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Researchers found that older adults who were given vitamin D and calcium supplements were 9% less likely to die over three years than those given placebo pills. Vitamin D on its own, however, showed no effect on death rates.
The findings are based on data from eight past clinical trials -- where people were randomly assigned to take vitamin D (with or without calcium) or get inactive placebos for comparison.
Those types of studies offer the strongest kind of evidence on whether the supplements have health effects or not, said Dr. Lars Rejnmark, the lead researcher on the review.
A 9% dip in death risk over a three-year period might sound small. To put it in context, Rejnmark's team -- some of whom have connections to supplement makers that market vitamin D and calcium products -- estimates that to prevent one death, 151 older adults would have to take vitamin D and calcium for three years.
However, that effect is "at least as pronounced" as the benefits linked to cholesterol-lowering statins and blood pressure drugs, said Rejnmark, an associate professor at Aarhus University in Denmark.
"In my view, a 9% reduced mortality in the general population of elderly is of major importance," Rejnmark said.
"Except for stopping smoking," he added, "there are not many other known interventions that are capable (of) such a reduction in the risk of death."
Rejnmark and his colleagues report the findings in the Journal of Clinical Endocrinology & Metabolism.
For their study, the researchers combined the results from eight clinical trials that involved more than 70,000 older adults altogether -- mostly women.
In each trial, people were randomly assigned to take vitamin D or a placebo; some studies used a combination of vitamin D and calcium.
The doses varied, but most trials used a daily vitamin D dose of 10 to 20 micrograms. That is in the recommended range: in the U.S., health officials suggest that most adults get 15 micrograms (or 600 IU) of vitamin D per day, while people older than 70 should strive for 20 micrograms (or 800 IU).
In trials that used calcium, the dose was 1,000mg per day. In general, women older than 50, and all adults older than 70, are told to get 1,200mg of calcium each day.
Vitamin D and calcium are probably best known as bone-builders. Older women often take the supplements to ward off the bone-thinning disease osteoporosis.
Some trials have found that the supplement combination can prevent falls and bone fractures in the elderly. However, that probably does not explain the lower death risk in this study. When the researchers factored in hip and spine fractures, they did not account for the dip in death risk.
Another possibility is that supplements curbed people's risk of dying from cancer. There is some evidence that calcium and vitamin D may lower the odds of colon cancer, Rejnmark said. However, he added that the evidence is not yet "firm."
For now, Rejnmark said the findings support getting the recommended amounts of vitamin D and calcium.
That does not mean supplements carry no risks.
In particular, Rejnmark noted, some research has linked calcium supplements (not calcium-rich food) to an increased risk of heart attack in older adults -- though it is not clear if the supplement is to blame.
As for known side effects, calcium supplements may boost a person's risk of kidney stones. Very high levels of vitamin D can cause symptoms like nausea, vomiting, constipation and poor appetite.
In the U.S., the Institute of Medicine says people should get no more than 100 micrograms, or 4,000 IU, of vitamin D each day. The upper limit for calcium in older adults is 2,000mg.
People can, of course, get calcium and vitamin D through food too. Dairy foods are rich in calcium; other sources include greens like broccoli and kale, and fortified juices and breakfast cereals. Food sources of vitamin D are relatively few, but include fatty fish like salmon and tuna, plus fortified milk, juice and cereals.
From the June 18, 2012, Prepared Foods Daily News