Millions of people take calcium supplements to help keep their aging bones strong and reduce the risk of fractures. In recent years, some of them may have wondered if they should stop because of studies suggesting that supplemental calcium (usually with vitamin D) may not really help and that it may even be bad for the heart. We have repeatedly examined the research linking calcium to heart disease and not found it convincing (most recently in Calcium Pills: Heartening News). And the latest research confirms the benefits of the supplements for bones. Here’s what you need to know about calcium and other bone-healthy nutrients.
Calcium is vital for bone health. Bones constantly absorb and release calcium and other minerals, depending on factors such as hormones, exercise, genetics, and overall diet. After early adulthood, the rate at which calcium from bone is lost exceeds that at which it is replaced, resulting in insufficient bone remineralization and eventually weakness.
Calcium Supplements 101
Tips on how to choose and take calcium supplements.
What the experts say
In the past decade, there have been hundreds of studies and dozens of research reviews on the benefits of calcium supplementation, and they have yielded surprisingly inconsistent results, depending in part on the dose used, whether it was taken with vitamin D, and the age, health, diet, and hormonal status of the participants, along with genetic and other factors. Some studies found reduced fracture risk, while others found no benefit.
In 2010, the Institute of Medicine (IOM) issued guidelines on calcium, which relate primarily to bone health. It set the recommended dietary allowance (RDA) for women over age 50 and men over 70 at 1,200 milligrams a day from food (preferably) and supplements, and for younger adults at 1,000 milligrams.
In 2013, the U.S. Preventive Services Task Force concluded with “moderate certainty” that standard daily doses of calcium pills (1,000 milligrams or less) and low doses of vitamin D (400 IU or less) do not prevent fractures in postmenopausal women without osteoporosis. Thus it advised such women not to take the supplements. Because it said the evidence was inadequate, the Task Force did not pass judgment on higher doses of vitamin D (combined with calcium) for fracture risk, nor did it discuss younger women, men, people with osteoporosis, or those living in nursing homes. Many researchers raised objections to the guidelines, saying the Task Force has misinterpreted the research or at least put too negative a spin on it.
In any case, don’t expect calcium intake to have a big effect on bone mineral density (BMD) once you’re past early adulthood and have lost bone mass. Still, supplemental calcium and vitamin D have been shown to boost BMD modestly, especially in those with low dietary intakes. And every little bit helps when it comes to bone health.
The latest good news
Because of the uncertainty about the bone benefits of calcium and vitamin D supplements, a panel of experts from the National Osteoporosis Foundation conducted an updated meta-analysis on the subject, published in Osteoporosis International in 2016. They pooled data from eight well-designed clinical trials, two focusing on people with a history of fractures, and found that calcium plus vitamin D supplementation produced a 30 percent reduction in hip fractures and a 15 percent reduction in total fractures.
Got Calcium? 16 Good Sources
Here are some of the best dietary sources of calcium.
What to do about calcium
- Aim for 1,200 milligrams of calcium a day if you’re a woman over 50 or man over 70; 1,000 milligrams if you are younger. Some research suggests that 800 milligrams a day may be enough for many healthy people, particularly those with adequate vitamin D intake (see below) and a healthy diet.
- Get as much calcium as you can from foods. It’s better to get calcium from food than supplements because foods naturally rich in calcium supply many nutrients important for bones and general health. Dairy foods are the leading sources of calcium. Fish with bones, such as sardines and canned salmon, as well as dark leafy greens and most tofu, contain good amounts. Add up your food sources (see chart above and check food labels). You may be consuming more—or less—than you think.
- For people who don’t eat enough foods that are naturally rich in calcium, supplements and calcium-fortified foods can make up for the shortfall.
- Don’t exceed about 1,000 milligrams of supplemental calcium a day. High doses, especially when taken without food, increase the risk of certain kinds of kidney stones. (In contrast, foods rich in calcium, notably dairy products, seem to protect against stones.) The IOM set the upper limit at 2,500 milligrams of calcium a day (from food and supplements) for those under 50, and 2,000 milligrams for older people. If you eat a lot of dairy and calcium-fortified foods and also take a supplement, you may get up that high. On days when you eat lots of calcium-rich foods, skip the supplement or reduce the dose. If you’re prone to stones, check with your doctor before taking calcium pills.
- If you take thyroid hormones, corticosteroids, tetracycline, or iron pills, check with your doctor or pharmacist before taking calcium supplements. Calcium can interfere with the absorption of such drugs as well as some other minerals. On the other hand, reflux drugs—H-2 blockers (such as Zantac or Pepcid) and proton pump inhibitors (such as Nexium or Prilosec)—decrease calcium absorption, so you may need a higher calcium intake. People with certain disorders, such as celiac disease, also have decreased calcium absorption and may need supplements.
Vitamin D: calcium’s partner
Vitamin D promotes the absorption of calcium in the gut and helps maintain adequate calcium blood levels, thus enabling mineralization of bones. It is also needed for bone growth and remodeling. If you don’t get enough D, calcium provides much less benefit.
Vitamin D is also important because it helps reduce the risk of falls, which can result in fractures. Adequate vitamin D intake helps reduce age-related muscle loss and improves muscle function, especially in the lower legs.
For most people, foods supply only a small proportion of the vitamin D they need. Few foods naturally supply significant amounts. Oily fish and some types of mushrooms contain the most; egg yolks and liver have small amounts. The main source in the U.S. diet is fortified cow’s milk. Some soy milk, yogurt, orange juice, margarine, and breakfast cereals are also fortified.
The RDA for vitamin D is 600 IU a day for people up to age 70, and 800 IU for those over 70. We recommend 800 to 1,000 IU a day, unless you know your blood level is adequate. That usually requires a supplement. Some expert groups, such as the International Osteoporosis Foundation and the Endocrine Society, advise 1,000 to 2,000 IU daily, or even more for people who have low blood levels of D (below 20 ng/dL), especially those who have osteoporosis.
Though the skin makes the vitamin in response to sun, you shouldn’t rely on this, since D production can vary widely, depending on many factors. Notably, the skin’s ability to manufacture vitamin D declines with age, and the liver and kidneys become less efficient in converting vitamin D to its active form.
More bone-healthy nutrients
Bones need a great many other nutrients besides calcium and vitamin D to stay strong.
Vitamin K. This is needed for bones to synthesize proteins involved in calcium utilization. Many studies have found that people who consume the most vitamin K from food have higher bone mineral density and reduced risk of osteoporosis. Research on supplements has been less consistent. Still, a review in Nutrition Research found that high doses of K (at least 200 micrograms) improve bone quality and reduce fracture risk in older women. While it’s too early to recommend supplements, it’s a good idea to get more vitamin K from food—notably from broccoli, spinach, kale, and other leafy green vegetables. Vitamin K interferes with the anticoagulant warfarin (Coumadin), so if you take this drug, talk to your doctor about how much K is safe to consume.
Magnesium. Working with calcium and vitamin D, magnesium helps form and maintain bones. Many Americans fall short of the RDA for magnesium (320 milligrams a day for women, 420 for men) because of a poor diet. People with adequate magnesium intakes tend to have greater bone density, and low magnesium levels in the blood are associated with increased fracture risk. It’s not known if supplements can make a difference. While a magnesium deficiency can impair the body’s use of calcium and vitamin D, doubling or tripling the recommended magnesium intake won’t necessarily increase calcium absorption.
Adequate protein. This may protect bones primarily by reducing age-related muscle loss and thus reducing falls, a major cause of fractures. But can consuming too much protein cause calcium loss from bones? Over the years there has been much debate about this, and research has yielded inconsistent results. However, a systematic review and meta-analysis from the National Osteoporosis Foundation, in the American Journal of Clinical Nutrition in 2017, found that higher intakes of protein do not have adverse effects on bone health and may even help protect the spine. In 2018, a consensus paper endorsed by the International Osteoporosis Foundation concluded that "There is no evidence that diet-derived acid load is deleterious for bone health. Thus, insufficient dietary protein intakes may be a more severe problem than protein excess in the elderly."
Other key nutrients for bone health. These include phosphorus, potassium, fluoride, iron, zinc, copper, silicon, manganese, boron, and vitamins B12 and C. You need some vitamin A for healthy bones, but too much (more than about 10,000 IU a day from food and supplements) can cause bone loss. Substances in soy (isoflavones), fish (omega-3 fats), tea (flavonoids), olive oil (polyphenols and monounsaturated fat) and dried plums (better known as prunes, rich in antioxidants) have been linked to bone health, but research has not always been consistent. A high sodium intake causes calcium to be leached from bones.
What about strontium? This is another bone-friendly element. One form, strontrium ranelate, is approved as an osteoporosis drug in some European countries (but not in the U.S.) despite concerns that it may increase the risk of cardiovascular problems. In the U.S., other forms are sold as dietary supplements, but they have been less studied.
You can get all the nutrients discussed here in a diet rich in vegetables (especially dark leafy greens), fruits, and whole grains, plus dairy products, fish, and fortified cereals. Such a diet tends to be anti-inflammatory, which is also good for bones. This was seen in a 2017 study in the Journal of Bone and Mineral Research, which included more than 160,000 postmenopausal women who had no history of hip fractures. Their diets were scored on the Dietary Inflammatory Index, a measure of inflammatory potential based on 32 food components. Bone density was also assessed over the course of the study. After six years of follow-up, women who had the least inflammatory diets were found to have lost less bone density in the hip than those with higher inflammatory scores.
Also see Osteopenia: What to Do About Bone Loss.
(Originally published July 2017; updated September 2018)
Published September 17, 2018