Confusion About Vitamin D and Calcium
Every year, Susan Bukata, MD, goes to the annual meeting of the American Society of Bone and Mineral Research. She gives presentations and attends them, scooping up the latest data and hobnobbing with some of the world’s foremost authorities on calcium and vitamin D. But somehow, all the new information makes these nutrients more mysterious.
So it’s no surprise that orthopedic surgeons in the trenches often wonder whether to recommend supplements to their patients.”Every year, I leave more confused than when I got there,” says Dr Bukata, who is vice chair of orthopedics at the University of California, Los Angeles Medical Center, Santa Monica, and a board member of the National Osteoporosis Foundation.
The matter is not just academic. Patients who get too little calcium and vitamin D, can break bones and not heal well from surgery. And those who get too much can suffer a range of effects, from constipation to heart disease. But what is the right amount?
For the time being, Dr Bukata and most other leading authorities in the United States recommend that doctors stick, more or less, to the 2010 Institute of Medicine (IOM) recommendations. Although amounts vary by sex and age, the recommended dietary intake for most people is about 1000 mg/day of calcium and 600 IU/day of vitamin D.
Dissent Among Experts
In the 6 years since those recommendations were issued, researcher groups have challenged the foundation of this advice, including the US Preventive Services Task Force (USPSTF), which concluded in 2013 that there was insufficient evidence for it. The USPSTF is currently reviewing the data and plans to release an update in 2018.
There is plenty to review. In the 1970s, researchers began to measure how much calcium people were excreting and how much they were taking in. If excretion was greater than intake, they theorized, bones would get weaker and become more susceptible to fracture.
That theory gained traction in 1992, when a large randomized trial showed that elderly women taking calcium and vitamin D supplements were 43% less likely to break their hips than those in a matched control group taking a placebo. But the women in the study cohort lived in institutions and had low serum vitamin D at baseline.
Since then, numerous randomized controlled trials have revealed ambiguous results. “Most people don’t need to worry about their calcium at all,” Mark Bolland, MBChB, PhD, associate professor of medicine at the University of Auckland in New Zealand, told Medscape Medical News last year after he and his colleagues published two meta-analyses on the mineral.
Dr Bolland’s team combined data from 26 studies, and calculated that calcium supplements reduced total fractures by 11% and vertebral fractures by 14%, but did not reduce hip or forearm fractures. These researchers concluded that, for most people, the risks related to calcium supplementation could outweigh the benefits.
These risks include cardiovascular events, kidney stones, and hospital admission for acute gastrointestinal symptoms.
Significant Reduction in Fracture Risk
But the naysayers did not have the last word. Researchers from seven academic medical centers in the United States—using more restrictive criteria than Dr Bolland’s team—melded data from eight studies, and found that the combination of calcium and vitamin D supplementation cut the risk for total fractures by 15% and the risk for hip fractures by 30%. They recommended supplementation with the two nutrients.
Meanwhile, a meta-analysis focusing on adverse effects demonstrated that vitamin D, given alone or in combination with calcium, increased hypercalcemia and hypercalciuria, but not the risk for kidney stones.
The IOM has not announced any plans to revise its 2010 recommendations on the basis of new data. “To date, there has been no new evidence that contradicts the recommendations made in the 2010 IOM report,” says A. Catharine Ross, PhD, lead author of the report and a nutrition professor at Pennsylvania State University in University Park. “Several new studies are known to be underway, and their results are awaited with interest.”
Dr Ross still believes that the doses in the IOM recommendations can get most patients into the bottom of a U-shaped risk curve, between the high risk for fractures and high risk for adverse effects.
Dr Bukata agrees. “Calcium and vitamin D alone do not prevent fracture,” she says. “But if you don’t have enough calcium and vitamin D, you can increase your risk of fracture.”
Patient Age, Diet, and Other Variables
The need for supplements containing these nutrients depends not only on a person’s age and sex, but also on diet, sun exposure, skin pigment, and health conditions, such as obesity. Dr Bukata says she often finds herself reassuring colleagues that they don’t have to precisely calculate prescriptions; most patients do well on 2000 IU of vitamin D and 500 mg calcium per day.
Although this is a lot more vitamin D than the IOM recommends, Dr Bukata says it might be necessary to boost serum levels of the nutrient to within a normal range, citing American Endocrine Society guidelines.
Younger patients might need only 1000 IU of vitamin D, she says, and some patients can skip the calcium. “If the patient is eating a relatively normal diet, where they have some dairy, and they’re between 21 and 50 years,” she says, “they probably don’t need a calcium supplement.”
You can get 42% of your daily calcium requirement in 8 ounces of yogurt. In addition to dairy, some vegetables, including Chinese cabbage, kale, and broccoli, are rich in calcium. And many fruit juices, tofu, and cereals come fortified with the mineral.
In contrast, most patients don’t get enough vitamin D from their diets. Although it does occur naturally in fatty fish, such as salmon, tuna, and mackerel (3 ounces of salmon is enough for the day), few Americans eat fish every day. Even a cup of milk fortified with vitamin D only has 34% of the daily requirement for most people.
Skin exposed to ultraviolet radiation can synthesize vitamin D, but patients have to balance the benefits of exposure and the risk for skin cancer, and researchers have not come up with clear guidelines for this.
For this reason, Dr Bukata is less likely to recommend that her patients skip vitamin D supplements than calcium supplements. Vitamin D is essential not only for calcium absorption, but also for immune function. “I tell my patients, if you only do one thing, please take the vitamin D,” she says.
When in doubt, she points out, you can check a patient’s serum 25-hydroxy vitamin D. A healthy minimum level is somewhere between 20 and 30 ng/mL, she says, although it is considered safe at much higher levels.
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