(NBC NEWS) -- A new study should put the final nail in the coffin for any lingering beliefs that calcium supplements are good for you.
The new study finds that people over 50 don't get stronger bones either by taking supplements or from eating calcium-rich foods such as dairy products.
The findings, reported in the British Medical Journal's online publication BMJ.com, support what U.S. health officials have been telling Americans for a few years now — taking calcium supplements is not just a waste of time, but it could be harmful. The extra calcium doesn't go to strengthen bones but instead can build up in the arteries, causing heart disease, or in the kidneys, causing kidney stones.
Dr. Ian Reid of the University of Auckland in New Zealand and colleagues did what's called a meta-analysis —they gathered all the high-quality studies they could find from around the world to see what they showed.
Most of the studies showed people over 50 get no benefit at all from taking either calcium supplements or from eating calcium in food. People were just as likely to have a fracture. A few studies showed that people who took calcium supplements might have a lower risk, but they were not very clear.
The most powerful type of study, a randomized controlled trial, showed no differences.
"Dietary calcium intake is not associated with risk of fracture, and there is no clinical trial evidence that increasing calcium intake from dietary sources prevents fractures," they wrote. "Evidence that calcium supplements prevent fractures is weak and inconsistent."
In 2012, the U.S. Preventive Services Task Force issued new recommendations saying there's not enough evidence to recommend taking calcium or vitamin D supplements, and recommending against it in some cases.
It's not welcome news, because the National Osteoporosis Foundation estimates that 54 million Americans are at risk of the bone-thinning disease. About half of all women over 50 will have a broken bone caused by osteoporosis.
Women over 50 are advised to get 1,200 mg of calcium a day and women under 50 are advised to get 1,000 mg a day. Men are advised to get 1,000 mg a day although men over 70 are supposed to get 1,200 mg. Dairy products are rich in calcium but so are leafy green vegetables, fortified milks such as soymilk and some juices and breakfast cereals.
And vitamin D helps the body absorb calcium. Sunlight helps the body produce its own vitamin D. The vitamin is added to some foods such as orange juice and dairy products and is found in some fish.
Despite this, most Westerners don't get enough calcium from food or supplements. Doctors had hoped that if people just took more supplements, they'd be better off, but the studies are not supporting this.
"The weight of evidence against such mass medication of older people is now compelling, and it is surely time to reconsider these controversial recommendations," Dr. Karl Michaelsson of Uppsala University in Sweden, who studies osteoporosis, wrote in an commentary.
And studies have shown that taking supplements can also cause harm.
"Clinical trials of calcium supplements at doses of 1,000 mg/day, however, have reported adverse effects, including cardiovascular events, kidney stones, and hospital admissions for acute gastrointestinal symptoms," Reid's team wrote.
"Consequently, older people have been encouraged to improve bone health by increasing their calcium intake through food rather than by taking supplements. This advice assumes that increasing dietary calcium intake to the recommended level of 1,200 mg a day or more prevents fractures without causing the adverse effects of calcium supplements."
But the published studies didn't show any benefit, Reid's team found. A second review, also led by Reid, found that people who ate the most calcium in their diets, mostly from dairy sources, tended to have slightly stronger bones as measured by bone mineral density, but this didn't translate into fewer broken bones.
Other studies have questioned the benefits of all sorts of supplements. Some might even fuel the growth of cancer.
Despite these findings, Americans love their supplements. A survey done in 2012 found 75 percent of Americans who take supplements would take them, even if they are proven not to benefit health. Americans spend $12 billion a year on supplements.
What can people do?
Exercise is one possibility. Weight-bearing exercise such as walking, running, playing tennis, lifting weights and dancing can strengthen bones. Swimming and bicycling does less to build strong bones, according to the NIH.
Cutting down on alcohol and stopping smoking can also help — both can weaken bones.