High calcium intake doesn't prevent broken bones

BMJ Group News

Getting more than the recommended daily amount of calcium doesn't stop women getting osteoporosis, researchers have found. Low calcium intake can lead to weak bones, but the risk goes away for women who get around 700 milligrams of calcium a day, and there’s no benefit to having more.

What do we know already?

Osteoporosis causes around 200,000 broken bones every year in the UK. Older women are most at risk, with more than 1 in 3 women suffering at least one broken bone because of osteoporosis during their lifetime.

Calcium plays an important part in keeping bones healthy, along with vitamin D, which helps the body absorb calcium from food. It's not clear exactly how much calcium people need though, and the recommend intake varies from country to country. The NHS recommends that adults get 700 milligrams a day, but in the United States and Australia the recommended intake for older women is almost double this.

Calcium has become even more controversial recently, with several studies suggesting that taking extra calcium as supplements could increase a woman's risk of a heart attack.

Now, a new study has looked at more than 60,000 women in Sweden, with an average age of 53, to look at whether the amount of calcium they got affected their risk of developing osteoporosis or breaking a bone.

What does the new study say?

Unsurprisingly, women with the lowest intake of calcium had a higher risk of getting fractures or developing osteoporosis. But the risk disappeared once women reached about 700 milligrams of calcium a day. Higher amounts of calcium didn't cut the risk any further.

The researchers split the women into five groups, based on the amount of calcium they were getting. The women with the lowest calcium intake had a 17 in 1,000 risk of a broken bone over a year. In the middle group, this fell to 14 in 1,000. The two groups with the highest calcium intake also had a risk of around 14 in 1,000 per year.

The pattern was the same when the researchers looked at calcium supplements the women were taking, as well as calcium from food.

During the 19-year study, 1 in 4 women got a broken bone. Some of the women were offered bone x-rays to check for osteoporosis, and around 1 in 5 women were diagnosed with the condition.

The study threw up one oddity: women who got the most calcium seemed more at risk of a broken hip. The researchers don't know why this happened, but one possibility is that women who knew they were at risk of weak bones deliberately upped their calcium intake.

How reliable is the research?

The study was carefully done, and took into account several factors that could have affected women's bone strength, such as whether they smoked, how much exercise they did, and their vitamin D intake. However, it's impossible to rule out some other factor that could have influenced whether they got osteoporosis.

The researchers used questionnaires to find out how much calcium women were getting from food. These aren't always reliable, as it's easy to misremember how often you eat particular foods.