Healthy Eating: Beating Bone Loss
Your diet: Osteoporosis
Calcium is the one nutrient that comes to mind when most people think of preventing osteoporosis, a loss of bone mass that often increases with age and can lead to fractures (see Figure 3). Calcium is an important nutrient for building bone and for slowing the pace of bone loss that comes with age. But it’s not the single magic bullet for preventing osteoporosis, and some scientists suggest that too much calcium or dairy products may be unhealthy. Keep in mind that in addition to calcium, there are other nutrients and foods that help keep your bones strong — most importantly vitamin D, but also vitamin K and possibly fish.
Figure 3: Osteoporotic bone
As the illustration above reveals, osteoporotic bone is more porous and less dense than healthy bone. The result is bone that is fragile and more vulnerable to breaks. But strength training can slow bone loss and even help build bone.
How much calcium? The DRI for calcium is 1,000 mg a day for adults up through age 50 and 1,200 mg a day for people ages 51 and older, when bone loss accelerates. With age, the intestines absorb less calcium from the diet, and the kidneys seem to be less efficient at conserving calcium. As a result, your body uses more of the calcium stored in your bones for a variety of important metabolic functions.
Scientific studies have yielded different results regarding how much calcium you really need for preventing age-related bone loss. For example, a report in The American Journal of Clinical Nutrition in 2003 found that calcium intake during youth pays dividends many decades later. In this study of 3,215 women, those women over age 50 who, as children, drank very little milk (less than one serving a week) were twice as likely to fracture a hip as women who had consumed more than one serving a day. But calcium intake during adulthood may not have the same benefit. Seven studies done in the United States and Europe that have followed thousands of people for many years have found no correlation between a high intake of calcium in adulthood and fewer bone fractures. For example, in the Nurses’ Health Study and the Health Professionals Follow-up Study, people who drank two or more glasses of milk a day were no less likely to break a hip or forearm than people who drank one glass or less a week.
Because preliminary findings suggest that high calcium intake may increase the risk of prostate cancer (see “Preventing prostate cancer”), men should avoid taking calcium supplements or taking too many calcium-rich antacids.
Vitamin D. In building bone, calcium has an indispensable assistant: vitamin D. This vitamin helps the body absorb calcium, and some researchers think that increasing vitamin D can help prevent osteoporosis. Milk sold in the United States is fortified with vitamin D. Vitamin D is also prevalent in fortified breakfast cereals, eggs, and vitamin supplements. Other dairy products made from milk, such as cheese, yogurt, and ice cream, aren’t typically fortified with vitamin D and contain only small amounts. However, some brands of yogurt are fortified with it, as well as some juices. If possible, a small amount of sun exposure can help your body manufacture its own vitamin D — about five to 30 minutes of sunlight between 10 a.m. and 3 p.m. twice a week to your face, arms, legs, or back without sunscreen will enable you to make enough of the vitamin. People with fair skin that burns easily should protect themselves from skin cancer by limiting sun exposure to 10 minutes or less. Food and sun exposure should suffice, but if not, some experts advise getting 1,000 IU of vitamin D daily from a supplement.
Vitamin K. The Nurses’ Health Study found that women who got more than 109 mcg of vitamin K a day were 30% less likely to break a hip than women who got less. To get enough vitamin K, eat one or more servings daily of dark green lettuce, broccoli, spinach, Brussels sprouts, or kale. Vitamin K helps regulate calcium and build bone.
Vitamin A. Eating too much vitamin A can increase your risk of osteoporosis. Scientists have known for years that megadoses of vitamin A can deplete bone by interfering with the ability of vitamin D to maintain sufficient calcium levels. Then in 2002, Harvard researchers involved with the Nurses’ Health Study reported that vitamin A may promote bone loss even at levels considered safe. In the study, postmenopausal women who ingested 3,000 mcg or more per day of vitamin A from food, supplements, or both over an 18-year period were more than twice as likely to fracture a hip as women who had less than 1,500 mcg daily.
The DRI for vitamin A is 700 mcg for women, with levels up to 3,000 mcg considered safe. The Nurses’ Health Study suggests that postmenopausal women are best off with a vitamin A intake in the lower half of this range. To make sure your intake is at the right level, read the labels of the foods you often eat to see how much vitamin A they contain, paying special attention to fortified breakfast cereals. If you take a multivitamin, see how much vitamin A it has. If your multivitamin contains more than the DRI, consider switching to a brand with a lower amount. However, beta carotene, often used in multivitamins as a source of vitamin A, doesn’t pose this risk.