Vitamin D and Calcium for Bone Health: Getting the Right Amount

Vitamin D (CALCIFEROL) and calcium play an important role in bone health, and for some people, taking dietary supplements containing these nutrients may lower the risk of broken bones. Yet there is also evidence that vitamin D and calcium supplements may actually increase the risk of kidney stones and potentially cause other rare but dangerous side effects. Making sense of all the different messages about vitamin D and calcium supplements can be difficult. There are, however, a few clear steps you can follow to make sure you are getting the vitamin D and calcium you need to stay healthy and avoid unnecessary risks.

What most adults need

Vitamin D and calcium work together to help maintain bone health by ensuring that the body creates and reabsorbs bone tissue at roughly the same rate, thus avoiding a net loss of bone. Although scientists are exploring a wide range of possible benefits unrelated to bone health, the results of their studies have remained mixed. The Institute of Medicine (IOM), a nonprofit that, among other things, determines the recommended daily allowances used in food nutrition labels, recently reviewed more than 1,000 studies of vitamin D and calcium and found that the only health benefit demonstrated by reliable studies was the benefit to bone health.

For most adults, the daily allowance for calcium recommended by the IOM is 1,000 milligrams (mg). For vitamin D, the recommended daily allowance for most is 600 international units (IU).

Recommendations for special populations

For certain groups, the IOM’s daily allowance recommendations are higher. Because bone reabsorption increases with age, postmenopausal women and men over 70 are at higher risk of fractures. People who exercise regularly throughout their lives tend to experience less of this bone loss later in life. It may also be possible for older adults to reduce some of this risk by consuming higher amounts of calcium and vitamin D. The IOM recommends that women increase their daily calcium intake to 1,200 mg after they turn 50. Men’s calcium needs adjust slightly later than women’s, so the IOM recommends that men wait until age 70 to increase their daily calcium intake to 1,200 mg. The need for vitamin D is the same for men and women: all adults should increase their vitamin D intake when they turn 70 from the 600 IU to 800 IU per day.

Some groups at high risk for vitamin D and calcium deficiency could benefit from changes in diet. Adolescent girls, postmenopausal women and adults older than 70 are at increased risk of calcium deficiency. People who get little sun exposure (for example, because they live in a nursing home) may be at risk of vitamin D deficiency. However, some reports of prevalence of vitamin D deficiency may be exaggerated.

The role of diet and exercise

One of the best ways to ensure adequate intake of nutrients while avoiding side effects is to maintain a balanced diet. Meals rich in low-fat dairy and dark green vegetables promote calcium intake. Fatty fish like salmon or tuna deliver vitamin D.

An easy way to increase calcium and vitamin D intake in your diet is to drink low-fat milk or eat cheese or breakfast cereal fortified with vitamin D. Studies have shown that consuming vitamin D-fortified milk or cheese can have a favorable impact on bone health and may help prevent osteoporosis or reduce the risk of broken bones.

The body also uses sunlight to create its own vitamin D, and spending limited time in the sun is another healthy way to obtain this nutrient. Remember to wear sunscreen and limit your exposure to avoid tanning or burning, which increases the risk of skin cancer.

Generally, it is not necessary to increase your daily dietary intake above the recommended amount through supplements or special diets. This is because the recommended daily allowance for vitamin D is designed to be high enough to satisfy the needs of people who get only minimal sun exposure (including people living at high altitudes during winter).

When more is not better

In addition to recommending optimal daily intake of vitamin D and calcium, the IOM has analyzed the best available evidence on risks to set maximum daily intake limits for the nutrients. These limits are not goals but instead represent levels above which harmful side effects are well-documented. For calcium, the daily limit, not to be exceeded, is 2,000 mg for adults over 50 years old. For younger adults, the limit is 2,500 mg, with different recommendations for children and adolescents. For vitamin D, the daily limit is 4,000 IU for all adults and most adolescents, with lower limits for children.

It may be particularly easy to exceed the upper-level intake limits with calcium, because the daily limit is relatively low and calcium is available in many foods. For example, a 65-year-old woman who takes a 1,000-mg calcium supplement, drinks two cups of milk (830 mg calcium) and eats a small, four-ounce container of yogurt (207 mg calcium) is getting 2,037 mg of calcium — over her daily limit.

Dietary supplements may be an easy way to get vitamin D and calcium, but they also make it too easy to consume too much and develop harmful side effects. Both vitamin D and calcium can cause buildup of calcium in the blood, which in turn can result in kidney stones or other symptoms such as fatigue, muscle and joint aches, nausea, heart rhythm disturbances, and, in rare cases, kidney failure. In addition to calcium buildup, vitamin D, at high doses can be toxic and even fatal.

Studies have shown increased risk of certain side effects even with relatively low-dose supplements. In one study, 1 in every 273 women who took low-dose vitamin D (400 IU/day) and calcium (1,000 mg/day) supplements over a seven-year period developed kidney stones as a result.

Who can benefit from supplements?

Vitamin D and calcium supplements are probably not necessary for most healthy adults, and easy-to-accomplish improvements in diet will probably be enough to address any insufficiency. However, supplements may help for certain limited groups of people. Supplements have been shown to reduce the risk of broken bones for adults older than 65 who live in nursing homes, hospitals or other institutions. This may be because older people living in institutions do not get adequate nutrition or exposure to sunlight. Supplements may also benefit those who have a health condition or who take drugs that affect calcium or vitamin D absorption.

For other groups, it is still not possible to say with certainty whether vitamin D and calcium supplements help or hurt. In June 2012, the U.S. Preventive Services Task Force, a panel of independent experts focused on evidence-based disease prevention, issued a draft statement concluding that for most healthy women and men, including adults over age 65 who do not live in institutions such as nursing homes, there is not enough evidence to recommend for or against taking moderate-to-high daily doses of vitamin D (more than 400 IU) with calcium (1,000 mg) to prevent bone fractures (and low-dose supplements [less than 400 IU] were even worse in terms of benefits).

Scientists have explored whether vitamin D and calcium supplements can help people with osteoporosis, or those at high risk of falls, but there is still no conclusive evidence that people from these groups need to take supplements if their diet is adequate and they have normal levels of vitamin D in their blood.

What You Can Do

If you are a healthy adult under age 65 who eats a balanced diet, you are probably not at risk of vitamin D or calcium deficiency and do not need to consider supplements. If you fall into one of the groups at high risk for deficiency, a good way to increase your intake of these vitamins safely is to add a serving or two of vitamin D-fortified milk, cheese or yogurt to your diet each day. Consuming calcium and vitamin D in the amounts found in food is unlikely to lead to harmful effects.

If you live in an institution, you should approach your doctor about starting vitamin D and calcium supplements. You may also consider talking to your doctor about starting supplements if you have osteoporosis, a history of falls or a health condition that puts you at greater risk for vitamin D deficiency, but remember that the evidence is not clear about whether supplements will generally help or hurt people with these conditions.

Before starting supplements, your doctors should evaluate you to see if you are at risk of developing kidney stones or other side effects. If you have decreased renal (kidney) function or take a thiazide-based diuretic, this can affect your body’s ability to eliminate excess calcium.

Ask your doctor about testing the levels of calcium and vitamin D in your body to see if you are deficient. (And double check your lab results: some labs use a higher cutoff than the 20 nanograms per milliliter of calcium, the level needed for good bone health according to the IOM). Once you start taking supplements, your doctor should run a second set of tests to make sure the supplements are being absorbed properly and may wish to run more tests as you continue to take supplements.

If you do take supplements, you should aim to keep your daily intake from food and supplements close to the recommended levels.

In some cases, your doctor may recommend that you take a very high dose of vitamin D, which your body can store and use slowly over weeks or even months. This is acceptable as long as the dose averages out over time to close to the daily recommended intake of 600 or 800 IU. However, you should avoid taking this approach unless your doctor recommends it after careful evaluation and is prepared to monitor your body’s response to treatment. Vitamin D can be toxic, and even fatal, when high doses are taken incorrectly.