News reports about the pros and cons of taking calcium and vitamin D and the importance of diet have left many people, including doctors, confused.
Bess Dawson-Hughes is director of the Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston and a professor of medicine at Tufts. She is a former president of the National Osteoporosis Foundation and served on the Council of the International Bone and Mineral Society and the Advisory Council of the National Institute of Arthritis and Musculoskeletal and Skin Diseases. She spoke with Nutrition Action’s Bonnie Liebman, who was recently diagnosed with osteoporosis of the hip, about the latest research on bone health.
Q: Why are people so confused about calcium?
A: Starting back in 2008, there was a lot of noise raised by three researchers who suggested that calcium causes heart attacks and doesn’t prevent fractures. That created a wave of additional analyses by other investigators.
Those claims made big news in the media. You know the game—the pendulum swings way over here to make some news and then, boom, it swings back to make some more news. We got a big dose of that.
Q: Does calcium cause heart attacks?
A: No. In 2015, some top researchers did a huge meta-analysis of clinical trials in which women got 600 mg to 1,500 mg of calcium a day, and they concluded that the evidence does not show that calcium causes heart attacks. So the fire has been put out. But that message didn’t make the news.
Q: Does calcium protect bones?
A: Calcium alone has not been demonstrated to reduce fracture rates. It does lower bone turnover rate—a measure of bone loss—by about 10 percent, however. And calcium together with vitamin D is effective in lowering fracture rates.
Q: If calcium prevents bone loss, why wouldn’t it also prevent fractures?
A: I think if you had enough people and followed them for long enough, you would probably see fewer fractures. But who’s going to do a trial looking for fractures in thousands of people with calcium up against a placebo? It’s not going to happen.
Q: Did calcium plus vitamin D prevent fractures in the Women’s Health Initiative?
A: Overall, that large trial found no lower risk of fractures among postmenopausal women who got 1,000 mg of calcium and 400 IU of vitamin D a day. But among women in the study who took at least 80 percent of their pills, there was a 29 percent lower risk of hip fractures in those who got calcium plus D.
What’s more, we know that women are unresponsive to calcium in the first five years after menopause.
A: When estrogen levels decline, the receptors in bone read that drop as, “We don’t need so much skeleton, so let’s ratchet down.”
So the drop in estrogen breaks down bone, which makes blood levels of calcium go up just a touch. And the body reads that as, “We’ve got a lot of calcium. Let’s turn off the system that brings in more.”
Q: Did calcium and vitamin D help older women in that study?
A: Yes. When the researchers included only women who were at least five or six years past menopause—that is, in their 60s or older—those taking calcium and vitamin D had a 21 percent lower risk of fractures than those who took the placebo.
Q: How does vitamin D help lower the risk of fractures?
A: One way is by promoting calcium absorption and therefore bone mass and strength. The other is that vitamin D affects muscle performance, balance, and the risk of falling. People who are insufficient or deficient in vitamin D have reduced balance, measured by sway tests.
Q: What is a sway test?
A: You put a person on a platform, and you measure how much the body is swaying. The more people sway, the poorer their balance. Two trials have found that vitamin D decreased sway in people who are deficient in D.
Q: How does vitamin D help?
A: It promotes type 2 muscle fibers. They’re the ones that help to catch you when you’re about to fall. They’re your rapid responder muscle fibers. So vitamin D is working through muscle as well as through bone.
Q: My lab report called my vitamin D level “insufficient” because it was below 30. Is that correct?
A: It depends. The labs go with the Endocrine Society guidelines, which recommend 30 nanograms per milliliter. They’re for people with osteoporosis or some other endocrine problem, so they’re reasonable for you.
But the National Academy of Medicine concluded that 20 nanograms per milliliter is sufficient for the general population of adults. So I think a lot of people are being treated excessively.
Q: What about people with osteopenia, or low bone mass?
A: They’re part of the general population. The weight of the evidence is that most people are going to be fine with blood levels in the mid-to-high 20s. And the doses of vitamin D that get you to 30 are where we start seeing more falls.
Q: That must have been a surprise.
A: Yes. Several years ago, researchers in Australia thought, “When seniors come in for a flu shot, we’ll give them a big blast of vitamin D, and that’ll take care of them for a year so they won’t have to remember to take their D pills.”
So they gave 500,000 IU as a single oral dose or a placebo once a year to 2,250 women over 70. And lo and behold, the women who got vitamin D had a 15 percent higher risk of falls than those who got the placebo.
Q: Could one huge yearly dose be worse than its daily equivalent?
A: I would expect that giving even 300,000 IU once a year—which is close to 800 IU per day—would also lead to more falls, but no one knows.
Q: Have studies also found more falls with high monthly or daily doses?
A: Yes. I was involved in a study run out of Zurich that gave people 24,000 IU or 60,000 IU of vitamin D a month. If you round them to their daily equivalents, we would be comparing 800 IU a day—which is the standard of care in Switzerland—with 2,000 IU a day. And we found more falls in the 2,000 IU group than in the 800 IU group. We were shocked.
A few years earlier, we had done a study with those doses—but given daily—in patients with acute hip fracture. And there were more falls in the 2,000 IU versus the 800 IU group. But it wasn’t statistically significant, so it might have been due to chance.
Q: Did people on higher doses also get more fractures?
A: In the Australian study that gave 500,000 IU once a year to seniors, they saw a 26 percent higher risk of fractures.
The two Zurich studies didn’t see an increase in fractures, but it takes huge numbers of older people to see enough fractures. And in those studies, we didn’t even get close.
However, the DO-HEALTH study of roughly 2,100 Europeans aged 70 or older, and the VITAL study of about 25,000 Americans aged 50 or older, are looking at fracture risk, and more. Both trials are giving people 2,000 IU a day of vitamin D or a placebo and will end by 2018.
So we should have some answers soon. And that’s good, because many people are taking doses higher than 800 IU.
Q: Should people even get their blood levels of vitamin D checked?
A: The International Osteoporosis Foundation guidelines, which I helped to write, say that most people don’t need to get their vitamin D tested. They just need to aim for 800 IU to 1,000 IU a day.
But there are categories of people who do need to be measured: people with malabsorption, people with osteoporosis, obese people, very dark-skinned people, people who have absolutely no sun exposure—for example, nursing home residents who don’t sit outside much.
Q: But not everyone else?
A: No. This business of measuring vitamin D in all healthy people—the walking well—is excessive. If people live in a northern climate and are not getting sun exposure that is effective—which would be the case between fall and spring—then they should take a supplement with 800 IU to 1,000 IU.
Q: Can you get enough from food?
A: No. There’s not much vitamin D in foods. It’s in foods that people don’t tend to eat daily, like fatty fish. And a serving of most fortified cereals provides only 40 IU, and a cup of milk has just 100 IU.
Q: Do foods that create acids in the body lead to bone loss?
A: Yes. In bone-forming cells, which are called osteoblasts, there are receptors for hydrogen ions, which come from acids. And when hydrogen circulating in blood binds to osteoblasts, it stimulates the production of osteoclasts, which break down bone.
In mouse experiments, the animals lose bone when their diet is acid-producing. But if you knock out the hydrogen receptor, the mouse no longer loses bone. So that’s the proof, at least in the mouse, that what’s going on at that receptor is triggering bone loss. It’s fascinating.
Q: Is there evidence in people?
A: In short-term studies, when researchers put healthy older people on bicarbonate or citrate pills—which supply alkali to neutralize acid—they consistently see less bone breakdown.
Q: Any longer studies?
A: Yes, two. A leading group in Switzerland saw improved bone mineral density and less bone loss in elders treated with alkali than in those treated with a placebo. And they saw improved bone strength and quality at every skeletal site.
But a previous British study used a lower dose of alkali and saw no improvement, and no one has figured out why. Maybe the dose was too low or maybe their diets didn’t produce much acid at the beginning of the study. The researchers didn’t assess acid excretion in urine at entry, so nobody knows what went on there.
Q: Which foods produce alkali and which produce acid?
A: Fruits and vegetables are the big sources of alkali in the diet. Protein-rich foods and grains like bread, rice, cereal, pasta—even whole grains—produce acid. But I would advise older people to cut back on grains rather than protein, because protein is extremely important for muscle and indirectly for bone.
Q: Important how?
A: There’s a fair amount of protein in bone. And consuming protein stimulates IGF-1, a growth factor that builds both bone and muscle.
In some observational studies, people who consume more protein have more lean mass and higher bone density than others. Wake Forest has an NIH grant to test a protein intervention on lean mass, muscle strength, muscle performance, and bone density, which is exciting.
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