and 900 mcg (about 3,000 IU) for men. You can get vitamin A through the nutrient beta carotene or as preformed vitamin A. Beta carotene has not been linked to hip fractures. Thus, it's safer to get your vitamin A in this form. If you take a multivitamin that contains vitamin A, check to make sure that a significant part of its vitamin A comes from beta carotene. Also, avoid taking high-potency vitamin A supplements.
 Keeping your coffee intake to three cups or less a day may benefit your bones. |
You can try to make up for the shortage with your diet, but only a few foods — such as eggs, saltwater fish, and liver — contain vitamin D. In the United States, milk is fortified with this vitamin; an 8-ounce glass should have about 100 IU. Ultimately, taking one daily multivitamin may be the easiest way to ensure that you get enough vitamin D. Most multivitamins contain 400 IU.
Because too much of this vitamin can be dangerous, keep your daily intake below 2,000 IU. In general, you'll get far less than that from food, sunlight, and a multivitamin, but if you're taking several different vitamin pills, it's important to review your daily dose.
Get your vitamin KYou know that calcium and vitamin D are good for your bones, but did you know that vitamin K may also keep them strong? That's what research indicates. Vitamin K helps produce osteocalcin, a protein that is instrumental in bone formation. It also blocks substances that break down bone and helps regulate calcium excretion from the body in urine. A 2002 study published in Maturitas concluded that therapy with vitamins D and K might increase bone mass in postmenopausal women. Researchers have also found that getting ample vitamin K protects against hip fracture. According to the Nurses' Health Study, women who got at least 100 micrograms (mcg) of vitamin K a day were 30% less likely to break a hip than the women who got less than that amount. Similarly, the Framingham Heart Study found that the participants who got the most vitamin K were less likely to break a hip than those who got the least amount. How much vitamin K should you get? Current recommendations are 120 mcg per day for men and 90 mcg for women. Most diets supply more than this. Good sources of vitamin K are spinach, broccoli, brussels sprouts, collard greens, and other green leafy vegetables. As with anything, moderation is important; taking excessive doses of vitamins can have negative effects. If you take anticoagulants like warfarin (Coumadin), it's particularly important to keep your vitamin K intake consistent from day to day, since this vitamin influences blood clotting. If you take an anticoagulant, it's wise to talk to your doctor before taking vitamin K. |
| Last updated: | January 23, 2007 |
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Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.
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