One of the most contentious questions in nutrition science over the past decade has been whether older adults should be taking supplemental vitamin D and calcium.

As the world's population ages and broken bones and fractures become even more of a public health concern, with huge social and economic consequences, researchers have been trying to make sense of conflicting studies on the association between supplements and fracture risk.

A study published in the Journal of the American Medical Association on Tuesday took a fresh look at this issue by analysing 33 randomised clinical trials involving a total of more than 50,000 adults over the age of 50.

Each of these previous research papers involved comparing calcium, vitamin D, or both, with a placebo or no treatment.

The analysis, conducted by Jia-Guo Zhao of Tianjin Hospital in China, was focussed on older adults who live in the general community and did not include those in nursing homes, hospitals, and other facilities.

The conclusion was clear: vitamin D and calcium supplements do not seem to be warranted to prevent bone breaks or hip fractures in those adults. Such supplements had no clear benefit regardless of dose, the gender of the patient, history of fractures, or the amount of calcium in the diet.

The US Preventive Services Task Force, an influential federal advisory body, has raised questions about these supplements since 2013, when it issued recommendations saying evidence to support the benefit of the supplements in older adults without osteoporosis or vitamin D deficiency was "insufficient".

Marion Nestle, a professor emerita of food sciences and nutrition at New York University, wrote in an opinion piece at that time that the UPSTF's statement should caution clinicians "to think carefully before advising calcium and vitamin D supplementation for healthy individuals".

She said this week bone health involves many different aspects of eating and activity.

"Bone preservation throughout life requires eating healthfully, engaging in weight-bearing activity, avoiding excessive alcohol, and not smoking - good advice for everyone," Nestle said.

Vitamin D is not a vitamin but a hormone that is produced in reaction to sunlight and seems to have many different roles in the body related to bones, cancer, heart disease, diabetes, immune function, and reproductive health.

Daniel Fabricant, president of the Natural Products Association, which represents manufacturers and retailers of dietary supplements, said the study draws its conclusions with "too broad of a brush".

He said it focusses on the healthiest segment of the population by looking at people who are able to live at home.

"There is a lot missing," Fabricant said. "People with prior breaks or family incidence of osteoporosis may still need vitamin D."

Calcium and vitamin D have been known to be important to bone maintenance for a long time, and the best way to get the daily recommended doses are the natural way.

For calcium, that means eating dairy products like milk, cheese, yogurt or calcium-rich leafy greens. For vitamin D, that means getting some sun exposure. Only a few foods contain vitamin D, and they include fatty fish like salmon.

The issue is many Americans don't get enough calcium or vitamin D - which is why the debate over supplements has become so important.

In 2010, the Institute of Medicine (IOM) released recommendations tripling the daily intake of vitamin D for most people to 600 IU per day and raising the calcium intake to 1,000 milligrams.

While that report has few explicit mentions of supplements, the use of supplements seems assumed, and it includes a lot of discussion about the importance of setting and following upper limits for intake of vitamin D and calcium.

"As North Americans take more supplements and eat more of foods that have been fortified with vitamin D and calcium, it becomes more likely that people consume high amounts of these nutrients," the group wrote, warning of the possibility of kidney and tissue damage from overconsumption.

Fabricant also said the new study contained limited information on the dosages involved. "Maybe the average dose was on the lower end of dose response curve," he said.

"While it's a nice exercise of mathematics, it doesn't get at the actual issue, which is what are optimal levels for people who need the supplements?"

The new study did not look at the benefits or risks of vitamin D supplements on other conditions, but previous studies have suggested they can lower risks for diabetes and certain cancers.

However, an April 2017 study in JAMA Cardiology found high monthly doses of vitamin D supplements did not seem to do much to help with cardiovascular disease.

One other limitation of the study is some of the trials included in the analysis did not test baseline vitamin D blood concentration for all participants.

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This article was originally published by The Washington Post.